P. Gunnellini

We modify the treatment of multiple parton interactions (MPI) in Pythia by including the $$1\otimes 2\;$$ mechanism and treating the $$2 \otimes 2\;$$ mechanism in a model-independent way. The $$2 \otimes 2\;$$ mechanism is calculated within the mean field approximation, and its parameters are expressed through generalized parton distributions extracted from HERA data. The parameters related to the transverse parton distribution inside the proton are thus independent of the performed fit. The $$1\otimes 2\;$$ mechanism is included along the lines of the recently developed formalism in perturbative QCD. A unified description of MPI at moderate and hard transverse momenta is obtained within a consistent framework, in good agreement with experimental data measured at 7 TeV. Predictions are also shown for the considered observables at 14 TeV. The corresponding code implementing the new MPI approach is made available.

The successful operation of the Large Hadron Collider (LHC) and the excellent performance of the ATLAS, CMS, LHCb and ALICE detectors in Run-1 and Run-2 with $pp$ collisions at center-of-mass energies of 7, 8 and 13 TeV as well as the giant leap in precision calculations and modeling of fundamental interactions at hadron colliders have allowed an extraordinary breadth of physics studies including precision measurements of a variety physics processes. The LHC results have so far confirmed the validity of the Standard Model of particle physics up to unprecedented energy scales and with great precision in the sectors of strong and electroweak interactions as well as flavour physics, for instance in top quark physics. The upgrade of the LHC to a High Luminosity phase (HL-LHC) at 14 TeV center-of-mass energy with 3 ab$^{-1}$ of integrated luminosity will probe the Standard Model with even greater precision and will extend the sensitivity to possible anomalies in the Standard Model, thanks to a ten-fold larger data set, upgraded detectors and expected improvements in the theoretical understanding. This document summarises the physics reach of the HL-LHC in the realm of strong and electroweak interactions and top quark physics, and provides a glimpse of the potential of a possible further upgrade of the LHC to a 27 TeV $pp$ collider, the High-Energy LHC (HE-LHC), assumed to accumulate an integrated luminosity of 15 ab$^{-1}$.

We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

The new numerical approach that includes $$1\otimes 2$$ mechanisms is applied to double parton scattering (DPS) in W+dijet and Z+dijet final-state production in proton–proton collisions at the LHC. By using the underlying event (UE) simulation from a pythia 8.205 tune extracted in hadronic events, we show that, like in the case of a four-jet final state, the inclusion of $$1\otimes 2$$ mechanisms improves the description of experimental data measured at 7 TeV. The analysis is based on applying an event-by-event reweighting factor to a standard pythia 8.205 sample, by using the theoretical value of $$\sigma _\mathrm{eff}$$ , which includes corrections due to $$1\otimes 2$$ mechanisms. In addition, predictions for proton–proton collisions at a center-of-mass energy of 13 TeV are shown for DPS-sensitive observables. The relevant code, used for this analysis, is publicly available at the following link: http://desy.de/~gunnep/SigmaEffectiveDependence/ .

Comparisons of experimental data with theoretical predictions for collider processes containing hadronic jets rely on shower Monte Carlo event generators to include corrections to perturbative calculations from hadronization, parton showering, multiple parton collisions. We examine current treatments of these corrections and propose alternative methods to take into account nonperturbative effects and parton showering in the context of next-to-leading-order (NLO) event generators. We point out sizeable parton-showering corrections to jet transverse energy spectra at high rapidity, and discuss kinematic shifts in longitudinal momentum distributions from initial state showering in the case both of jet production and of heavy mass production at the Large Hadron Collider.

In the forthcoming high-luminosity phase at the LHC many of the most interesting measurements for precision QCD studies are hampered by conditions of large pile-up, particularly at not very high transverse momenta. We study observables based on measuring ratios of color-singlet currents via Higgs boson and Drell-Yan production, which may be accessed also at large pile-up, and used for an experimental program on QCD physics of gluon fusion processes in the LHC high-luminosity runs. We present results of Monte Carlo calculations for a few specific examples.

Multiple Partonic Interactions are often crucial for interpreting results obtained at the Large Hadron Collider (LHC). The quest for a sound understanding of the dynamics behind MPI - particularly at this time when the LHC is due to start its "Run II" operations - has focused the aim of this workshop. MPI@LHC2014 concentrated mainly on the phenomenology of LHC measurements whilst keeping in perspective those results obtained at previous hadron colliders. The workshop has also debated some of the state-of-the-art theoretical considerations and the modeling of MPI in Monte Carlo event generators. The topics debated in the workshop included: Phenomenology of MPI processes and multiparton distributions; Considerations for the description of MPI in Quantum Chromodynamics (QCD); Measuring multiple partonic interactions; Experimental results on inelastic hadronic collisions: underlying event, minimum bias, forward energy flow; Monte Carlo generator development and tuning; Connections with low-x phenomena, diffraction, heavy-ion physics and cosmic rays. In a total of 57 plenary talks the workshop covered a wide range of experimental results, Monte Carlo development and tuning, phenomenology and dedicated measurements of MPI which were produced with data from the LHC's Run I. Recent progress of theoretical understanding of MPI in pp, pA and AA collisions as well as the role of MPI in diffraction and small-x physics were also covered. The workshop forstered close contact between the experimental and theoretical communities. It provided a setting to discuss many of the different aspects of MPI, eventually identifying them as a unifying concept between apparently different lines of research and evaluating their impact on the LHC physics programme.

The CDF Associative-Memory device (AM), proven technology developed for the Silicon-Vertex-Trigger at the CDF experiment, is one of the proposed solutions at LHC for track reconstruction at level-1 in the HL-LHC upgrade, for very high-luminosity conditions (hundreds proton-proton collisions every 25 ns, at 5 × 1034 cm−2sec−1). This luminosity requires a drastic revision of the existing trigger strategies. In the framework of the CMS experiment, one of the identified challenges for future upgrades is the capability of using already at L1 the tracker information to trigger events. This strategy requires massive computing power to minimize the online execution time of complex tracking algorithms and the ``combinatorial challenge''. The AM allows to compare the tracker information of each event to pre-calculated ``expectations'' (pattern matching) in such a short time that tracks can contribute to the trigger decision. One of the main challenges for the CMS tracker is the latency due to the tracker data distribution to the AM processors. A very parallelized readout architecture and a possible layout are discussed.

By using predictions from the Pythia 8 Monte Carlo event generator, we determine the energy-dependent turn-over values (pT0) of the partonic cross section for the simulation of multiparton interactions. Since the observed energy dependence of the pT0 values is not well described by a power-law function, we introduce an additional energy-dependent term, to better describe the experimental observations in the energy range sqrt(s) = 0.3-13 TeV. We obtain a similar level of agreement for predictions using various parton densities.

We study contributions from nonperturbative effects and parton showering in NLO event generators, and present applications to jet final states. We find pT-dependent and rapidity-dependent corrections which can affect the shape of observed jet distributions at the LHC. We illustrate numerically the kinematic shifts in longitudinal momentum distributions from the implementation of energy-momentum conservation in collinear shower algorithms.

This thesis addresses in a very new and elegant way several measurements and the extraction of so-called double parton scattering. The new and elegant way lies in the combination of measurements and a

The CASTOR Calorimeter at the CMS experiment is an electromagnetic/hadronic calorimeter which covers the very forward region of the detector (-6.6 < eta < -5.2). CASTOR is a Cherenkov sampling calorimeter, consisting of quartz and tungsten plates, with an overall depth of 10 interaction lengths, able to detect penetrating cascade particles. It is segmented in 16 transversal and 14 longitudinal sections. Surrounding the beam pipe, its design is determined by space constraints and restricted to materials which tolerate a high radiation level. In this presentation we report on the operational experience and measurements with the CASTOR calorimeter during the 2010 data taking at the LHC, with proton-proton and heavy ion collisions. An overview of the broad physics program which can be accessed with CASTOR, as well as the status of published and ongoing physics analyses and detector studies are presented.

An overview of theoretical and experimental progress in double parton scattering (DPS) is presented. The theoretical topics cover factorization in DPS, models for double parton distributions and DPS in charm production and nuclear collisions. On the experimental side, CMS results for dijet and double J/ψ production, in light of DPS, as well as first results for the 4-jet channel are presented. ALICE reports on a study of open charm and J/ψ multiplicity dependence.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

ITFA, University of Amsterdam, Science Park 904, 1018 XE, Amsterdam, The Netherlands(Dated: October 27, 2014)An overview of theoretical and experimental progress in double parton scattering (DPS) is pre-sented. The theoretical topics cover factorization in DPS, models for double parton distributionsand DPS in charm production and nuclear collisions. On the experimental side, CMS results fordijet and double J= production, in light of DPS, as well as rst results for the 4-jet channel arepresented. ALICE reports on a study of open charm and J= multiplicity dependence.I. PROGRESS IN THE THEORY OFDOUBLE PARTON SCATTERINGA. Introduction

In the forthcoming high-luminosity phase of the LHC many of the most interesting measurements for precision QCD studies are hampered by large pile-up conditions, especially at not very high transverse momenta.However, with the recently discovered Higgs boson, which couples in the heavy top limit directly to gluons, we have access to a novel production process to probe QCD by a colour-singlet current.In this study we compare observables in Higgs boson and Drell-Yan production and investigate whether measuring ratios or subtractions can yield results that are stable in high pile-up environments, and yet sensitive to (small-p T ) QCD physics in gluon fusion processes.We present results of Monte Carlo event generator calculations for a few specific examples.

Various measurements, i.e., W + 2jets, 4 jets, photons + 3jets, WW, are performed to study the high pT/mass particle production from double parton scatterings. This talk will summarizes results from different DPS measurements. Presented at 7thMPI 7th International Workshop on Multiple Partonic Interactions at the LHC Study of high pT particle production from double parton 1 scatterings at the CMS experiment 2 Paolo Gunnellini1 3 1Deutsches Elektronen Synchrotron (DESY), Hamburg 4 1 on behalf of the CMS Collaboration 5

In this chapter the Large Hadron Collider (LHC) and the Compact Muon Solenoid (CMS) experiment are described; in particular, the parts of the detector relevant for the analyses of this thesis are treated in detail.

Our knowledge of the particle physics world is strongly connected to the formulation of the Standard Model (SM) [1]. The SM is a very successful theory which is able to describe a wide class of phenomenona undergone by elementary particles, by including a consistent picture of the interactions experienced by them. One of the considered interactions is called “strong interaction” and, as the name might suggest, it is the one with the largest intensity.

After the data unfolding, absolute and normalized differential cross sections are available at the stable particle level.

As explained in Chap. 1 , the theory of QCD is able to explain a wide collection of phenomena in particle physics, initiated by strong interactions between partons and consisting in final states of hadronic jets. Many QCD predictions concerning deep inelastic scattering of electron beams colliding on protons and jet physics give a good agreement over a large number of measurements.

With the results of the 4j and 2b2j scenarios, the collection of measurements in DPS-sensitive channels is largely enriched and additional interactions occurring in proton-proton collisions may be further investigated.

In this chapter, all possible experimental effects are described in full detail. The investigation of the detector effects has been performed in different steps.

A review of experimental measurements from the Compact Muon Solenoid Experiment at the LHC Run 1 is presented. A particular focus is given to jet results in the central and forward regions, and to measurements sensitive to the behaviour of small-x gluons inside the proton and to double parton scattering.

A measurement of the underlying event (UE) activity in proton-proton collisions is performed using events with charged-particle jets produced in the central pseudorapidity region (|η jet| 0.5 GeV, in the azimuthal region transverse to the highest pT jet direction. By further dividing the transverse region into two regions of smaller and larger activity, respec-

Using the ”Rivet and ”Professor framework, we construct a new PYTHIA 6 tune using the CTEQ6L1 PDF and two new PYTHIA 8 UE tunes (one using CTEQ6L1 and one using the HERAPDF1.5LO). By simultaneously fitting CDF data from collisions at 300 GeV, 900 GeV, and 1.96 TeV together with CMS data for pp collisions at 7 TeV, we test the Underlying Event (UE) models and constrain their parameters, allowing for more precise predictions at 13 TeV and 14 TeV. The consistency of these new tunes with measurements of double-parton scattering (DPS) is also investigated. DPS-based tunes are also extracted, relying on differential cross sections as a function of correlation observables, for the production of exactly four jets in proton-proton collisions. From this measurement it is found that the addition of parton showers to fixed-order matrix element calculations describe the measured differential cross sections in only some regions of phase space and that including a contribution from double parton scattering in the models brings the predictions closer to the data.

8th International Workshop on Multiple Partonic Interactions at the LHC, 8thMPI@LHC, San Cristobal de las Casas, Mexico, 28 Nov 2016 - 2 Dec 2016 ; (2016).

8th International Workshop on Multiple Partonic Interactions at the LHC, 8thMPI@LHC, San Cristobal de las Casas, Mexico, 28 Nov 2016 - 2 Dec 2016 ; (2016).

Measurements of double-differential inclusive jet cross sections as a function of jet transverse momentum p T and absolute jet rapidity |y| are presented for different collision energies.The analysis are based on proton-proton collisions collected by the CMS experiment.Jets are defined through the anti-k T clustering algorithm for different cone sizes.It is observed that predictions of perturbative quantum chromodynamics at next-to-leading order precision, complemented with nonperturbative corrections, are able to reproduce the measured data for the considered energies with a very good level of agreement.Parton-shower contributions are crucial for the description of jets, reconstructed with smaller cone sizes.

Using the "Rivet" and "Professor" framework, we construct a new PYTHIA 6 tune using the CTEQ6L1 PDF and two new PYTHIA 8 UE tunes (one using CTEQ6L1 and one using the HER-APDF1.5LO).By simultaneously fitting CDF data from collisions at 300 GeV, 900 GeV, and 1.96 TeV together with CMS data for pp collisions at 7 TeV, we test the Underlying Event (UE) models and constrain their parameters, allowing for more precise predictions at 13 TeV and 14 TeV.The consistency of these new tunes with measurements of double-parton scattering (DPS) is also investigated.DPS-based tunes are also extracted, relying on differential cross sections as a function of correlation observables, for the production of exactly four jets in proton-proton collisions.From this measurement it is found that the addition of parton showers to fixed-order matrix element calculations describe the measured differential cross sections in only some regions of phase space and that including a contribution from double parton scattering in the models brings the predictions closer to the data.

In the forthcoming high-luminosity phase of the LHC many of the most interesting measurements for precision QCD studies are hampered by large pile-up conditions, especially at not very high transverse momenta. However, with the recently discovered Higgs boson, which couples in the heavy top limit directly to gluons, we have access to a novel production process to probe QCD by a colour-singlet current. In this study we compare observables in Higgs boson and Drell-Yan production and investigate whether measuring ratios or subtractions can yield results that are stable in high pile-up environments, and yet sensitive to (small-$p_{\text{T}}$) QCD physics in gluon fusion processes. We present results of Monte Carlo event generator calculations for a few specific examples.

We improve the treatment of Multiple Parton Interactions (MPI) in \textsc{Pythia} by including the \12 mechanism and treating the \22 mechanism in a model-independent way. The \22 mechanism is calculated within the mean field approximation, and its parameters are expressed through Generalized Parton Distributions extracted from HERA data. The parameters related to the transverse parton distribution inside the proton are thus independent of the performed fit. The \12 mechanism is included along the lines of the recently developed perturbative QCD formalism. A unified description of MPI at moderate and hard transverse momenta is obtained within a consistent framework, in good agreement with experimental data measured at 7 TeV. Predictions are shown for the considered observables at 14 TeV. The corresponding code implementing the new MPI approach is available.

In this chapter, a description of how an event in particle physics is simulated is provided. The event simulation includes both the physics of the generated process, arising from a defined initial beam state and producing a bunch of particles in the final state, and the interactions of the final particles with the detector. The whole machinery uses the generation of random numbers through a Monte Carlo (MC) method, and it is generally divided in different steps. First of all, the physics process is generated by an event generator, which implements a ME for the hard scattering, interfaced with an UE simulation.

For a physics analysis, it becomes crucial to study the uncertainties which affect the measurements, in order to extract meaningful conclusions.

In this thesis, measurements of multijet channels in proton-proton collisions at 7 TeV, performed with the Compact Muon Solenoid at the Large Hadron Collider are presented.

In this chapter, the event reconstruction of data measured with the CMS experiment is described in full detail. From the huge amount of recorded data, it is important to extract compact information small in size, related to particles which have crossed the detector and generated the signal.

Measurements of differential cross sections for the production of at least four jets, two of them initiated by a b-quark, in proton-proton collisions are presented as a function of the transverse momentum p T and pseudorapidity η, together with the correlations in azimuthal angle and the p T -balance among the jets.The data sample was collected in 2010 at a center-of-mass energy of 7 TeV with the CMS detector at the LHC with an integrated luminosity of 3 pb -1 .The measurement, compared to predictions from different models, shows that the addition of parton showers to fixed-order matrix element calculations describe the measured differential cross sections in only some regions of phase space.Including a contribution from double parton scattering in the models improves the predictions.

Comparisons between data and theoretical predictions need to be performed in a consistent way: either, detector effects are added to any model predictions and curves are compared at detector level, or data are corrected to the stable particle level, where detector effects are removed; any event generator which includes parton evolution, hadronization and UE simulation, produces predictions at this level.

In this chapter, the selection of events at detector level is described in full detail.

Multiparton interactions are introduced in order to explain a wide range of phenomena in p-p collisions. We present the most recent CMS measurements sensitive to multiparton interactions and hard double parton scattering at 7 TeV. In particular, the W+dijet channel and a scenario with four light jets in the final state are described.

Latest tests of double parton scattering, underlying event tunes, minimum bias, and diffraction made by comparing the state-of-the-art theoretical predictions interfaced with up-to-date parton shower codes to the CMS Run I and Run II data are presented.Studies to derive and to test a new CMS PYTHIA 8 event tune obtained through jet kinematics in top quark pair events and global event variables are described.

The Phase I upgrade of the CMS Hadron Endcap Calorimeters consists of new photodetectors (Silicon Photomultipliers in place of Hybrid Photo-Diodes) and front-end electronics. The upgrade will eliminate the noise and the calibration drift of the Hybrid Photo-Diodes and enable the mitigation of the radiation damage of the scintillators and the wavelength shifting fibers with a larger spectral acceptance of the Silicon Photomultipliers. The upgrade also includes increased longitudinal segmentation of the calorimeter readout, which allows pile-up mitigation and recalibration due to depth-dependent radiation damage. As a realistic operational test, the responses of the Hadron Endcap Calorimeter wedges were calibrated with a 60Co radioactive source with upgrade electronics. The test successfully established the procedure for future source calibrations of the Hadron Endcap Calorimeters. Here we describe the instrumentation details and the operational experiences related to the sourcing test.

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 10^16 cm^-2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb^-1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiment's needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100x25 um^2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip, and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to F_eq = 3.6 10^15 cm-2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3.2 +\- 0.1 um is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5.0 +/- 0.2 um for a proton-irradiated sensor at F_eq = 2.1 10^15 cm-2 and a neutron-irradiated sensor at F_eq = 3.6 10^15 cm^-2.

Sensitivities studies of color re-connection (CR) effects in tt underlying events were performed for the fully leptonic and fully hadronic final states (FLFS and FHFS respectively) events. Effects of CR parameters were studied. Differences between predictions with and without CR were observed of ~ 8-15% for the investigated observables, charged particle multiplicity, charged particle average transverse momentum and transverse momentum sum. For different color re-connection models, effects around 5% were observed. No differences for predictions with and without CR between FLFS and FHFS were found for all the observables. This study shows the sensitivity of the UE observables to CR effects and may help to decrease the uncertainties due to the UE simulation in top mass measurements.

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 10^16 cm^-2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb^-1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiment's needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100x25 um^2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip, and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to F_eq = 3.6 10^15 cm-2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3.2 +\- 0.1 um is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5.0 +/- 0.2 um for a proton-irradiated sensor at F_eq = 2.1 10^15 cm-2 and a neutron-irradiated sensor at F_eq = 3.6 10^15 cm^-2.