Alan Barr

We present the kinematic variable,mT2, which is in some ways similar to the more familiar 'transverse mass', but which can be used in events where two or more particles have escaped detection. We define this variable and describe the event topologies to which it applies, then present some of its mathematical properties. We then briefly discuss two case studies which show how mT2 is vital when reconstructing the masses of supersymmetric particles in mSUGRA-like and AMSB-like scenarios at the large hadron collider.

Abstract High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF’s physics potential.

A rather general method for determining the spin density matrix of a multi-particle system from angular decay data is presented. The method is based on a Bloch parameterisation of the $d$-dimensional generalised Gell-Mann representation of $\rho$ and exploits the associated Wigner- and Weyl-transforms on the sphere. Each parameter of a (possibly multipartite) spin density matrix can be measured from a simple average over an appropriate set of experimental angular decay distributions. The general procedures for both projective and non-projective decays are described, and the Wigner $P$ and $Q$ symbols calculated for the cases of spin-half, spin-one, and spin-3/2 systems. The methods are used to examine Monte Carlo simulations of $pp$ collisions for bipartite systems: $pp\rightarrow W^+W^-$, $pp\rightarrow ZZ$, $pp\rightarrow ZW^+$, $pp\rightarrow W^+\bar{t}$, $t\bar{t}$, and those from the Higgs boson decays $H\rightarrow WW^{*}$ and $H\rightarrow ZZ^*$. Measurements are proposed for entanglement detection, exchange symmetry detection and Bell inequality violation in bipartite systems.

We consider the application of endpoint techniques to the problem of mass determination for new particles produced at a hadron collider, where these particles decay to an invisible particle of unknown mass and one or more visible particles of known mass. We also consider decays of these types for pair-produced particles and in each case consider situations both with and without initial state radiation. We prove that, in most (but not all) cases, the endpoint of an appropriate transverse mass observable, considered as a function of the unknown mass of the invisible particle, has a kink at the true value of the invisible particle mass. The co-ordinates of the kink yield the masses of the decaying particle and the invisible particle. We discuss the prospects for implementing this method at the LHC.

Higgs boson self-interactions can be investigated via di-Higgs (pp→hh+X) production at the LHC. With a small O(30)fb Standard Model production cross section, and a large tt¯ background, this measurement has been considered challenging, even at a luminosity-upgraded LHC. We demonstrate that by using simple kinematic bounding variables, of the sort already employed in existing LHC searches, the dominant tt¯ background can be largely eliminated. Simulations of the signal and the dominant background demonstrate the prospect for measurement of the di-Higgs production cross section at the 30% level using 3ab−1 of integrated luminosity at a high luminosity LHC. This corresponds to a Higgs self-coupling determination with 60% accuracy in the bb¯τ+τ− mode, with potential for further improvements from e.g. subjet technologies and from additional di-Higgs decay channels.

Higgs boson decays produce pairs of $W$ bosons in a maximally entangled state, the spins of which can be expected to violate Bell inequalities. We show that the spin density matrix of the $W^\pm$ pair may be reconstructed experimentally from the directions of the charged lepton decay products, and from it the expectation values of various Bell operators determined. Numerical simulations of $H\rightarrow WW^*$ decays indicate that violation of a generalised CHSH inequality is unlikely to be measurable, however the CGLMP inequality is near-maximally violated. Experimental Bell tests could be performed at a variety of colliders and in different production channels. If reconstruction effects and backgrounds can be controlled then statistically significant violations could be observable even with datasets comparable to those already collected at the LHC.

If signals suggesting supersymmetry (SUSY) are discovered at the LHC then it will be vital to measure the spins of the new particles to demonstrate that they are indeed the predicted super-partners. A method is discussed by which the spins of some of the SUSY particles can be determined. Angular distributions in sparticle decays lead to charge asymmetry in lepton-jet invariant mass distributions. The size of the asymmetry is proportional to the primary production asymmetry between squarks and anti-squarks. Monte Carlo simulations are performed for a particular mSUGRA model point at the LHC. The resultant asymmetry distributions are consistent with a spin-0 slepton and a spin-12χ˜20, but are not consistent with both particles being scalars.

The ABCD3TA is a 128-channel ASIC with binary architecture for the readout of silicon strip particle detectors in the Semiconductor Tracker of the ATLAS experiment at the Large Hadron Collider (LHC). The chip comprises fast front-end and amplitude discriminator circuits using bipolar devices, a binary pipeline for first level trigger latency, a second level derandomising buffer and data compression circuitry based on CMOS devices. It has been designed and fabricated in a BiCMOS radiation resistant process. Extensive testing of the ABCD3TA chips assembled into detector modules show that the design meets the specifications and maintains the required performance after irradiation up to a total ionising dose of 10 Mrad and a 1-MeV neutron equivalent fluence of 2×1014 n/cm2, corresponding to 10 years of operation of the LHC at its design luminosity. Wafer screening and quality assurance procedures have been developed and implemented in large volume production to ensure that the chips assembled into modules meet the rigorous acceptance criteria.

This paper describes the silicon microstrip modules in the barrel section of the SemiConductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The module requirements, components and assembly techniques are given, as well as first results of the module performance on the fully assembled barrels that make up the detector being installed in the ATLAS experiment.

A new method is presented for measuring the spin of selectrons and smuons at the Large Hadron Collider (LHC), using an angular variable which is sensitive to the polar angle in direct slepton pair production. This variable is invariant under boosts along the beam axis, so it can be used at the LHC despite the fact that the longitudinal boost of the centre-of-mass frame cannot be determined. Monte Carlo simulations demonstrate that, using this method, the LHC can distinguish between the supersymmetric production angular distribution and phase space, or between supersymmetry and the production angular distribution of universal extra dimensions. An integrated luminosity of about 100 to 300 inverse fb provides sufficient statistics to measure the slepton spin for points which had left-handed slepton masses in the range 202 to 338 GeV, and right-handed sleptons in the range 143 to 252 GeV. Good sensitivity was found in the `bulk' and `stau co-annihilation' regions of the cMSSM favoured by cosmological relic density measurements. Various systematic uncertainties are investigated, and some methods for reducing them are discussed.

We re-examine the kinematic variable mT2 and its relatives in the light of recent work by Cheng and Han. Their proof that mT2 admits an equivalent, but implicit, definition as the `boundary of the region of parent and daughter masses that is kinematically consistent with the event hypothesis' is far-reaching in its consequences. We generalize their result both to simpler cases (mT, the transverse mass) and to more complex cases (mTGen). We further note that it is possible to re-cast many existing and unpleasant proofs (e.g. those relating to the existence or properties of ``kink'' and ``crease'' structures in mT2) into almost trivial forms by using the alternative definition. Not only does this allow us to gain better understanding of those existing results, but it also allows us to write down new (and more or less explicit) definitions of (a) the variable that naturally generalizes mT2 to the case in which the parent or daughter particles are not identical, and (b) the inverses of mT and mT2 — which may be useful if daughter masses are known and bounds on parent masses are required. We note the implications that these results may have for future matrix-element likelihood techniques.

We review the methods which have been proposed for measuring masses of new particles at the Large Hadron Collider paying particular attention to the kinematical techniques suitable for extracting mass information when invisible particles are expected.

An important physics goal of a possible next-generation high-energy hadron collider will be precision characterisation of the Higgs sector and electroweak symmetry breaking. A crucial part of understanding the nature of electroweak symmetry breaking is measuring the Higgs self-interactions. We study dihiggs production in proton-proton collisions at 100 TeV centre of mass energy in order to estimate the sensitivity such a machine would have to variations in the trilinear Higgs coupling around the Standard Model expectation. We focus on the $$ b\overline{b}\gamma \gamma $$ final state, including possible enhancements in sensitivity by exploiting dihiggs recoils against a hard jet. We find that it should be possible to measure the trilinear self-coupling with 40% accuracy given 3/ab and 12% with 30/ab of data.

We perform a detailed analysis of the possible violation of various Bell-type inequalities for systems of vector boson-antiboson pairs. Considering the general case of an overall scalar state of the bipartite system, we identify two distinct classes of such states, and determine the joint probabilities of spin measurement outcomes for each them. We calculate the expectation values of the CHSH, Mermin and CGLMP inequalities and find that while the generalised CHSH inequality is not expected to be violated for any of the scalar states, in the case of the Mermin and CGLMP inequalities the situation is different -- these inequalities can be violated in certain scalar states while they cannot be violated in others. Moreover, the degree of violation depends on the relative speed of the two particles.

This paper describes the AC-coupled, single-sided, p-in-n silicon microstrip sensors used in the Semiconductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The sensor requirements, specifications and designs are discussed, together with the qualification and quality assurance procedures adopted for their production. The measured sensor performance is presented, both initially and after irradiation to the fluence anticipated after 10 years of LHC operation. The sensors are now successfully assembled within the detecting modules of the SCT, and the SCT tracker is completed and integrated within the ATLAS Inner Detector. Hamamatsu Photonics Ltd. supplied 92.2% of the 15,392 installed sensors, with the remainder supplied by CiS.

We introduce a new kinematic event variable mTGen which can provide information relating to the mass scales of particles pair-produced at hadronic and leptonic colliders. The variable is of particular use in events with a large number of particles in the final state when some of those particles are massive and not detected, such as may arise in R-parity-conserving supersymmetry.

This paper seeks to demonstrate that many of the existing mass-measurement variables proposed for hadron colliders (mT, mEff, mT2, missing pT, hT, rootsHatMin, etc.) are far more closely related to each other than is widely appreciated, and indeed can all be viewed as a common mass bound specialized for a variety of purposes. A consequence of this is that one may understand better the strengths and weaknesses of each variable, and the circumstances in which each can be used to best effect. In order to achieve this, we find it necessary first to revisit the seemingly empty and infertile wilderness populated by the subscript "T" (as in pT) in order to remind ourselves what this process of transversification actually means. We note that, far from being simple, transversification can mean quite different things to different people. Those readers who manage to battle through the barrage of transverse notation distinguishing mass-preserving projections from velocity preserving projections, and `early projection' from `late projection', will find their efforts rewarded towards the end of the paper with (i) a better understanding of how collider mass variables fit together, (ii) an appreciation of how these variables could be generalized to search for things more complicated than supersymmetry, (iii) will depart with an aversion to thoughtless or naive use of the so-called `transverse' methods of any of the popular computer Lorentz-vector libraries, and (iv) will take care in their subsequent papers to be explicit about which of the 61 identified variants of the `transverse mass' they are employing.

The discovery potential of the LHC is investigated for the minimal anomaly-mediated supersymmetry breaking (mAMSB) scenario, using the ATLAS fast detector simulator, including track reconstruction and particle identification. Generic supersymmetry search cuts are used to map the 5 σ (and ⩾ 10 event) discovery contours in the m0–m3/2 plane. With 100 fb−1 of integrated luminosity the search will reach up to 2.8 TeV in the squark mass and 2.1 TeV in the gluino mass. We generalise a kinematical variable and demonstrate that it is sensitive to the small chargino-LSP mass splitting characteristic of AMSB models. By identifying tracks from chargino decays we show that the Wino-like nature of the LSP can be determined for a wide range of chargino lifetimes.

It is expected that hadron collider measurements of the Higgs boson mass using the decay h -> W^+W^-, followed by the leptonic decay of each W-boson, will be performed by fitting the shape of a distribution which is sensitive to the Higgs mass. We demonstrate that the variable most commonly used to measure the Higgs mass in this channel is not optimal as it contains an unnecessary and even counter-productive approximation. We remove that approximation, without introducing any cost in complexity, and demonstrate that the new variable is a clear improvement over the old: its performance is never worse, and in some cases (particularly the high Higgs mass region) it might reduce the fit uncertainty on the Higgs mass in that channel by a factor approaching two.

The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation.

We develop techniques to determine the mass scale of invisible particles pair-produced at hadron colliders. We employ the constrained mass variable ${m}_{2C}$, which provides an event-by-event lower bound to the mass scale given a mass difference. We complement this variable with a new variable ${m}_{2C,UB}$ which provides an additional upper bound to the mass scale and demonstrate its utility with a realistic case study of a supersymmetry model. These variables together effectively quantify the ``kink'' in the function $\mathtt{m}\mathtt{a}\mathtt{x}$ ${m}_{T2}$ which has been proposed as a mass-determination technique for collider-produced dark matter. An important advantage of the ${m}_{2C}$ method is that it does not rely simply on the position at the end point, but it uses the additional information contained in events which lie far from the end point. We found the mass by comparing the $\mathtt{H}\mathtt{E}\mathtt{R}\mathtt{W}\mathtt{I}\mathtt{G}$ generated ${m}_{2C}$ distribution to ideal distributions for different masses. We find that for the case studied, with $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity (about 400 signal events), the invisible particle's mass can be measured to a precision of 4.1 GeV. We conclude that this technique's precision and accuracy is as good as, if not better than, the best known techniques for invisible-particle mass determination at hadron colliders.

The design and technology of the silicon strip detector modules for the Semiconductor Tracker (SCT) of the ATLAS experiment have been finalised in the last several years. Integral to this process has been the measurement and verification of the tracking performance of the different module types in test beams at the CERN SPS and the KEK PS. Tests have been performed to explore the module performance under various operating conditions including detector bias voltage, magnetic field, incidence angle, and state of irradiation up to 3×1014 protons per square centimetre. A particular emphasis has been the understanding of the operational consequences of the binary readout scheme.

Optical links are used for the readout of the 4088 silicon microstrip modules that make up the SemiConductor Tracker of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The optical link requirements are reviewed, with particular emphasis on the very demanding environment at the LHC. The on-detector components have to operate in high radiation levels for 10 years, with no maintenance, and there are very strict requirements on power consumption, material and space. A novel concept for the packaging of the on-detector optoelectronics has been developed to meet these requirements. The system architecture, including its redundancy features, is explained and the critical on-detector components are described. The results of the extensive Quality Assurance performed during all steps of the assembly are discussed.

We describe how one may employ a very simple event selection, using only the kinematic variable mT2, to search for new particles at the LHC. The method is useful when searching for evidence of models (such as R-parity conserving supersymmetry) which have a Z2 parity and a weakly-interacting lightest parity-odd particle. We discuss the kinematic properties which make this variable an excellent discriminant against the great majority of Standard Model backgrounds. Monte Carlo simulations suggest that this approach could be used to discover supersymmetry with somewhat smaller integrated luminosities (or perhaps lower center-of-mass energies) than would be required for other comparable analyses.

We further develop the constrained mass variable techniques to determine the mass scale of invisible particles pair-produced at hadron colliders. We introduce the constrained mass variable ${M}_{3C}$ which provides an event-by-event lower bound and upper bound to the mass scale given the two mass differences between the lightest three new particle states. This variable is most appropriate for short symmetric cascade decays involving two-body decays and on-shell intermediate states which end in standard-model particles and two dark-matter particles. An important feature of the constrained mass variables is that they do not rely simply on the position of the end point but use the additional information contained in events which lie far from the end point. To demonstrate our method we study the supersymmetric model SPS 1a. We select cuts to study events with two ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{2}^{o}$ each of which decays to ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{o}$, and two opposite-sign same-flavor charged leptons through an intermediate on-shell slepton. We find that with $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity the invisible-particle mass can be measured to ${M}_{{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{o}}=96.4\ifmmode\pm\else\textpm\fi{}2.4\text{ }\text{ }\mathrm{GeV}$. Combining fits to the shape of the ${M}_{3C}$ constrained mass variable distribution with the $\mathrm{max}{m}_{ll}$ edge fixes the mass differences to $\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{GeV}$.

Current Large Hadron Collider (LHC) analyses are blind to compressed supersymmetry (SUSY) models with sleptons near the lightest super partner (LSP) in mass: $$ {m}_{\tilde{l}}-{m}_{{\tilde{\chi}}_1^0} $$ ≡ Δm ≲ 60 GeV. We present a search sensitive to the very compressed range 1 3 GeV < Δm < 24 GeV using the channel $$ pp\to {\tilde{l}}^{+}{\tilde{l}}^{-} $$ + jet → $$ {l}^{+}{l}^{-}{\tilde{\chi}}_1^0{\tilde{\chi}}_1^0+ $$ jet with soft same-flavor leptons and one hard jet from initial state radiation (p T > 100 GeV). The sleptons recoil against the jet boosting them and their decay products, making the leptons detectable and providing substantial missing transverse momentum. We use the kinematic variable mT2 along with a different-flavor control region to reduce the large standard model backgrounds and control systematic uncertainty. We find the analysis should allow LHC14 with 100 fb−1 to search for degenerate left-handed selectrons and smuons in the compressed region up to $$ {m}_{{\tilde{l}}_L} $$ ≲ 150 GeV. In addition, it should be sensitive to $$ {m}_{{\tilde{l}}_L} $$ ≲ 110 GeV for the very challenging case of auto-concealed SUSY, in which left-handed sleptons decay to the Kaluza-Klein tower of a modulino LSP which lives in d = 6 extra dimensions. In both the compressed spectrum and auto-concealed SUSY scenarios this analysis will need more data to improve on LEP2 limits for right-handed sleptons due to their smaller cross sections.

FASER-2 is a potential upgrade to the FASER experiment, and could be hosted in the proposed Forward Physics Facility (FPF) 620m to the west of the ATLAS interaction point, in the far-forward region of the LHC collisions. The experiment would have sensitivity for long-lived particles (LLPs) produced by rare meson decays that could be potential candidates for light dark matter. The proposed upgrade involves a significantly enlarged volume compared to FASER, resulting in an increase in reach for various BSM signals of several orders of magnitude and allows sensitivity to models that were previously out of reach, such as Dark Higgs and Heavy Neutral Leptons. This poster will present the development of a tracking software for the FASER-2 experiment using the A Common Tracking Software (ACTS) toolkit to aid in accurate mass and pointing reconstruction of charged particles. The developed tracking software will be used to compare various FASER-2 layouts and tracker technologies, thereby contributing to the design studies of the FASER-2 experiment.

The study of entanglement in particle physics has been gathering pace in the past few years. It is a new field that is providing important results about the possibility of detecting entanglement and testing Bell inequality at colliders for final states as diverse as top-quark or $\tau$-lepton pairs, massive gauge bosons and vector mesons. In this review, after presenting definitions, tools and basic results that are necessary for understanding these developments, we summarize the main findings -- as published up to the end of year 2023. These investigations have been mostly theoretical since the experiments are only now catching up, with the notable exception of the observation of entanglement in top-quark pair production at the Large Hadron Collider. We include a detailed discussion of the results for both qubit and qutrits systems, that is, final states containing spin one-half and spin one particles. Entanglement has also been proposed as a new tool to constrain new particles and fields beyond the Standard Model and we introduce the reader to this promising feature as well.

Different search strategies for supersymmetry have been employed by the LHC general-purpose experiments using early data. As proven by their early results, these strategies are promising, but raise the question of how well they will generalize for the future. We address this question by studying two thousand phenomenological minimal supersymmetric standard model parameter space points that come from a fit to indirect and cosmological data. We examine the 5 sigma discoverability of the points employing a typical ATLAS-type search based on missing transverse momentum (MET), a search based on an optimised MT2 cut and a combination of the two, taking into account standard model backgrounds. The discovery reach of the strategies can depend strongly on the systematic uncertainty in the background, subject to the stringency of the cuts and the details of the background simulation. By combining the MET and MT2 based strategies, with an integrated luminosity of 1 fb^-1 (10 fb^-1) at 7 TeV, 4-8% (42%) of the points are discoverable, depending on the systematic uncertainty on the background. At 14 TeV and with 10 fb^-1, 96% of the points are discoverable. While the majority of points can be discovered by both strategies at sqrt{s} = 14 TeV and with 1 fb^-1, there are some that are left undiscovered by a MET search strategy, but which are discovered by the MT2 strategy, and vice versa, therefore it is essential that one performs both in parallel. We discuss some of the factors that can make points more difficult to observe.

The SemiConductor Tracker (SCT) data acquisition (DAQ) system will calibrate, configure, and control the approximately six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests

The ATLAS SemiConductor Tracker (SCT) was built in three sections: a barrel and two end-caps. This paper describes the design, construction and final integration of the barrel section. The barrel is constructed around four nested cylinders that provide a stable and accurate support structure for the 2112 silicon modules and their associated services. The emphasis of this paper is directed at the aspects of engineering design that turned a concept into a fully-functioning detector, as well as the integration and testing of large sub-sections of the final SCT barrel detector. The paper follows the chronology of the construction. The main steps of the assembly are described with the results of intermediate tests. The barrel service components were developed and fabricated in parallel so that a flow of detector modules, cooling loops, opto-harnesses and Frequency-Scanning-Interferometry (FSI) alignment structures could be assembled onto the four cylinders. Once finished, each cylinder was conveyed to the next site for the mounting of modules to form a complete single barrel. Extensive electrical and thermal function tests were carried out on the completed single barrels. In the next stage, the four single barrels and thermal enclosures were combined into the complete SCT barrel detector so that it could be integrated with the Transition Radiation Tracker (TRT) barrel to form the central part of the ATLAS inner detector. Finally, the completed SCT barrel was tested together with the TRT barrel in noise tests and using cosmic rays.

Basic multivalued building blocks constructed using CCD (charge-coupled devices) technology are presented. They are used to realize simple threshold functions. Existing techniques for decomposition of multivalued multithreshold functions into simpler subfunctions are reviewed. Usage of the CCD technology in implementation of these subfunctions is discussed. Two new decomposition techniques are proposed. Their aim is to obtain realizations that are better suited to CCD technology in terms of the maximum number of thresholds per element and the generation of negative weights. Synthesis techniques based on the proposed decompositions are presented and compared. Although 4-valued logic functions are stressed, the techniques are, in principle, applicable to functions of any radix.

In 2004 at the ATLAS (A Toroidal LHC ApparatuS) combined test beam, one slice of the ATLAS barrel detector (including an Inner Detector set-up and the Liquid Argon calorimeter) was exposed to particles from the H8 SPS beam line at CERN. It was the first occasion to test the combined electron performance of ATLAS. This paper presents results obtained for the momentum measurement p with the Inner Detector and for the performance of the electron measurement with the LAr calorimeter (energy E linearity and resolution) in the presence of a magnetic field in the Inner Detector for momenta ranging from 20 GeV/c to 100 GeV/c. Furthermore the particle identification capabilities of the Transition Radiation Tracker, Bremsstrahlungs-recovery algorithms relying on the LAr calorimeter and results obtained for the E/p ratio and a way how to extract scale parameters will be discussed.

Discovery of the Higgs boson in any decay channel depends on the existence of event variables or cuts with sensitivity to the presence of the Higgs. We demonstrate the non-optimality of the kinematic variables which are currently expected to play the largest role in the discovery (or exclusion) of the Higgs at the LHC in the ττ channel. Any LHC collaboration looking for opportunities to gain advantages over its rivals should, perhaps, consider the alternative strategy we propose.

The measurement of sparticle masses in the Minimal Supersymmetric Standard Model at the LHC is analysed, in the scenario where the lightest neutralino, the 01, decays into three quarks. Such decays, occurring through the baryon-number violating coupling λ''ijk, pose a severe challenge to the capability of the LHC detectors since the final state has no missing energy signature and a high jet multiplicity. We focus on the case λ''212≠0 which is the most difficult experimentally. The proposed method is valid over a wide range of SUGRA parameter space with λ''212 ∼ 10−5−0.1. Simulations are performed of the ATLAS detector at the Large Hadron Collider. Using the 01 from the decay chain L→02q→Rℓq→01ℓℓq, we show that the 01 and 02 masses can be measured by 3-jet and 3-jet + lepton pair invariant mass combinations. At the SUGRA pointm0 = 100 GeV, m1/2 = 300 GeV,A0 = 300 GeV, tan β = 10, μ > 0 and with λ''212 = 0.005, we achieve statistical (systematic) errors of 3 (3), 3 (3), 0.3 (4) and 5 (12) GeV, respectively for the masses of the 01, 02, R and L, with an integrated luminosity of 30 fb−1.

This paper examines unexplored correlations in the parameter spaces probed by recent ATLAS analyses for gluinos and squarks, addressing various shortcomings in the literature. Six 13 TeV ATLAS analyses based on 3.2 fb $$^{-1}$$ of integrated luminosity are interpreted in the 19-parameter R-parity conserving phenomenological minimal supersymmetric extension to the Standard Model (pMSSM). The distinct regions covered by each search are independent of prior, and we reveal particularly striking complementarity between the 2–6 jets and Multi-b searches. In the leptonic searches, we identify better sensitivity to models than those used for analysis optimisation, notably a squark–slepton–wino scenario for the SS/3L search. Further, we show how collider searches for coloured states probe the structure of the pMSSM dark sector more extensively than the Monojet analysis alone, with sensitivity to parameter spaces that are challenging for direct detection experiments.

If signals suggesting supersymmetry (SUSY) are discovered at the LHC then it will be vital to measure the spin of the new particles to demonstrate that they are indeed the predicted super-partners. A method is discussed by which the spins of some of the SUSY particles can be investigated. Angular distributions in sparticle decays lead to charge asymmetry in lepton-jet invariant mass distributions. The size of the asymmetry is proportional to the primary production asymmetry between squarks and anti-squarks. Monte Carlo simulations are performed for a particular mSUGRA model point at the LHC. The resultant asymmetry distributions are consistent with a spin-0 slepton and a spin-half neutralino-two, but are not consistent with the pure phase-space decays one would obtain from both sparticles being scalars.

We present the kinematic variable, m_T2, which is in some ways similar to the more familiar `transverse-mass', but which can be used in events where two or more particles have escaped detection. We define this variable and describe the event topologies to which it applies, then present some of its mathematical properties. We then briefly discuss two case studies which show how m_T2 is vital when reconstructing the masses of supersymmetric particles in mSUGRA-like and AMSB-like scenarios at the Large Hadron Collider.

This collection of studies on new physics at the LHC constitutes the report of the supersymmetry working group at the Workshop `Physics at TeV Colliders', Les Houches, France, 2007. They cover the wide spectrum of phenomenology in the LHC era, from alternative models and signatures to the extraction of relevant observables, the study of the MSSM parameter space and finally to the interplay of LHC observations with additional data expected on a similar time scale. The special feature of this collection is that while not each of the studies is explicitely performed together by theoretical and experimental LHC physicists, all of them were inspired by and discussed in this particular environment.

We present a comment on the kinematic variable ${m}_{CT2}$ recently proposed in Won Sang Cho, Jihn E. Kim, and Ji-Hun Kim, Phys. Rev. D 81, 095010 (2010). The variable is designed to be applied to models such as $R$-parity conserving supersymmetry (SUSY) when there is pair production of new heavy particles each of which decays to a single massless visible and a massive invisible component. It was proposed by Cho, Kim, and Kim that a measurement of the peak of the ${m}_{CT2}$ distribution could be used to precisely constrain the masses of the SUSY particles. We show that, for the an example characterized by direct squark decays, when standard model backgrounds are included in simulations, the sensitivity of the ${m}_{CT2}$ variable to the SUSY particle masses is more seriously impacted for ${m}_{CT2}$ than for other previously proposed variables.

We reconsider observables for discovering and measuring the mass of a Higgs boson via its di-leptonic decays: H --> WW* --> l nu l nu. We define an observable generalizing the transverse mass that takes into account the fact that one of the intermediate W-bosons is likely to be on-shell. We compare this new variable with existing ones and argue that it gives a significant improvement for discovery in the region m_h < 2 m_W.

We describe the construction, test and installation procedures, and the experience gained with the operation of a small but complete system of high-rate Micro-Strip Gas Chambers, made on thin borosilicate glass with a diamond-like coating with chromium or gold strips. A set of detectors, fully equipped with read-out electronics and each with an active area of 100 × 100 mm2, was exposed during six months to a high-intensity muon beam at CERN with a peak intensity of ∼ 104 mm−2s−1. Continuous monitoring of the performance of the chambers during the beam runs allowed the evaluation of detection efficiency and the monitoring of accidental rates, as well as the study of ambient induced variations and aging in realistic beam conditions. No significant difference has been found in the operation of under-and over-coated plates. Efficiencies could reach ∼ 98% in best operating conditions, although local lower values were often observed due to missing channels (open strips, broken bonds and dead electronic channels). The long-term operation of the chambers has been more difficult than expected, with the appearance of break-downs and loss of efficiency in some detectors, possibly induced by the presence of small gas leaks, to water permeation or to residual reactivity of the quencher gas (dimethylether).

The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented – these will be of interest to other builders of large-scale tracking detectors. The SCT end-caps will be fully connected at the start of 2008. Further commissioning will continue, to be ready for proton-proton collision data in 2008.

The detection of the flavour content of jets produced from R-parity violating neutralino decays is investigated in the case where one baryon-number violating coupling dominates. Simulations are performed of the ATLAS experiment at the LHC for all couplings, other than lambda"_tjk since neutralino decays through these couplings are very suppressed. Secondary vertex distributions and muons produced by heavy-quark (b- and c-) jets allow discrimination between LSP decay modes. The dominant coupling can be identified at better than 3.5 sigma in almost all cases, with the only remaining ambiguity caused by the inability to distinguish strange from down quarks.

A small set of final prototypes of the ATLAS Inner Detector silicon tracking system (Pixel Detector and SemiConductor Tracker), were used to take data during the 2004 Combined Test Beam. Data were collected from runs with beams of different flavour (electrons, pions, muons and photons) with a momentum range of 2 to 180 GeV/c. Four independent methods were used to align the silicon modules. The corrections obtained were validated using the known momenta of the beam particles and were shown to yield consistent results among the different alignment approaches. From the residual distributions, it is concluded that the precision attained in the alignment of the silicon modules is of the order of 5 μm in their most precise coordinate.

We reconsider observables for discovering a heavy Higgs boson (with mh>2mW) via its dileptonic decays h→WW→ℓνℓν. We show that observables generalizing the transverse mass that take into account the fact that both of the intermediate W-bosons are likely to be on-shell give a significant improvement over the variables used in existing searches. We also comment on the application of these observables to other decays which proceed via narrow-width intermediates.

The engagement of Citizen Scientists with the HiggsHunters.org citizen science project is investigated through analysis of behaviour, discussion, and survey data. More than 37,000 Citizen Scientists from 179 countries participated, classifying 1,500,000 features of interest on about 39,000 distinct images. While most Citizen Scientists classified only a handful of images, some classified hundreds or even thousands. Analysis of frequently-used terms on the dedicated discussion forum demonstrated that a high level of scientific engagement was not uncommon. Evidence was found for a emergent and distinct technical vocabulary developing within the Citizen Science community. A survey indicates a high level of engagement and an appetite for further LHC-related citizen science projects.

The combined constraints from six early Run 2 ATLAS searches for supersymmetry are interpreted in the phenomenological minimal supersymmetric extension to the Standard Model (pMSSM). Each of the searches was based on proton-proton collision data recorded in 2015 at $\sqrt{s} =13$ TeV with 3.2 fb$^{-1}$ of integrated luminosity. Sensitivity to squarks of the first two generations and gluinos are evaluated using fast detector simulation. Results are presented in the 19-parameter R-parity conserving pMSSM with the lightest supersymmetric particle (LSP) being the neutralino. Considering 181.8k points that survived Run 1 constraints, 15.7% are excluded at 95% confidence level. Of those satisfying these Run 2 constraints, 0.5% (1.0%) have sub-TeV gluinos (sub-500 GeV squarks), the lightest of which has a mass of 757 GeV (293 GeV) with a 689 GeV (217 GeV) LSP.

The semiconductor tracker (SCT) will form a vital part of the ATLAS experiment, one of two general-purpose experiments for the forthcoming Large Hadron Collider (LHC) at the CERN laboratory. The active elements of the SCT are 4088 radiation-hard silicon detector modules, tiled on four barrel cylinders and eighteen end-cap disks. It will have in total more than 6 million channels each providing 1-bit binary signal discrimination every 25 nanoseconds. The SCT is currently in full production with macro-assembly taking place at several sites. During assembly, frequent quality assurance and characterization measurements are performed using the high-performance optoelectronic data acquisition system designed for the final experiment. This talk offers an overview of the data acquisition hardware, and the calibration and control systems for the electronics front-end, as well as early results from the macroconstruction.

The ATLAS SemiConductor Tracker (SCT) is one of the largest existing semiconductor detectors. It is situated between the Pixel detector and the Transition Radiation Tracker at one of the four interaction points of the Large Hadron Collider (LHC). During 2006-2007 the detector was lowered into the ATLAS cavern and installed in its final position. For the assembly, integration and commissioning phase, a complete Detector Control System (DCS) was developed to ensure the safe operation of the tracker. This included control of the individual powering of the silicon modules, a bi-phase cooling system and various types of sensors monitoring the SCT environment and the surrounding test enclosure. The DCS software architecture, performance and operational experience will be presented in the view of a validation of the DCS for the final SCT installation and operation phase.

The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same simulation and reconstruction tools as those used for the ATLAS detector itself.

Received 2 February 2012DOI:https://doi.org/10.1103/PhysRevLett.108.109902© 2012 American Physical Society

(1975). Optimum Zero-Memory Strategy and Exact Probabilities for 4-Deck Blackjack. The American Statistician: Vol. 29, No. 2, pp. 84-88.

Prepared for the Environmental Protection AgencybyCentre for the Environment, Trinity College, DublinAuthors:Eleanor Jennings, Paul Mills, Philip Jordan, Jens-Peder Jensen,Martin Sondergaard, Alan Barr, Grace Glasgow and Kenneth IrvineENVIRONMENTAL PROTECTION AGENCYAn Ghniomhaireacht um Chaomhnu ComhshaoilPO Box 3000, Johnstown Castle, Co. Wexford, IrelandTelephone: +353-53-60600 Fax: +353-53-60699E-mail: info@epa.ie Website: www.epa.ie

Journal of Marriage and FamilyVolume 85, Issue 1 p. 1-5 Issue InformationFree Access Issue Information First published: 05 January 2023 https://doi.org/10.1111/jomf.12855AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Volume85, Issue1February 2023Pages 1-5 RelatedInformation

Recent instances of successful application of quantum information techniques to particle physics problems invite for an analysis of the mathematical details behind such connection. In this paper, we identify the Choi-Jamiolkowski isomorphism, or state-channel duality, as a theoretical principle enabling the application of the theory of quantum information to the scattering amplitudes associated with Standard Model processes.

We revisit the process of transversification and agglomeration of particle momenta that are often performed in analyses at hadron colliders, and show that many of the existing mass-measurement variables proposed for hadron colliders are far more closely related to each other than is widely appreciated, and indeed can all be viewed as a common mass bound specialized for a variety of purposes.

Using data from the this http URL project we investigate the ability of non-expert citizen scientists to identify long-lived particles, and other unusual features, in images of LHC collisions recorded by the ATLAS experiment. More than 32,000 volunteers from 179 countries participated, classifying 1,200,000 features of interest on about 39,000 distinct images. We find that the non-expert volunteers are capable of identifying the decays of long-lived particles with an efficiency and fake-rate comparable to that of the ATLAS algorithms. Volunteers also picked out events with unexpected features, including what appeared to be an event containing a jet of muons.

Abstract. This study assesses a filtering procedure on accumulating precipitation gauge measurements, and quantifies the effects of bias corrections for wind-induced undercatch across four ecoclimatic regions in western Canada, including the permafrost regions of the Sub-arctic, the Western Cordillera, the Boreal Forest, and the Prairies. The bias corrections increased monthly precipitation by up to 163 % at windy sites with short vegetation, and sometimes modified the seasonal precipitation regime, whereas the increases were less than 13 % at sites shielded by forest. On a yearly basis, the increase of total precipitation ranged from 8 to 20 mm (3–4 %) at sites shielded by vegetation, and 60 to 384 mm (about 15–34 %) at open sites. In addition, the bias corrections altered the seasonal precipitation patterns at some windy sites with high snow percentage (&gt; 50 %). This study highlights the need and importance of precipitation bias corrections at both research sites and operational networks for water balance assessment and the validation of global/regional climate/hydrology models.

We describe recent measurements carried out in well controlled and reproducible conditions to help understanding the factors affecting the short- and long-term behaviour of Microstrip Gas Chambers. Special care has been taken concerning the gas purity and choice of materials used in the system and for the detectors construction. Detectors built on glasses with surface resistivity in the range 1013–1015 Ω/□ have shown satisfactory performance as they do not show charging-up process at high rate and stand the large doses required for the future high luminosity experiments (∼10 mC-cm−1.yr−1). Concerning the lifetime measurements, it has been observed that chambers manufactured on high-resistivity glass are far more susceptible of suffering ageing than detectors made on low resistivity, electron-conducting supports, independently of the metal used for the artwork (chromium or gold) at least in clean gas conditions. The successfully operation in the laboratory of detectors manufactured on diamond-coated glass with a surface resistivity around 1015 Ω/□ confirms the last statement. Results from a long-term, high rate beam test are also reported.

Because different needs and priorities call for different approaches, the document does not present a single curriculum. Instead it provides a statement of the purpose, elements and competences for community engagement practice that should enable training providers to develop their own curricula to address the needs of practitioners operating in different settings. We hope that this approach can make a significant contribution to establishing a range of learning opportunities that will deliver the best practice needed to deliver on policy commitments and to put communities first.

This manual is designed to assist in the planning and evaluation of practice in a participatory manner. This is a detailed exploration of the LEAP model. Shorter introductory explanations are available in ' LEAP - step by step' and in the online learning tool. These may be particularly useful for those coming to LEAP for the first time.

Equine Veterinary EducationVolume 29, Issue 2 p. 57-57 Issue InformationFree Access Issue Information First published: 08 January 2017 https://doi.org/10.1111/eve.12661Citations: 1AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume29, Issue2February 2017Pages 57-57 RelatedInformation

We describe recent developments on diamond-like carbon (DLC) over-coated Microstrip Gas Chambers made on boro-silicate drawn glass substrates. MSGC surface coating with thin DLC layer of stable and controlled resistivity was proposed to overcome the limitation of detector operation due to surface charging-up under avalanches. This brings also advantages for the detector manufacturing technology. The thin layer, deposited on top of a manufactured MSGC (over-coating), demonstrates excellent mechanical properties and very good stability. We report on recent measurements with DLC over-coated MSGCs of various surface resistivities (ranging from 101Ω/□ to 1016 Ω/□ on D-263 and AF45 glass substrates. Over-coated MSGCs with resistivity of the surface around 1015Ω/□ exhibit a stable charge gain up to radiation rates in excess of 106 Hz/mm2. Stable long-term operation up to 50 mC/cm of accumulated charge from avalanches has been demonstrated.

This thesis demonstrates that supersymmetry can be discovered with the ATLAS experiment even if nature conspires to choose one of two rather difficult cases. In the first case where baryon-number is weakly violated, the lightest supersymmetric particle decays into three quarks. This leads to events with a very large multiplicity of jets which presents a difficult combinatorical problem at a hadronic collider. The distinctive property of the second class of model – anomaly-mediation – is the near degeneracy of the super-partners of the SU(2) weak bosons. The heavier charged wino decays producing its invisible neutral partner, the presence of which must be inferred from the apparent non-conservation of transverse momentum, as well as secondary particle(s) with low transverse momentum which must be extracted from a large background. Monte-Carlo simulations are employed to show that for the models examined not only can the distinctive signature of the model can be extracted, but that a variety of measurements (such as of sparticle masses) can also be made. The final two chapters present an investigation into part of the experimental hardware which will be vital for these analyses. Beam tests of ATLAS semiconductor tracker modules demonstrate that this sub-detector can be expected to perform to its specification, providing the good spatial resolution and efficiency with low noise, even after the equivalent of ten years of irradiation.

Equine Veterinary EducationVolume 31, Issue 10 p. 505-505 Issue InformationFree Access Issue Information First published: 05 September 2019 https://doi.org/10.1111/eve.12968AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume31, Issue10October 2019Pages 505-505 RelatedInformation

Rest of World), €218 (Europe), £187 (UK

Higgs boson decays produce pairs of W bosons in a maximally entangled state, the spins of which can be expected to violate Bell inequalities. We show that the spin density matrix of the $W^\pm$ pair may be reconstructed experimentally from the directions of the emitted leptons, and from it the expectation values of various Bell operators determined. Simulations of $H \rightarrow W^+W^-$ indicate that violation of the CHSH inequality is unlikely to be measurable, however the CGLMP inequality is near-maximally violated, with large statistical significances which might be observable even with existing LHC data.

We describe the assembly procedure and the operation in a high-intensity beam of a small but representative system of Micro Strip Gas Chambers (MSGC) fully equipped with readout electronics. The chambers, with an active area of 100 × 100 mm2, are made on 300 μm diamond-like coated D-263 glass with 200 μm pitch gold or chromium strips. The readout electronics (PreMux 128) allows the recording of charge on individual anode strips. The monitoring task includes a complete control and characterization of each device before installation in the beam, such as measurement of surface resistivity, finding shorts, pulse height analysis, gas gain calibration, rate capability and testing of the final electronics. Preliminary results of the beam test are described.

Equine Veterinary EducationVolume 28, Issue 10 p. 535-535 Issue InformationFree Access Issue Information First published: 09 September 2016 https://doi.org/10.1111/eve.12488AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume28, Issue10October 2016Pages 535-535 RelatedInformation

Equine Veterinary EducationVolume 28, Issue 8 p. 413-413 Issue InformationFree Access Issue Information First published: 08 July 2016 https://doi.org/10.1111/eve.12486AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume28, Issue8August 2016Pages 413-413 RelatedInformation

Equine Veterinary EducationVolume 28, Issue 4 p. 177-177 Issue InformationFree Access Issue Information First published: 02 March 2016 https://doi.org/10.1111/eve.12482AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume28, Issue4April 2016Pages 177-177 RelatedInformation

Using data from the HiggsHunters.org project we investigate the ability of non-expert citizen scientists to identify long-lived particles, and other unusual features, in images of LHC collisions recorded by the ATLAS experiment. More than 32,000 volunteers from 179 countries participated, classifying 1,200,000 features of interest on about 39,000 distinct images. We find that the non-expert volunteers are capable of identifying the decays of long-lived particles with an efficiency and fake-rate comparable to that of the ATLAS algorithms. Volunteers also picked out events with unexpected features, including what appeared to be an event containing a jet of muons.

The first search is reported for direct heffalon production, using 23.3/fb per experiment of delivered integrated luminosity of proton-proton collisions at rootS = 8TeV from the Large Hadron Collider. The data were recorded with the ATLAS and the CMS detectors. Each exotic composite is assumed to be stable on the detector lifetime (tau >> ns). A particularly striking signature is expected. No signal events are observed after event selection. The cross section for heffalon production is found to be less than 64ab at the 95% confidence level.

Attempting to find evidence for supersymmetry (SUSY) is one of the key aims of the ATLAS experiment at the Large Hadron Collider. This thesis is concerned with searching for supersymmetry in final states with 2-4 hadronic jets, missing transverse energy and no electrons or muons. In the first part, a search strategy is developed using 1.04 fb−1 of data from the first half of 2011. No excess over the Standard Model expectation is observed, so the data are used to set limits on two SUSY simplified models, in which pair-produced squarks or gluinos decay directly to neutralinos and jets. Good limits are achieved for scenarios where the neutralino is nearly as massive as the squark/gluino, compared to an earlier ATLAS analysis using the same dataset. For example, for pair-production of squarks decaying directly to neutralinos, all neutralino masses below 200 GeV are excluded at 95% confidence level when the squark mass is 300 GeV. Similarly, for pair-produced gluinos, neutralino masses below 300 GeV are excluded when the gluino mass is 400 GeV. The equivalent neutralino mass limits in the earlier analysis are 130 GeV and 240 GeV respectively. In the second part, the performance of the ATLAS missing transverse energy trigger is studied, and its suitability for use in the SUSY search is evaluated. The behaviour is found to be consistent with expectations, and the trigger strategy for 2010 data-taking is described.

The high energy of the Large Hadron Collider (LHC), together with the large integrated luminosity delivered to the general purpose experiments, oers unprecedented opportunities for searches for new particles beyond the Standard Model. Given the wealth of analyses and searches that have been reported, it is perhaps surprising that to date no search has been performed for some of the more exotic composites proposed in the literature. In this paper we concentrate on the search for the healon, for

A. J. Barr, T. J. Khoo, P. Konar, K. Kong, C. G. Lester, K. T. Matchev, and M. Park Department of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK Department of Physics, Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK Theoretical Physics Group, Physical Research Laboratory, Ahmedabad, Gujarat 380 009, India Department of Physics and Astronomy, University of Kansas, Lawrence, KA 66045, USA Department of Physics, University of Florida, Gainesville, FL 32611, USA (Dated: May 13, 2011)

A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.

The first search is reported for direct heffalon production, using 23.3/fb per experiment of delivered integrated luminosity of proton-proton collisions at rootS = 8TeV from the Large Hadron Collider. The data were recorded with the ATLAS and the CMS detectors. Each exotic composite is assumed to be stable on the detector lifetime (tau &gt;&gt; ns). A particularly striking signature is expected. No signal events are observed after event selection. The cross section for heffalon production is found to be less than 64ab at the 95% confidence level.