A Study of Azimuthal Z-Jet Momentum Imbalance in Monte Carlo PbPb Collisions at Sqrt(Snn)
A Study of Azimuthal Z-Jet Momentum Imbalance in Monte Carlo PbPb Collisions at Sqrt(Snn)

Author: Stephen Keeton

Publisher:

Published: 2015

Total Pages: 158

ISBN-13:

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Jets have long been used as an effective probe for exploring the properties of the quark-gluon plasma (QGP) produced in high energy collisions of nuclei [1]. In heavy ion collisions some nucleons will undergo hard scattering, breaking apart and releasing their constituent high transverse momentum partons. These partons undergo hadronization due to the phenomenon of colour confinement. This is a process in which, as the constituent partons separate, the strong coupling constant increases until there is enough potential energy for it to be more energetically favourable to produce a quark-antiquark pair. This radiates more partons, predominantly collinear with their parent, forming jets of particles. As the energy of these particles decrease they will form colourless hadrons which can be detected. We set out with the aim to establish a groundwork for measuring the shape of the QGP by examining the energy loss of jets with respect to the azimuthal angle. By examining Z+jet events we aim to accurately measure the jet energy lost through jet quenching in the QGP. We expect jets which have traversed a larger distance in the QGP to lose more energy and thus an azimuthal anisotropy of jet energy loss will give us information on the shape of the produced QGP. While the latest run at the LHC did not yield many Z events from PbPb collisions [2] the next run should provide the data necessary for a complete analysis of this type. We will make use of a dijet enhanced Monte Carlo (MC) dataset in order to plan out the process and collect preliminary results.

Study of Jet Quenching with Z+jet Correlations in PbPb and Pp Collisions at $\sqrt{s_{NN}}$
Study of Jet Quenching with Z+jet Correlations in PbPb and Pp Collisions at $\sqrt{s_{NN}}$

Author:

Publisher:

Published: 2017

Total Pages:

ISBN-13:

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The production of jets in association with Z bosons, reconstructed via the mu+mu- and e+e- decay channels, is studied in pp and, for the first time, in PbPb collisions. Both data samples were collected by the CMS experiment at the LHC, at a center-of-mass energy of 5.02 TeV. The PbPb collisions were analyzed in the 0-30% centrality range. The back-to-back azimuthal alignment was studied in both pp and PbPb collisions for Z bosons with transverse momentum ptz> 60 GeV/c and a recoiling jet with ptj> 30 GeV/c. The pt imbalance, xjz= ptj/ptz, as well as the average number of jet partners per Z, rjz, were studied in intervals of ptz, in both pp and PbPb collisions. The rjz is found to be smaller in PbPb than in pp collisions, which suggests that in PbPb collisions a larger fraction of partons, associated with the Z bosons, lose energy and fall below the 30 GeV/c ptj threshold.

Decomposing Transverse Momentum Balance Contributions for Quenched Jets in PbPb Collisions at $ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}
Decomposing Transverse Momentum Balance Contributions for Quenched Jets in PbPb Collisions at $ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}

Author:

Publisher:

Published: 2016

Total Pages:

ISBN-13:

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Interactions between jets and the quark-gluon plasma produced in heavy ion collisions are studied via the angular distributions of summed charged-particle transverse momenta (pT) with respect to both the leading and subleading jet axes in high-pt dijet events. The contributions of charged particles in different momentum ranges to the overall event pt balance are decomposed into short-range jet peaks and a long-range azimuthal asymmetry in charged-particle pT. The results for PbPb collisions are compared to those in pp collisions using data collected in 2011 and 2013, at collision energy $ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=2.76 $ TeV with integrated luminosities of 166 [mu]b-1 and 5.3 pb-1, respectively, by the CMS experiment at the LHC. Furthermore, measurements are presented as functions of PbPb collision centrality, charged-particle pt, relative azimuth, and radial distance from the jet axis for balanced and unbalanced dijets.

Observation and Studies of Jet Quenching in PbPb Collisions at Nucleon-nucleon Center-of-mass Energy
Observation and Studies of Jet Quenching in PbPb Collisions at Nucleon-nucleon Center-of-mass Energy

Author:

Publisher:

Published: 2011

Total Pages: 26

ISBN-13:

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Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

Study of Jet Quenching Using Z-Jet Events in Heavy Ion and Proton-proton Collisions Using the CMS Detector
Study of Jet Quenching Using Z-Jet Events in Heavy Ion and Proton-proton Collisions Using the CMS Detector

Author: Ana Snjegota

Publisher:

Published: 2016

Total Pages: 72

ISBN-13:

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The aim of this study was to investigate the phenomenon of jet quenching due to the formation of the quark-gluon plasma in heavy ion and proton-proton collisions. This was done by comparing the transverse momentum, pT , ratio between a jet of hadronic particles, and a Z boson in both Monte Carlo simulations and real datasets, collected during the 2015 run of the Large Hadron Collider, using the Compact Muon Solenoid detector. The pT imbalance was studied in three di erent regions, namely for events where the Z boson had transverse momentum pT > 30GeV, pT > 60GeV and pT > 100GeV. The results show that there is a signi cant suppression of the jet pT in central heavy ion collisions compared to the proton-proton collisions, and the pT ratio decreases with higher initial pT.

Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at $ \sqrt{s_{\mathrm{NN}}}
Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at $ \sqrt{s_{\mathrm{NN}}}

Author:

Publisher:

Published: 2016

Total Pages: 39

ISBN-13:

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In this study, the quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity ([Delta][eta]) and relative azimuthal angle ([Delta][Phi]) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pT) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pT, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pT. A centrality-dependent excess of low-pT particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pT particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of [Delta][eta] ≈ 1 and [Delta][Phi] ≈ 1.

Study of Jet Transverse Momentum and Jet Rapidity Dependence on Dijet Azimuthal Decorrelations
Study of Jet Transverse Momentum and Jet Rapidity Dependence on Dijet Azimuthal Decorrelations

Author:

Publisher:

Published: 2012

Total Pages: 109

ISBN-13:

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In a collision experiment involving highly energetic particles such as hadrons, processes at high momentum transfers can provide information useful for many studies involving Quantum Chromodynamics (QCD). One way of analyzing these interactions is through angular distributions. In hadron-hadron collisions, the angular distribution between the two leading jets with the largest transverse momentum (pT) is affected by the production of additional jets. While soft radiation causes small differences in the azimuthal angular distribution of the two leading jets produced in a collision event, additional hard jets produced in the event have more pronounced influence on the distribution of the two leading jets produced in the collision. Thus, the dijet azimuthal angular distribution can serve as a variable that can be used to study the transition from soft to hard QCD processes in a collision event. This dissertation presents a triple-differential study involving the azimuthal angular distribution and the jet transverse momenta, and jet rapidities of the first two leading jets. The data used for this research are obtained from proton-antiproton (p$\bar{p}$) collisions occurring at a center of mass energy of 1.96TeV, using the DØ detector in Run II of the Tevatron Collider at the Fermi National Accelerator Laboratory (FNAL) in Illinois, USA. Comparisons are made to perturbative QCD (pQCD) predictions at next-to-leading order (NLO).

Measurement of Dijet Azimuthal Decorrelation in Pp Collisions at $\sqrt{s}$
Measurement of Dijet Azimuthal Decorrelation in Pp Collisions at $\sqrt{s}$

Author:

Publisher:

Published: 2016

Total Pages:

ISBN-13:

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A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.

Ultrarelativistic Heavy-Ion Collisions
Ultrarelativistic Heavy-Ion Collisions

Author: Ramona Vogt

Publisher: Elsevier

Published: 2007-06-04

Total Pages: 489

ISBN-13: 0080525369

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This book is designed for advanced undergraduate and graduate students in high energy heavy-ion physics. It is relevant for students who will work on topics being explored at RHIC and the LHC. In the first part, the basic principles of these studies are covered including kinematics, cross sections (including the quark model and parton distribution functions), the geometry of nuclear collisions, thermodynamics, hydrodynamics and relevant aspects of lattice gauge theory at finite temperature. The second part covers some more specific probes of heavy-ion collisions at these energies: high mass thermal dileptons, quarkonium and hadronization. The second part also serves as extended examples of concepts learned in the previous part. Both parts contain examples in the text as well as exercises at the end of each chapter. - Designed for students and newcomers to the field- Focuses on hard probes and QCD- Covers all aspects of high energy heavy-ion physics- Includes worked example problems and exercises