S. Mrenna

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

The PYTHIA program is a standard tool for the generation of high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multihadronic final state. It contains a library of hard processes and models for initial- and final-state parton showers, multiple parton-parton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and interfaces to external programs. While previous versions were written in Fortran, PYTHIA 8 represents a complete rewrite in C++. The current release is the first main one after this transition, and does not yet in every respect replace the old code. It does contain some new physics aspects, on the other hand, that should make it an attractive option especially for LHC physics studies.

The Pythia program is a standard tool for the generation of events in high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multiparticle final state. It contains a library of hard processes, models for initial- and final-state parton showers, matching and merging methods between hard processes and parton showers, multiparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and several interfaces to external programs. Pythia 8.2 is the second main release after the complete rewrite from Fortran to C++, and now has reached such a maturity that it offers a complete replacement for most applications, notably for LHC physics studies. The many new features should allow an improved description of data. Program title: Pythia 8.2 Catalogue identifier: ACTU_v4_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ACTU_v4_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence, version 2 No. of lines in distributed program, including test data, etc.: 478360 No. of bytes in distributed program, including test data, etc.: 14131810 Distribution format: tar.gz Programming language: C++. Computer: Commodity PCs, Macs. Operating system: Linux, OS X; should also work on other systems. RAM: ∼10 megabytes Classification: 11.2. Does the new version supersede the previous version?: Yes Catalogue identifier of previous version: ACTU_v3_0 Journal reference of previous version: Comput. Phys. Comm. 178 (2008) 852 Nature of problem: High-energy collisions between elementary particles normally give rise to complex final states, with large multiplicities of hadrons, leptons, photons and neutrinos. The relation between these final states and the underlying physics description is not a simple one, for two main reasons. Firstly, we do not even in principle have a complete understanding of the physics. Secondly, any analytical approach is made intractable by the large multiplicities. Solution method: Complete events are generated by Monte Carlo methods. The complexity is mastered by a subdivision of the full problem into a set of simpler separate tasks. All main aspects of the events are simulated, such as hard-process selection, initial- and final-state radiation, beam remnants, fragmentation, decays, and so on. Therefore events should be directly comparable with experimentally observable ones. The programs can be used to extract physics from comparisons with existing data, or to study physics at future experiments. Reasons for new version: Improved and expanded physics models. Summary of revisions: Hundreds of new features and bug fixes, allowing improved modelling. Restrictions: Depends on the problem studied. Running time: 10–1000 events per second, depending on process studied.

Pythia version 6 represents a merger of the Pythia 5, Jetset 7 and SPythia programs, with many improvements. It can be used to generate high-energy-physics ‘events’, i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions. The underlying physics is not understood well enough to give an exact description; the programs therefore contain a combination of analytical results and various models. The emphasis in this article is on new aspects, but a few words of general introduction are included. Further documentation is available on the web.

The "Snowmass Points and Slopes" (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 "Snowmass Workshop on the Future of Particle Physics" as a consensus based on different existing proposals.

A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.

This document proposes a collection of simplified models relevant to the design of new-physics searches at the LHC and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the "Topologies for Early LHC Searches" workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first ~50-500 pb-1 of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.

This document a outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. For s-channel, spin-0 and spin-1 mediations are discussed, and also realizations where the Higgs particle provides a portal between the dark and visible sectors. The guiding principles underpinning the proposed simplified models are spelled out, and some suggestions for implementation are presented.

This manual describes the Pythia event generator, the most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is most often used to generate high-energy-physics collision “events”, i.e. sets of particles produced in association with the collision of two incoming high-energy particles, but has several uses beyond that. The guiding philosophy is to produce and re-produce properties of experimentally obtained collisions as accurately as possible. The program includes a wide ranges of reactions within and beyond the Standard Model, and extending to heavy ion physics. Emphasis is put on phenomena where strong interactions play a major role. The manual contains both pedagogical and practical components. All included physics models are described in enough detail to allow the user to obtain a cursory overview of used assumptions and approximations, enabling an informed evaluation of the program output. A number of the most central algorithms are described in enough detail that the main results of the program can be reproduced independently, allowing further development of existing models or the addition of new ones. Finally, a chapter dedicated fully to the user is included towards the end, providing pedagogical examples of standard use cases, and a detailed description of a number of external interfaces. The program code, the online manual, and the latest version of this print manual can be found on the Pythia web page: https://www.pythia.org/.

This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.

We report on our exploration of matching matrix element calculations with the parton-shower models contained in the event generators HERWIG and PYTHIA. We describe results for e+e- collisions and for the hadroproduction of W bosons and Drell-Yan pairs. We compare methods based on (1) a strict implementation of ideas proposed by Catani et al., (2) a generalization based on using the internal Sudakov form factors of HERWIG and PYTHIA, and (3) a simpler proposal of M. Mangano. Where appropriate, we show the dependence on various choices of scales and clustering that do not affect the soft and collinear limits of the predictions, but have phenomenological implications. Finally, we comment on how to use these results to state systematic errors on the theoretical predictions.

In the era of precision physics measurements at the LHC, efficient and exhaustive estimations of theoretical uncertainties play an increasingly crucial role. In the context of Monte Carlo (MC) event generators, the estimation of such uncertainties traditionally requires independent MC runs for each variation, for a linear increase in total run time. In this work, we report on an automated evaluation of the dominant (renormalization-scale and nonsingular) perturbative uncertainties in the pythia 8 event generator, with only a modest computational overhead. Each generated event is accompanied by a vector of alternative weights (one for each uncertainty variation), with each set separately preserving the total cross section. Explicit scale-compensating terms can be included, reflecting known coefficients of higher-order splitting terms and reducing the effect of the variations. The formalism also allows for the enhancement of rare partonic splittings, such as $g\ensuremath{\rightarrow}b\overline{b}$ and $q\ensuremath{\rightarrow}q\ensuremath{\gamma}$, to obtain weighted samples enriched in these splittings while preserving the correct physical Sudakov factors.

The Higgs sector of the minimal supersymmetric standard model (MSSM) consists of five physical Higgs bosons, which offer a variety of channels for their experimental search. The present study aims to further our understanding of the Tevatron reach for MSSM Higgs bosons, addressing relevant theoretical issues related to the SUSY parameter space, with special emphasis on the radiative corrections to the down--quark and lepton couplings to the Higgs bosons for large $\tan\beta$. We performed a computation of the signal and backgrounds for the production processes $W\phi$ and $b \bar{b} \phi$ at the upgraded Tevatron, with $\phi$ being the neutral MSSM Higgs bosons. Detailed experimental information and further higher order calculations are demanded to confirm/refine these predictions.

We have analyzed the single $\eegg + \slashchar{E}_T$ event at CDF and found that the expected rate and kinematics are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories, where either the lightest neutralino (``neutralino LSP'' scenario) or the gravitino (``light gravitino'' scenario) is the lightest supersymmetric particle. The parameter space of the supersymmetric Lagrangian is tightly constrained by the kinematics of the event and the branching ratios for the necessary decay chain of the selectron. We identify a region of the parameter space satisfying all low-energy constraints, and consistent with the selectron interpretation of the $ee\gamma\gamma + \Et$ event. We discuss other supersymmetric processes at Fermilab Tevatron and at CERN LEP in both scenarios that could confirm or exclude a supersymmetric explanation of the event, and that could distinguish between the neutralino LSP and the light gravitino scenarios.

We analyze the prospects for discovering supersymmetry at the Fermilab Tevatron and CERN LEP colliders in the scenario that the lightest supersymmetric particle is a gravitino of mass \ensuremath{\lesssim}1 keV. We consider in particular the case that the lightest neutralino has a nearly 100% branching fraction into gravitino+photon within the detector. This implies that supersymmetric events should contain both missing (transverse) energy and two energetic photons. Therefore, one can search for supersymmetry simply through inclusive production of superpartners. We consider the exclusion and reach capabilities of the Tevatron in exploring the supersymmetric parameter space, and study the efficiencies which can be achieved in this search. We also consider the discovery reach and backgrounds at LEP with $\sqrt{s}=160, 175, \mathrm{and} 190$ GeV.

We investigate the hadron collider phenomenology of the Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation for Higgs bosons that can be observed in Standard Model search channels: W/ZH i (→ b b) at the Tevatron, and gg → H i (→ γγ), t tH i (→ b b) and W W → H i (→ τ + τ -) at the LHC.Our numerical analysis is based on a benchmark scenario proposed earlier called CPX, which has been designed to showcase the effects of CP violation in the MSSM, and on several variant benchmarks.In most of the CPX parameter space, these hadron colliders will find one of the neutral MSSM Higgs bosons.However, there are small regions of parameter space in which none of the neutral Higgs bosons can be detected in the standard channels at the Tevatron and the LHC.This occurs because the neutral Higgs boson with the largest coupling to W and Z bosons decays predominantly into either two lighter Higgs bosons or a Higgs boson and a gauge boson, whilst the lighter Higgs boson has only small couplings to the W and Z bosons and the top quark.For other choices of CP-violating parameters, all three neutral Higgs bosons can have significant couplings to W and Z bosons, producing overlapping signatures: these may or may not be distinguishable from backgrounds.The existence of these regions of parameters provides a strong motivation for a detailed experimental simulation of these channels.

This document summarises the proposal of the LHC Dark Matter Working Group on how to present LHC results on s-channel simplified dark matter models and to compare them to direct (indirect) detection experiments.

Abstract We review the main software and computing challenges for the Monte Carlo physics event generators used by the LHC experiments, in view of the High-Luminosity LHC (HL-LHC) physics programme. This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group as an input to the LHCC review of HL-LHC computing, which has started in May 2020.

Abstract In this work, we consider the case of a strongly coupled dark/hidden sector, which extends the Standard Model (SM) by adding an additional non-Abelian gauge group. These extensions generally contain matter fields, much like the SM quarks, and gauge fields similar to the SM gluons. We focus on the exploration of such sectors where the dark particles are produced at the LHC through a portal and undergo rapid hadronization within the dark sector before decaying back, at least in part and potentially with sizeable lifetimes, to SM particles, giving a range of possibly spectacular signatures such as emerging or semi-visible jets. Other, non-QCD-like scenarios leading to soft unclustered energy patterns or glueballs are also discussed. After a review of the theory, existing benchmarks and constraints, this work addresses how to build consistent benchmarks from the underlying physical parameters and present new developments for the pythia Hidden Valley module, along with jet substructure studies. Finally, a series of improved search strategies is presented in order to pave the way for a better exploration of the dark showers at the LHC.

Monte Carlo (MC) integration is an important calculational technique in the physical sciences. Practical considerations require that the calculations are performed as accurately as possible for a given set of computational resources. To improve the accuracy of MC integration, a number of useful variance reduction algorithms have been developed, including importance sampling and control variates. In this work, we demonstrate how these two methods can be applied simultaneously, thus combining their benefits. We provide a python wrapper, named CoVVVR, which implements our approach in the VEGAS program. The improvements are quantified with several benchmark examples from the literature.

Monte Carlo (MC) integration is an important calculational technique in the physical sciences. Practical considerations require that the calculations are performed as accurately as possible for a given set of computational resources. To improve the accuracy of MC integration, a number of useful variance reduction algorithms have been developed, including importance sampling and control variates. In this work, we demonstrate how these two methods can be applied simultaneously, thus combining their benefits. We provide a python wrapper, named COVVVR, which implements our approach in the VEGAS program. The improvements are quantified with several benchmark examples from the literature.

We extend the study of Higgs boson couplings in the ``golden'' $gg\ensuremath{\rightarrow}H\ensuremath{\rightarrow}Z{Z}^{*}\ensuremath{\rightarrow}4\ensuremath{\ell}$ channel in two important respects. First, we demonstrate the importance of off-shell Higgs boson production ($gg\ensuremath{\rightarrow}{H}^{*}\ensuremath{\rightarrow}ZZ\ensuremath{\rightarrow}4\ensuremath{\ell}$) in determining which operators contribute to the $HZZ$ vertex. Second, we include the five operators of lowest nontrivial dimension, including the ${Z}_{\ensuremath{\mu}}{Z}^{\ensuremath{\mu}}\ensuremath{\square}H$ and $H{Z}_{\ensuremath{\mu}}\ensuremath{\square}{Z}^{\ensuremath{\mu}}$ operators that are often neglected. We point out that the former operator can be severely constrained by the measurement of the off-shell ${H}^{*}\ensuremath{\rightarrow}ZZ$ rate and/or unitarity considerations. We provide analytic expressions for the off-peak cross sections in the presence of these five operators. On shell, the ${Z}_{\ensuremath{\mu}}{Z}^{\ensuremath{\mu}}\ensuremath{\square}H$ operator is indistinguishable from its Standard Model counterpart $H{Z}_{\ensuremath{\mu}}{Z}^{\ensuremath{\mu}}$, while the $H{Z}_{\ensuremath{\mu}}\ensuremath{\square}{Z}^{\ensuremath{\mu}}$ operator can be probed, in particular, by the ${Z}^{*}$ invariant mass distribution.

We present a quantum algorithm for implementing ${\ensuremath{\phi}}^{4}$ lattice scalar field theory on qubit computers. The field is represented in the discretized field amplitude basis. The number of qubits and elementary gates required by the implementation of the evolution operator is proportional to the lattice size. The algorithm allows efficient ${\ensuremath{\phi}}^{4}$ state preparation for a large range of input parameters in both the normal and broken-symmetry phases. The states are prepared using a combination of variational and adiabatic evolution methods. First, the ground state of a local Hamiltonian, which includes the ${\ensuremath{\phi}}^{4}$ self-interaction, is prepared using short variational circuits. Next, this state is evolved by switching on the coupling between the lattice sites adiabatically. The parameters defining the local Hamiltonian are adjustable and constitute the input of our algorithm. We present a method to optimize these parameters in order to reduce the adiabatic time required for state preparation. For preparing broken-symmetry states, the adiabatic evolution problems caused by crossing the phase transition critical line and by the degeneracy of the broken-symmetry ground state can be addressed using an auxiliary external field which gradually turns off during the adiabatic process. We show that the time dependence of the external field during the adiabatic evolution is important for addressing the broken-symmetry ground state degeneracy. The adiabatic time dependence on the inverse error tolerance can be reduced from quadratic to linear by using a field strength that decreases exponentially in time relative to one that decreases linearly.

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

We discuss the phenomenology of the lightest SU(3)_C singlet and non-singlet technihadrons in the Straw Man Model of low-scale technicolor (TCSM). The technihadrons are assumed to be those arising in topcolor--assisted technicolor models in which topcolor is broken by technifermion condensates. We improve upon the description of the color--singlet sector presented in our earlier paper introducing the TCSM (hep-ph/9903369). These improvements are most important for subprocess energies well below the masses of the technirho and techniomega, and, therefore, apply especially to e+e- colliders such as LEP and a low--energy linear collider. In the color--octet sector, we consider mixing of the gluon, the coloron V_8 from topcolor breaking, and four isosinglet color--octet technirho mesons. We assume, as expected in walking technicolor, that these technirhos decay into qbar-q, gg, and g-technipion final states, but not into technipion pairs. All the TCSM production and decay processes discussed here are included in the event generator Pythia. We present several simulations appropriate for the Tevatron Collider, and suggest benchmark model lines for further experimental investigation.

In this paper, conventional global QCD analysis is generalized to produce parton distribution functions (PDFs) optimized for use with event generators at the Large Hadron Collider (LHC). This optimization is accomplished by complementing usual constraints on the PDFs from the existing hard-scattering experimental data with those needed to reproduce cross sections for key scattering processes at the LHC, as predicted by the best available theory, in the joint input to the global analysis. With the optimized PDFs, predictions obtained by event generators at a given order in the QCD coupling strength reproduce the representative LHC cross sections computed at one higher order. In the present study, the optimized PDFs for leading-order event generators were developed. Several optimization strategies and resulting candidate PDF sets (labeled as CT09MCS, CT09MC1 and CT09MC2) are compared with those from other approaches.

The latest results from the ATLAS and CMS experiments at the CERN Large Hadron Collider unequivocally confirm the existence of a resonance X with mass near 125 GeV which could be the Higgs boson of the standard model. Measuring the properties (quantum numbers and couplings) of this resonance is of paramount importance. Initial analyses by the LHC Collaborations disfavor specific alternative benchmark hypotheses, e.g., pure pseudoscalars or gravitons. However, this is just the first step in a long-term program of detailed measurements. We consider the most general set of operators in the decay channels X→ZZ, WW, Zγ, γγ, and derive the constraint implied by the measured rate. This allows us to provide a useful parametrization of the orthogonal independent Higgs coupling degrees of freedom as coordinates on a suitably defined sphere.

We study the discovery potential of the CERN LHC, Fermilab Tevatron and CERN LEP colliders in the search for the neutral $\mathrm{CP}$-even Higgs boson of the MSSM which couples to the weak gauge bosons with a strength close to the standard model one and, hence, plays a relevant role in the mechanism of electroweak symmetry breaking. We place special emphasis on the radiative effects which influence the discovery reach of these colliders. We concentrate on the $\mathrm{Vb}\overline{b}$ channel, with $V=Z$ or W, and on the channels with diphoton final states, which are the dominant ones for the search for a light standard model Higgs boson at LEP or Tevatron and LHC, respectively. By analyzing the parameters of the MSSM for which the searches become difficult at one or more of these three colliders, we demonstrate their complementarity in the search for a light Higgs boson which plays a relevant role in the mechanism of electroweak symmetry breaking.

The decoupling properties of the Higgs sector in the minimal supersymmetric standard model (MSSM) imply that a light CP-even Higgs boson discovered at the Fermilab Tevatron or CERN LHC may closely resemble the standard model (SM) Higgs boson. In this paper, we investigate how precision measurements of Higgs properties at a linear collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson. We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle \ensuremath{\alpha} and $\mathrm{tan}\ensuremath{\beta}$-enhanced vertex corrections. The general expectation is that the Higgs couplings to ${W}^{+}{W}^{\ensuremath{-}},$ ZZ, $c\overline{c},$ and $t\overline{t}$ should quickly approach their SM values for increasing CP-odd Higgs boson mass ${m}_{A},$ while the couplings to $b\overline{b}$ and ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ do so more slowly. Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit. For a wide range of MSSM parameters, the LC is sensitive to ${m}_{A}\ensuremath{\sim}600\mathrm{GeV}$ almost independently of $\mathrm{tan}\ensuremath{\beta}.$ For large values of $\mathrm{tan}\ensuremath{\beta}$ and some specific choices of MSSM parameters [e.g., ${A}_{t}\ensuremath{\mu}<0$ and $|{A}_{t}|\ensuremath{\simeq}|\ensuremath{\mu}|\ensuremath{\simeq}\mathcal{O}{(M}_{S})$], one of the CP-even Higgs bosons can be SM-like independent of the value of ${m}_{A}.$ In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.

This is a written account of the computer tutorial offered at the Sixth MC4BSM workshop at Cornell University, March 22-24, 2012. The tools covered during the tutorial include: FeynRules, LanHEP, MadGraph, CalcHEP, Pythia 8, Herwig++, and Sherpa. In the tutorial, we specify a simple extension of the Standard Model, at the level of a Lagrangian. The software tools are then used to automatically generate a set of Feynman rules, compute the invariant matrix element for a sample process, and generate both parton-level and fully hadronized/showered Monte Carlo event samples. The tutorial is designed to be self-paced, and detailed instructions for all steps are included in this write-up. Installation instructions for each tool on a variety of popular platforms are also provided.

The production rate and kinematic distributions of isolated photon pairs produced in hadron interactions are studied. The effects of the initial-state multiple soft-gluon emission to the scattering subprocesses $q\overline{q},qg,$ and $g\stackrel{\ensuremath{\rightarrow}}{g}\ensuremath{\gamma}\ensuremath{\gamma}X$ are resummed with the Collins-Soper-Sterman soft gluon resummation formalism. The effects of fragmentation photons from $q\stackrel{\ensuremath{\rightarrow}}{g}\ensuremath{\gamma}q,$ followed by $\stackrel{\ensuremath{\rightarrow}}{q}\ensuremath{\gamma}X,$ are also studied. The results are compared with data from the Fermilab Tevatron collider. A prediction of the production rate and kinematic distributions of the diphoton pair in proton-nucleon reactions is also presented.

The resummation of multiple soft gluon emission affects the kinematic distributions of W+h (where h is a Higgs boson) and tb̄ pairs at hadron colliders. Using the Collins–Soper–Sterman resummation formalism, various kinematic distributions of the individual final state particles and the pair are calculated for the W+h process, with a Higgs boson mass between 80–120 GeV, and the tb̄ process, with mt between 170–180 GeV. We also estimate part of the higher order (beyond next-to-leading order) effect to their production rates.

SPYTHIA is an event level Monte Carlo program which simulates particle production and decay at lepton and hadron colliders in the Minimal Supersymmetric Standard Model (MSSM). It is an extension of PYTHIA 5.7, with all of its previous capabilities. This paper is meant to supplement the PYTHIA/JETSET user manual, providing a description of the new particle spectrum, hard scattering processes, and decay modes. Several examples of using the program are provided.

Z' bosons that couple preferentially to the third generation fermions can arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1)) gauge groups. We show that existing limits on quark-lepton compositeness set by the LEP and Tevatron experiments translate into lower bounds of order a few hundred GeV on the masses of these Z' bosons. Resonances of this mass can be directly produced at the Tevatron. Accordingly, we explore in detail the limits that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We also comment on the possibility of using hadronically-decaying taus to improve the limits.

Theories of new physics often involve a large number of unknown parameters which need to be scanned. Additionally, a putative signal in a particular channel may be due to a variety of distinct models of new physics. This makes experimental attempts to constrain the parameter space of motivated new physics models with a high degree of generality quite challenging. We describe how the reweighting of events may allow this challenge to be met, as fully simulated Monte Carlo samples generated for arbitrary benchmark models can be effectively re-used. In particular, we suggest procedures that allow more efficient collaboration between theorists and experimentalists in exploring large theory parameter spaces in a rigorous way at the LHC.

This document summarises the proposal of the LHC Dark Matter Working Group on how to present LHC results on s-channel simplified dark matter models and to compare them to direct (indirect) detection experiments.

For some choices of soft supersymmetry (SUSY)-breaking parameters, the lightest supersymmetric particle (LSP) is a stable neutralino ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0},$ the NLSP is a chargino ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ almost degenerate in mass with the LSP $(\ensuremath{\Delta}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}}\ensuremath{\equiv}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{-}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}}\ensuremath{\sim}{m}_{\ensuremath{\pi}}\ensuremath{-}\mathrm{few}\mathrm{}\mathrm{GeV}),$ and all other sparticles are relatively heavy. In this case, detection of sparticles in the usual, supergravity (MSUGRA)-motivated signals will be difficult, since the decay products in ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}\dots{}$ will be very soft, and alternative signals must be considered. Here, we study the viability of signatures at the Fermilab Tevatron based on highly ionizing charged tracks, disappearing charged tracks, large impact parameters, missing transverse energy, and a jet or a photon, and determine the mass reach of such signatures assuming that only the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}$ are light. We also consider the $\mathrm{jet}+{E}_{T}$ and $\ensuremath{\gamma}+{E}_{T}$ signatures assuming that the gluino is also light with ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}\ensuremath{\sim}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}.$ We find that the mass reach is critically dependent upon $\ensuremath{\Delta}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}}$ and ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}\ensuremath{-}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}.$ If $\ensuremath{\Delta}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}}$ is sufficiently big that $c\ensuremath{\tau}({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}})\ensuremath{\lesssim}\mathrm{few}\mathrm{}\mathrm{cm}$ and ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}$ is large, there is a significant possibility that the limits on ${m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}$ based on CERN LEP2 data cannot be extended at the Fermilab Tevatron. If $c\ensuremath{\tau}({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}})>\mathrm{few}\mathrm{}\mathrm{cm},$ relatively background-free signals exist that will give a clear signal of ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ production (for some range of ${m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}})$ even if ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}$ is very large.

Generic Fortran common blocks are presented for use by High Energy Physics event generators for the transfer of event configurations from parton level generators to showering and hadronization event generators.

Recently published benchmark models have contained rather heavy superpartners. To test the robustness of this result, several benchmark models have been constructed based on theoretically well-motivated approaches, particularly string-based ones. These include variations on anomaly- and gauge-mediated models, as well as gravity mediation. The resulting spectra often have light gauginos that are produced in significant quantities at the Fermilab Tevatron collider, or will be at a 500 GeV linear collider. The signatures also provide interesting challenges for the CERN LHC. In addition, these models are capable of accounting for electroweak symmetry breaking with less severe cancellations among soft supersymmetry breaking parameters than previous benchmark models.

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

We study the most promising signals of Constrained Minimal Supersymmetry detectable at a luminosity upgraded 2 TeV Fermilab Tevatron collider. Using a full event-level Monte Carlo based on Pythia/Jetset, we simulate the trilepton signal examining in detail the effect of constraints on the parameter space. We also simulate the monolepton and dilepton signals, the missing E_T + jets signal, and the signals of stop production in supersymmetry all with full Standard Model backgrounds with realistic detector cuts. We find that large fractions of parameter space can be probed (or eliminated if no signal is found), but mass limits on charginos and neutralinos are not possible based solely on the trilepton signal. Detection efficiencies depend strongly on supersymmetry parameters beyond simply the neutralino and chargino masses; analyses (experimental or theoretical) that do not include this will draw misleading conclusions. Finally, we comment on how searches at LEP II will complement searches at Fermilab.

APPRENTICE is a tool developed for event generator tuning. It contains a range of conceptual improvements and extensions over the tuning tool Professor. Its core functionality remains the construction of a multivariate analytic surrogate model to computationally expensive Monte-Carlo event generator predictions. The surrogate model is used for numerical optimization in chi-square minimization and likelihood evaluation. Apprentice also introduces algorithms to automate the selection of observable weights to minimize the effect of mis-modeling in the event generators. We illustrate our improvements for the task of MC-generator tuning and limit setting.

We discuss and illustrate the properties of several parton-shower algorithms available in Pythia and Vincia, in the context of Higgs production via vector boson fusion (VBF). In particular, the distinctive colour topology of VBF processes allows to define observables sensitive to the coherent radiation pattern of additional jets. We study a set of such observables, using the Vincia sector-antenna shower as our main reference, and contrast it to Pythia's transverse-momentum-ordered DGLAP shower as well as Pythia's dipole-improved shower. We then investigate the robustness of these predictions as successive levels of higher-order perturbative matrix elements are incorporated, including next-to-leading-order matched and tree-level merged calculations, using Powheg Box and Sherpa respectively to generate the hard events.

Quantum simulation of quantum field theory is a flagship application of quantum computers that promises to deliver capabilities beyond classical computing. The realization of quantum advantage will require methods to accurately predict error scaling as a function of the resolution and parameters of the model that can be implemented efficiently on quantum hardware. In this paper, we address the representation of lattice bosonic fields in a discretized field amplitude basis, develop methods to predict error scaling, and present efficient qubit implementation strategies. A low-energy subspace of the bosonic Hilbert space, defined by a boson occupation cutoff, can be represented with exponentially good accuracy by a low-energy subspace of a finite size Hilbert space. The finite representation construction and the associated errors are directly related to the accuracy of the Nyquist-Shannon sampling and the Finite Fourier transforms of the boson number states in the field and the conjugate-field bases. We analyze the relation between the boson mass, the discretization parameters used for wavefunction sampling and the finite representation size. Numerical simulations of small size $\Phi^4$ problems demonstrate that the boson mass optimizing the sampling of the ground state wavefunction is a good approximation to the optimal boson mass yielding the minimum low-energy subspace size. However, we find that accurate sampling of general wavefunctions does not necessarily result in accurate representation. We develop methods for validating and adjusting the discretization parameters to achieve more accurate simulations.

We present a refined and expanded analysis of the CDF $ee\gamma\gamma + \Et$ event as superpartner production, assuming the lightest neutralino is the lightest supersymmetric particle. A general low-energy Lagrangian is constrained by a minimum cross section times branching ratio into two electrons and two photons, kinematics consistent with the event, and LEP1-LEP130 data. We examine how the supersymmetric parameters depend on the kinematics, branching ratios and experimental predictions with a selectron interpretation of the event, and discuss to what extent these are modified by other interpretations. Predictions for imminent CERN LEP upgrades and the present and future Fermilab Tevatron are presented. Finally, we briefly discuss the possible connection to other phenomena including a light stop, the neutralino relic density, the shift in $R_b$ and the associated shift in $\alpha_s$, and implications for the form of the theory.

We argue that it is possible to make a consistent picture of Fermilab data including the production and decay of gluinos and squarks. Assuming the stop squark mass is small enough, about half of the top quarks decay to stop squarks, and the loss of standard model top quark pair production rate is compensated by the supersymmetric processes. This behavior is consistent with the reported top quark decay data and suggests several other possible decay signatures. This picture can be tested easily with more data, perhaps even with the data in hand. It also has implications for the top mass measurement and the interpretation of the CERN ${e}^{+}{e}^{\ensuremath{-}}$ collider LEP ${R}_{b}$ excess.

We analyze the prospects of the Tevatron for finding a Higgs boson in the two photon decay mode. We conclude that the Standard Model (SM) Higgs boson will likely not be discovered in this mode. However, we motivate several theories beyond the SM, including the MSSM, that predict a Higgs boson with enhanced branching fractions into photons, and calculate the luminosity needed to discover a general Higgs boson at the Tevatron by a two-photon invariant mass peak at large transverse momentum. We find that a high luminosity Tevatron will play a significant role in discovering or constraining these theories.

We combine results from CDF and D0 on direct searches for the standard model (SM) Higgs boson H in ppbar collisions at the Fermilab Tevatron at sqrt(s)=1.96 TeV. Compared to the previous Tevatron Higgs search combination more data have been added, additional new channels have been incorporated, and some previously used channels have been reanalyzed to gain sensitivity. We use the latest parton distribution functions and gg to H theoretical cross sections when comparing our limits to the SM predictions. With up to 5.9 fb-1 of data analyzed at CDF, and up to 6.7 fb-1 at D0, the 95% C.L. upper limits on Higgs boson production are factors of 1.56 and 0.68 the values of the SM cross section for a Higgs boson mass of m_H=115 GeV/c^2 and 165~GeVc^2. We exclude, at the 95% C.L., a new and larger region at high mass between 158

Abstract Measurements of quarkonia isolation in jets at the Large Hadron Collider (LHC) have been shown to disagree with fixed-order non-relativistic quantum chromodynamics (NRQCD) calculations, even at higher orders. Calculations using the fragmenting jet function formalism are able to better describe data but cannot provide full event-level predictions. In this work we provide an alternative model via NRQCD production of quarkonia in a timelike parton shower. We include this model in the Pythia 8 event generator and validate our parton-shower implementation against analytic forms of the relevant fragmentation functions. Finally, we make inclusive predictions of quarkonia production for the decay of the standard-model Higgs boson.

We review recent suggestions to quantum simulate scalar electrodynamics (the lattice Abelian Higgs model) in 1 + 1 dimensions with rectangular arrays of Rydberg atoms.We show that platforms made publicly available recently allow empirical explorations of the critical behavior of quantum simulators.We discuss recent progress regarding the phase diagram of two-leg ladders, effective Hamiltonian approaches and the construction of hybrid quantum algorithms targeting hadronization in collider physics event generators.

The decoupling properties of the Higgs sector in the Minimal Supersymmetric Standard Model (MSSM) imply that a light CP-even Higgs boson discovered at the Tevatron or LHC may closely resemble the Standard Model (SM) Higgs boson.In this paper, we investigate how precision measurements of Higgs properties at a Linear Collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson.We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle α and tan β-enhanced vertex corrections.The general expectation is that the Higgs couplings to W + W -, ZZ, cc and t t should quickly approach their SM values for increasing CP-odd Higgs mass m A , while the couplings to b b and τ + τ -do so more slowly.Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit.For a wide range of MSSM parameters, the LC is sensitive to m A ∼ 600 GeV almost independently of tan β.For large values of tan β and some specific choices of MSSM parameters [e.g., A t µ < 0 and |A t | ≃ |µ| ≃ O(M S )], one of the CP-even Higgs bosons can be SM-like independent of the value of m A .In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.

This Report summarizes the proceedings of the 2019 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments for high precision Standard Model calculations, (II) the sensitivity of parton distribution functions to the experimental inputs, (III) new developments in jet substructure techniques and a detailed examination of gluon fragmentation at the LHC, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, and (V) Monte Carlo event generator studies relating to PDF evolution and comparisons of important processes at the LHC.

This Resource Book reviews the physics opportunities of a next-generation e+e- linear collider and discusses options for the experimental program. Part 1 contains the table of contents and introduction and gives a summary of the case for a 500 GeV linear collider.

We describe a coherent strategy and set of tools for reconstructing the fundamental theory of the TeV scale from LHC data. We show that On-Shell Effective Theories (OSETs) effectively characterize hadron collider data in terms of masses, production cross sections, and decay modes of candidate new particles. An OSET description of the data strongly constrains the underlying new physics, and sharply motivates the construction of its Lagrangian. Simulating OSETs allows efficient analysis of new-physics signals, especially when they arise from complicated production and decay topologies. To this end, we present MARMOSET, a Monte Carlo tool for simulating the OSET version of essentially any new-physics model. MARMOSET enables rapid testing of theoretical hypotheses suggested by both data and model-building intuition, which together chart a path to the underlying theory. We illustrate this process by working through a number of data challenges, where the most important features of TeV-scale physics are reconstructed with as little as 5 fb{sup -1} of simulated LHC signals.

The increasing use of multivariate methods, and in particular the Matrix Element Method (MEM), represents a revolution in experimental particle physics. With continued exponential growth in computing capabilities, the use of sophisticated multivariate methods-- already common-- will soon become ubiquitous and ultimately almost compulsory. While the existence of sophisticated algorithms for disentangling signal and background might naively suggest a diminished role for theorists, the use of the MEM, with its inherent connection to the calculation of differential cross sections will benefit from collaboration between theorists and experimentalists. In this white paper, we will briefly describe the MEM and some of its recent uses, note some current issues and potential resolutions, and speculate about exciting future opportunities.

We present two approaches for computing rational approximations to multivariate functions, motivated by their effectiveness as surrogate models for high-energy physics (HEP) applications. Our first approach builds on the Stieltjes process to efficiently and robustly compute the coefficients of the rational approximation. Our second approach is based on an optimization formulation that allows us to include structural constraints on the rational approximation (in particular, constraints demanding the absence of singularities), resulting in a semi-infinite optimization problem that we solve using an outer approximation approach. We present results for synthetic and real-life HEP data, and we compare the approximation quality of our approaches with that of traditional polynomial approximations.

We study the possibility of discovering or excluding a light top squark (stop) t̃1 based on top quark decays in the tt events produced at the Fermilab Tevatron. In particular, we consider the Minimal Supersymmetric Standard Model with the sparticle spectrum mχ1± + mb, Mw + mχ10 + mb > mt̃1 > mχ10 + mc, where χ10 is the lightest neutralino, so that t → t̃1χ10 and t̃1 → cχ10. All other sparticle masses are assumed to be heavier than mt. Such a spectrum seeks to explain the experimental values of αs(Mz2), Rb and Alr obtained from LEP/SLC data. We find that the prospect to observe a light stop via channel at the Tevatron is very promising.

We report on a method for matching the next-to-leading order calculation of QCD jet production in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation with a Monte Carlo parton shower event generator (MC) to produce realistic final states. The final result is accurate to next-to-leading order (NLO) for infrared-safe one-scale quantities, such as the Durham 3-jet fraction ${y}_{3}$, and agrees well with parton shower results for multiscale quantities, such as the jet mass distribution in 3-jet events. For our numerical results, the NLO calculation is matched to the event generator Pythia, though the method is more general. We compare one-scale and multiscale quantities from pure NLO, pure MC, and matched NLO-MC calculations.

The experiments at Run 2 of the Tevatron have each accumulated over 1 inverse femtobarn of high-transverse momentum data. Such a dataset allows for the first precision (i.e. comparisons between theory and experiment at the few percent level) tests of QCD at a hadron collider. While the Large Hadron Collider has been designed as a discovery machine, basic QCD analyses will still need to be performed to understand the working environment. The Tevatron-for-LHC workshop was conceived as a communication link to pass on the expertise of the Tevatron and to test new analysis ideas coming from the LHC community. The TeV4LHC QCD Working Group focussed on important aspects of QCD at hadron colliders: jet definitions, extraction and use of Parton Distribution Functions, the underlying event, Monte Carlo tunes, and diffractive physics. This report summarizes some of the results achieved during this workshop.

Combined results are presented on the search for a neutral Higgs boson in the di-tau final state using 1.8 fb{sup -1} and 2.2 fb{sup -1} of integrated luminosity collected at the CDF and D0 experiments respectively. Data were collected in p{bar p} collisions at a centre of mass energy of 1.96 TeV during RunII of the Tevatron. Limits are set on the cross section x branching ratio ranging from 13.6 pb to 0.653 pb for Higgs masses from 90 GeV to 200 GeV respectively. The results are then interpreted as limits in four different benchmark scenarios within the framework of the MSSM.

We present an analysis of the discovery reach for supersymmetric particles at the upgraded Tevatron collider, assuming that SUSY breaking results in universal soft breaking parameters at the grand unification scale, and that the lightest supersymmetric particle is stable and neutral. We first present a review of the literature, including the issues of unification, renormalization group evolution of the supersymmetry breaking parameters and the effect of radiative corrections on the effective low energy couplings and masses of the theory. We consider the experimental bounds coming from direct searches and those arising indirectly from precision data, cosmology and the requirement of vacuum stability. The issues of flavor and CP-violation are also addressed. The main subject of this study is to update sparticle production cross sections, make improved estimates of backgrounds, delineate the discovery reach in the supergravity framework, and examine how this might vary when assumptions about universality of soft breaking parameters are relaxed. With 30 fb$^{-1}$ luminosity and one detector, charginos and neutralinos, as well as third generation squarks, can be seen if their masses are not larger than 200-250 GeV, while first and second generation squarks and gluinos can be discovered if their masses do not significantly exceed 400 GeV. We conclude that there are important and exciting physics opportunities at the Tevatron collider, which will be significantly enhanced by continued Tevatron operation beyond the first phase of Run II.

The search for Higgs bosons in both the standard model and its extensions is well under way at the Tevatron. As the integrated luminosity collected increases into the multiple inverse femptobarn range, these searches are becoming very interesting indeed. Meanwhile, the construction of the Large Hadron Collider (LHC) and its associated experiments at CERN are nearing completion. In this TeV4LHC workshop, it was realized that any experience at the Tevatron with respect to backgrounds, experimental techniques and theoretical calculations that can be verified at the Tevatron which have relevance for future measurements at the LHC were important. Studies and contributions to these efforts were made in three broad categories: theoretical calculations of Higgs production and decay mechanisms; theoretical calculations and discussions pertaining to non-standard model Higgs bosons; and experimental reviews, analyses and developments at both the Tevatron and the upcoming LHC experiments. All of these contributions represent real progress towards the elucidation of the mechanism of electroweak symmetry breaking.

We propose an intuitive, machine-learning approach to multiparameter inference, dubbed the InferoStatic Networks (ISN) method, to model the score and likelihood ratio estimators in cases when the probability density can be sampled but not computed directly. The ISN uses a backend neural network that models a scalar function called the inferostatic potential \varphi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>φ</mml:mi></mml:math> . In addition, we introduce new strategies, respectively called Kernel Score Estimation (KSE) and Kernel Likelihood Ratio Estimation (KLRE), to learn the score and the likelihood ratio functions from simulated data. We illustrate the new techniques with some toy examples and compare to existing approaches in the literature. We mention en passant some new loss functions that optimally incorporate latent information from simulations into the training procedure.

We propose an intuitive, machine-learning approach to multiparameter inference, dubbed the InferoStatic Networks (ISN) method, to model the score and likelihood ratio estimators in cases when the probability density can be sampled but not computed directly. The ISN uses a backend neural network that models a scalar function called the inferostatic potential \varphi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>φ</mml:mi></mml:math> . In addition, we introduce new strategies, respectively called Kernel Score Estimation (KSE) and Kernel Likelihood Ratio Estimation (KLRE), to learn the score and the likelihood ratio functions from simulated data. We illustrate the new techniques with some toy examples and compare to existing approaches in the literature. We mention en passant some new loss functions that optimally incorporate latent information from simulations into the training procedure.

This work reports on a method for uncertainty estimation in simulated collider-event predictions. The method is based on a Monte Carlo-veto algorithm, and extends previous work on uncertainty estimates in parton showers by including uncertainty estimates for the Lund string-fragmentation model. This method is advantageous from the perspective of simulation costs: a single ensemble of generated events can be reinterpreted as though it was obtained using a different set of input parameters, where each event now is accompanied with a corresponding weight. This allows for a robust exploration of the uncertainties arising from the choice of input model parameters, without the need to rerun full simulation pipelines for each input parameter choice. Such explorations are important when determining the sensitivities of precision physics measurements. Accompanying code is available at https://gitlab.com/uchep/mlhad-weights-validation.

Abstract We discuss the role of matrix element corrections (MEC) to parton showers in the context of MC@NLO-type matchings for processes that feature unstable resonances, where MEC are liable to result in double-counting issues, and are thus generally not employed. By working with Pythia8 , we show that disabling all MEC is actually unnecessary in computations based on the narrow-width approximation, and we propose alternative MEC settings which, while still avoiding double counting, allow one to include hard-recoil effects in the simulations of resonance decays. We illustrate our findings by considering $$t\bar{t}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>t</mml:mi> <mml:mover> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> </mml:math> production at the LHC, and by comparing MadGraph5-aMC@NLO predictions with those of POWHEG-BOX and standalone Pythia8 .

For some choices of soft supersymmetry-breaking parameters, the lighest supersymmetric particle is a stable neutralino ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}$ that is almost degenerate in mass with the lightest chargino ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ $(\ensuremath{\Delta}{m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}\ensuremath{\equiv}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{-}{m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}}\ensuremath{\sim}{m}_{\ensuremath{\pi}}\ensuremath{-}\mathrm{few}\mathrm{}\mathrm{GeV}),$ and all other sparticles are relatively heavy. We discuss the potential of a $\sqrt{s}\ensuremath{\sim}600\mathrm{GeV}$ ${e}^{+}{e}^{\ensuremath{-}}$ collider for studying such models.

Once superpartners are discovered at colliders, the next challenge will be to determine the parameters of the supersymmetric Lagrangian. We illustrate how the relative phases of the gluino, SU(2), and U(1) gauginos and the Higgsino mass parameter μ can be measured at a hadron collider without ad hoc assumptions about the underlying physics, focusing on Fermilab. We also discuss how the gluino and LSP masses can be measured.

This report reviews the properties of Higgs bosons in the Standard Model (SM) and its various extensions. We give an extensive overview about the potential of the ILC operated at centre-of-mass energies up to 1 TeV (including the gamma gamma option) for the determination of the Higgs boson properties. This comprises the measurement of the Higgs boson mass, its couplings to SM fermions and gauge bosons, and the determination of the spin and the CP quantum numbers of the Higgs. The extensions of the SM that are analyzed in more detail are heavy SM-like Higgs bosons, heavy Higgs bosons in the framework of Supersymmetry (SUSY) and further exotic scenarios. We review recent theoretical developments in the field of Higgs boson physics. The important question what the ILC can contribute to Higgs boson physics after the LHC, the LHC/ILC interplay and synergy is discussed. The impact of Higgs boson physics on cosmology in several SUSY frameworks is analyzed. The impact of the accelerator and dector performance on the precision of measurements are discussed in detail. We propose a strategy to optimize future analyses. Open questions arising for the various topics are listed, further topics of study and corresponding roadmaps are suggested.

This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.

Generic Fortran common blocks are presented for use by High Energy Physics event generators for the transfer of event configurations from parton level generators to showering and hadronization event generators.

This Report documents the results obtained by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of uncertainties in Parton Distribution Functions is reviewed. Progresses in the description of multiparton final states at Next-to-Leading Order and the extension of calculations for precision QCD observables beyond this order are summarized. Various issues concerning the relevance of resummation for observables at TeV colliders is examined. Improvements to algorithms of jet reconstruction are discussed and predictions for diphoton and photon pi-zero production at the LHC are made for kinematic variables of interest regarding searches for a Higgs boson decaying into two photons. Finally, several improvements implemented in Monte-Carlo event generators are documented.

We combine results from CDF and D0's direct searches for the standard model (SM) Higgs boson (H) produced in p{bar p} collisions at the Fermilab Tevatron at {radical}s = 1.96 TeV. The results presented here include those channels which are most sensitive to Higgs bosons with mass between 130 and 200 GeV/c{sup 2}, namely searches targeted at Higgs boson decays to W{sup +}W{sup -}, although acceptance for decays into {tau}{sup |+} {tau}{sup -} and {gamma}{gamma} is included. Compared to the previous Tevatron Higgs search combination, more data have been added and the analyses have been improved to gain sensitivity. We use the MSTW08 parton distribution functions and the latest gg {yields} H theoretical cross section predictions when testing for the presence of a SM Higgs boson. With up to 7.1 fb{sup -1} of data analyzed at CDF, and up to 8.2 fb{sup -1} at D0, the 95% C.L. upper limits on Higgs boson production is a factor of 0.54 times the SM cross section for a Higgs boson mass of 165 GeV/c{sup 2}. We exclude at the 95% C.L. the region 158 < m{sub H} < 173 GeV/c{sup 2}.

The parameters in Monte Carlo (MC) event generators are tuned on experimental measurements by evaluating the goodness of fit between the data and the MC predictions. The relative importance of each measurement is adjusted manually in an often time-consuming, iterative process to meet different experimental needs. In this work, we introduce several optimization formulations and algorithms with new decision criteria for streamlining and automating this process. These algorithms are designed for two formulations: bilevel optimization and robust optimization. Both formulations are applied to the datasets used in the ATLAS A14 tune and to the dedicated hadronization datasets generated by the SHERPA generator, respectively. The corresponding tuned generator parameters are compared using three metrics. We compare the quality of our automatic tunes to the published ATLAS A14 tune. Moreover, we analyze the impact of a pre-processing step that excludes data that cannot be described by the physics models used in the MC event generators.

The "golden" channel, in which the newly-discovered Higgs boson decays to four leptons by means of intermediate vector bosons, is important for determining the properties of the Higgs boson and for searching for subtle new physics effects. Different approaches exist for parametrizing the relevant Higgs couplings in this channel; here we relate the use of pseudo-observables to methods based on specifying the most general amplitude or Lagrangian terms for the $HVV$ interactions. We also provide projections for sensitivity in this channel in several novel scenarios, illustrating the use of pseudo-observables, and analyze the role of kinematic distributions and (ratios of) rates in such $H\to4\ell$ studies.

The discovery of the top-quark and the analysis of its decay products is an important test of the standard model. We consider the effects of final-state QCD radiation on the determination of the top-quark mass for $t\overline{t}$ pairs produced at the Superconducting Super Collider, CERN Large Hadron Collider, and Fermilab Tevatron. We also examine the polarization of the $W$ boson produced from a heavy-top-quark decay. We calculate the rate for gluon bremsstrahlung in the charged-current decay $t\ensuremath{\rightarrow}b{W}^{+}g$ of a heavy top quark. The effect of $b$ tagging and jet definition on the determination of these observables is discussed.

In some composite models of quarks and leptons, leptons are expected to develop strong interactions at high energies. This hypothesis can be tested by studying the absorption of high-energy particles emitted by point sources in the sky on the cosmic microwave background. Data on Cygnus X-3 exhibit an anomaly in the absorption. A plausible interpretation of the anomaly is that some of the interactions are caused by neutrinos. We infer that the cross section of neutrino-nucleon interactions is approximately 6 mb at energies of a few PeV, significantly exceeding the prediction of the standard model.

tolerances, with standard drift chamber resolutions ({approximately} 100{mu}m), and with no reliance on the performance of an inner tracking system. Robustness is provided by additional momentum measurements in the inner tracker and in a solid iron spectrometer utilizing the magnet`s return yoke. The total cost of the system, including proper magnetic shielding for the magnet and a forward-backward iron-core toroid muon detection system with {Delta}p/p {approx_equal} 9%, is comparable to that of the low-field L*/GEM approach that does not provide a magnetic flux return nor a forward-backward iron system. The magnet leaves the same amount of space for inner detector items as does the large, low-field L*-type system, while providing a substantially higher magnetic field in the inner tracking volume.

The authors review the status of searches for supersymmetric particles at the Tevatron collider. After discussing the theoretical aspects relevant to the production and decay of supersymmetric particles at the Tevatron, the authors present the current results for runs Ia and Ib as of the summer of 1997.

We combine results from CDF and D0's direct searches for the standard model (SM) Higgs boson (H) produced in ppbar collisions at the Fermilab Tevatron at sqrt{s}=1.96 TeV, focusing on the decay H\rightarrow\gamma\gamma. We compute upper limits on the Higgs boson production cross section times the decay branching fraction in the range 100

Common and community software packages, such as ROOT, Geant4 and event generators have been a key part of the LHC's success so far and continued development and optimisation will be critical in the future. The challenges are driven by an ambitious physics programme, notably the LHC accelerator upgrade to high-luminosity, HL-LHC, and the corresponding detector upgrades of ATLAS and CMS. In this document we address the issues for software that is used in multiple experiments (usually even more widely than ATLAS and CMS) and maintained by teams of developers who are either not linked to a particular experiment or who contribute to common software within the context of their experiment activity. We also give space to general considerations for future software and projects that tackle upcoming challenges, no matter who writes it, which is an area where community convergence on best practice is extremely useful.

This report reviews the properties of Higgs bosons in the Standard Model (SM) and its various extensions. We give an extensive overview of the potential of the ILC operated at center-ofmass energies up to 1 TeV (including the γγ collider option) for the determination of the Higgs boson properties. This includes the measurement of the Higgs boson mass, its couplings to SM fermions and gauge bosons, and the determination of the spin and the CP quantum numbers of the Higgs. We also discuss extensions of the SM, including heavy SM-like Higgs bosons, heavy Higgs bosons in the framework of Supersymmetry (SUSY) and more exotic scenarios. We review recent theoretical developments in the field of Higgs boson physics, and the impact of Higgs boson physics on cosmology in several SUSY frameworks is considered. The important questions as to what the ILC can contribute to Higgs boson physics after the LHC, the LHC/ILC interplay and synergy, are addressed. The impact of the accelerator and detector performance on the precision of measurements are discussed in detail and we propose a strategy to optimize future analyses. Open questions arising for the various topics are listed, and further topics of study and corresponding roadmaps are suggested.

We study the kinematic distributions of top--antitop quark pairs produced at the Tevatron, including the effects of initial state and final state multiple soft gluon emission, using the Collins--Soper--Sterman resummation formalism. The resummed results are compared with those predicted by the showering event generator PYTHIA for various distributions involving the top--antitop quark pair and the individual top quark or antiquark. The comparison between the experimental and predicted distributions will be a strong test of our understanding and application of perturbative QCD. Our results indicate that the showering event generators do not produce enough radiation. We reweight the PYTHIA distributions to agree with our resummed calculation, then use the reweighted events to better estimate the true hadronic activity in top--antitop quark pair production at hadron colliders.

This is the TeV4LHC report of the Physics Landscapes Working Group, focused on facilitating the start-up of physics explorations at the LHC by using the experience gained at the Tevatron. We present experimental and theoretical results that can be employed to probe various scenarios for physics beyond the Standard Model.

This document summarises the proposal of the LHC Dark Matter Working Group on how to present LHC results on $s$-channel simplified dark matter models and to compare them to direct (indirect) detection experiments.

The simple "straw-man" model of low-scale technicolor contains light color--singlet technihadrons, which mix with the electroweak gauge bosons. We present lepton collider production rates at the parton level, and show that experiments at LEP2 may be sensitive to the presence of technirho and techniomega states with masses 10-20 GeV beyond the center-of-mass energy because of the mixing. The exact sensitivity depends on several parameters, such as the technipion mass, the technipion mixing angle, and the charge of the technifermions. In an appendix, we describe the implementation of the model into the event generator PYTHIA for particle-level studies at lepton and hadron colliders.

This Resource Book reviews the physics opportunities of a next-generation e+e- linear collider and discusses options for the experimental program. Part 4 discusses options for the linear collider program, at a number of levels. First, it presents a broad review of physics beyond the Standard Model, indicating how the linear collider is relevant to each possible pathway. Next, it surveys options for the accelerator and experimental plan, including the questions of the running scenario, the issue of one or two interaction regions, and the options for positron polarization, photon-photon collisions, and e-e- collisions. Finally, it reviews the detector design issues for the linear collider and presents three possible detector designs.

Lepton collider experiments can search for light technipions in final states made striking by the presence of an energetic photon: $e+e- \to \photon\technipion$. To date, searches have focused on either production through anomalous coupling of the technipions to electroweak gauge bosons or on production through a technivector meson (\technirho, \techniomega) resonance. This paper creates a combined framework in which both contributions are included. This will allow stronger and more accurate limits on technipion production to be set using existing data from LEP or future data from a higher-energy linear collider. We provide explicit formulas and sample calculations (analytic and Pythia) in the framework of the Technicolor Straw Man Model, a model that includes light technihadrons.

We combine results from searches by the CDF and D0 Collaborations for a standard model Higgs boson (H) in the processes gg {yields} H {yields} W{sup +}W{sup -} and gg {yields} H {yields} ZZ in p{bar p} collisions at the Fermilab Tevatron Collider at {radical}s = 1.96 TeV. With 8.2 fb{sup -1} of integrated luminosity analyzed at CDF and 8.1 fb{sup -1} at D0, the 95% C.L. upper limit on {sigma}(gg {yields} H) x {Beta}(H {yields} W{sup +}W{sup -}) is 1.01 pb at m{sub H} = 120 GeV, 0.40 pb at m{sub H} = 165 GeV, and 0.47 pb at m{sub H} = 200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% Confidence Level a standard-model-like Higgs boson with a mass between 124 and 286 GeV.

We discuss the role of matrix element corrections (MEC) to parton showers in the context of MC@NLO-type matchings for processes that feature unstable resonances, where MEC are liable to result in double-counting issues, and are thus generally not employed. By working with Pythia8, we show that disabling all MEC is actually unnecessary in computations based on the narrow-width approximation, and we propose alternative MEC settings which, while still avoiding double counting, allow one to include hard-recoil effects in the simulations of resonance decays. We illustrate our findings by considering top-antitop production at the LHC, and by comparing MadGraph_aMC@NLO predictions with those of POWHEG-BOX and standalone Pythia8.

Monte Carlo (MC) integration is an important calculational technique in the physical sciences. Practical considerations require that the calculations are performed as accurately as possible for a given set of computational resources. To improve the accuracy of MC integration, a number of useful variance reduction algorithms have been developed, including importance sampling and control variates. In this work, we demonstrate how these two methods can be applied simultaneously, thus combining their benefits. We provide a python wrapper, named CoVVVR, which implements our approach in the Vegas program. The improvements are quantified with several benchmark examples from the literature.

We introduce a model of hadronization based on invertible neural networks that faithfully reproduces a simplified version of the Lund string model for meson hadronization. Additionally, we introduce a new training method for normalizing flows, termed MAGIC, that improves the agreement between simulated and experimental distributions of high-level (macroscopic) observables by adjusting single-emission (microscopic) dynamics. Our results constitute an important step toward realizing a machine-learning based model of hadronization that utilizes experimental data during training. Finally, we demonstrate how a Bayesian extension to this normalizing-flow architecture can be used to provide analysis of statistical and modeling uncertainties on the generated observable distributions.

Measurements of quarkonia isolation in jets at the Large Hadron Collider (LHC) have been shown to disagree with fixed-order non-relativistic quantum chromodynamics (NRQCD) calculations, even at higher orders. Calculations using the fragmenting jet function formalism are able to better describe data but cannot provide full event-level predictions. In this work we provide an alternative model via NRQCD production of quarkonia in a timelike parton shower. We include this model in the Pythia 8 event generator and validate our parton-shower implementation against analytic forms of the relevant fragmentation functions. Finally, we make inclusive predictions of quarkonia production for the decay of the standard-model Higgs boson.

We review recent suggestions to quantum simulate scalar electrodynamics (the lattice Abelian Higgs model) in $1+1$ dimensions with rectangular arrays of Rydberg atoms. We show that platforms made publicly available recently allow empirical explorations of the critical behavior of quantum simulators. We discuss recent progress regarding the phase diagram of two-leg ladders, effective Hamiltonian approaches and the construction of hybrid quantum algorithms targeting hadronization in collider physics event generators.

EW Higgs plus multi-jet event samples at parton level in HDF5 event format \(\sqrt{s}=14\,{\rm TeV}\) \(m_H=125\,{\rm GeV}\) \(\mu_R=\mu_F=\frac{1}{2}\Big(m_{\perp,H}+\sum_{jets}p_{\perp,j}\Big)\) Generated with Sherpa using the attached setup files

VBF Higgs plus multi-jet event samples at parton level in HDF5 event format \(\sqrt{s}=14\,{\rm TeV}\) \(m_H=125\,{\rm GeV}\) \(\mu_R=\mu_F=\frac{1}{2}\Big(m_{\perp,H}+\sum_{jets}p_{\perp,j}\Big)\) Generated with Sherpa using the attached setup files