UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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Subject: search.filters.subject.Compact Muon Solenoid

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    Jet Production Cross Section Measurement In √ s = 5.02 Tev pp Collisions
    (2021) Baron, Owen David Cadwalader; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The study of jets offers insights into the nature of the basic partons composing matter, and enables further studies into the nature of the universe. This analysis presents the double-differential production cross section of radius parameter R = 0.3 proton-proton jets in units of pseudorapidity and transverse momentum at √ s = 5.02 TeV, measured in the Compact Muon Solenoid detector at the Large Hadron Collider experiment located at CERN. Jets are reconstructed using Particle Flow and the anti-kT algorithms. The methodology of correcting the detector response through Jet Energy Corrections and Bayesian unfolding is described with a detailed explanation. The results from data recorded in CMS in 2015 are shown and compared with leading-order theory-based simulated PYTHIA8 Monte Carlo events.
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    Nuclear Modification Factor of High Momentum Jets in PbPb Collisions
    (2013) Lu, Ying; Mignerey, Alice; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    According to quantum chromodynamics (QCD), the release of quarks and gluons creates a new form of matter, the quark gluon plasma (QGP), expected to occur in relativistic heavy-ion collisions at high energies. The structure and dynamics of the QGP can be studied using partonic interactions at large momentum transfers. This was studied at the Relativistic Heavy Ion Collider starting in 2002 utilizing AuAu collisions at 200 GeV center-of-mass. In this analysis, fully reconstructed jets in pp and PbPb collisions at 2.76 TeV center-of-mass energy are analyzed with the CMS detector at the Large Hadron Collider (LHC) in CERN. The ratio of inclusive reconstructed jet transverse momenta spectra of PbPb collisions to that of proton+proton (pp) collisions is defined as jets nuclear modification factor (RAA) and it is studied to quantify the medium modification within transverse momenta above 100GeV/c. Jet RAA results are compared for three different unfolding methods: Bayesian Unfolding, bin-by-bin Unfolding and Generalized Singular Value Decomposition (GSVD) Unfolding, as well as corrections performed with pp data smearing. A jet RAA of approximately 0.5 is observed in the most central collisions and close to unity in the most peripheral collisions without a strong indication of the transverse momenta (pT) dependence. A suppression of high pT jets is observed in central PbPb collisions in comparison to peripheral collisions. This is consistent with the observation of jet quenching.
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    Using machine learning to measure the cross section of top quark pairs in the muon+jets channel at the Compact Muon Solenoid
    (2011) Kirn, Malina Aurelia; Hadley, Nicholas; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The cross section for pp to top-antitop production at a center of mass energy of 7 TeV is measured using a data sample with integrated luminosity 36.1 inverse pb collected by the CMS detector at the LHC. The analysis is performed on a computing grid. Events with an isolated muon and three hadronic jets are analyzed using a multivariate machine learning algorithm. Kinematic variables and b tags are provided as input to the algorithm; output from the algorithm is used in a maximum likelihood fit to determine top-antitop event yield. The measured cross section is 151 +/- 15(stat.) +35/-28(syst.) +/- 6(lumi.) pb.