Browsing by Subject "LHC"
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Item The differential shape of the Z to ee cross-section as a function of Z rapidity(2011-05) Haupt, Jason AnthonyBefore the LHC discovers new physics and new particles, the detectors needed to undergo commissioning. The detection and measurement of Standard Model processes was one way to validate the detector response. Some benefits of the validation procedure were accurate predictions of signals and backgrounds. The rapidity shape of the Z boson was used as a probe into the Probability Distribution Functions of the proton. This thesis discusses the differential Z cross-section measurement with 36 pb^-1 of integrated luminosity acquired at the LHC on the CMS detector in 2010 at a center of mass of 7 TeV.Item Measurement of the Associated Production of a Z Boson with a J/psi Meson with the CMS Experiment at a Center-of-Mass Energy of 8 TeV(2016-09) Turkewitz, JaredThe associated production of a Z boson and a J/psi meson provides information about the production mechanisms of quarkonium. A measurement of the associated production of a Z boson, which decays to leptons, and a J/psi meson, which decays to muons, relative to the inclusive production of a Z boson, which decays to leptons, is presented. The measurement was made using the full 19.7 inverse femtobarns of proton-proton collision data collected at a center-of-mass energy of 8 TeV by the Compact Muon Solenoid detector at the Large Hadron Collider. The associated production is presented for both prompt and nonprompt J/psi, as a function of the transverse momentum of the J/psi meson. The associated production cross sections of a Z that decays to two muons or to two electrons, and a prompt or nonprompt J/psi that decays to two muons, relative to the inclusive production cross section of a Z that decays to two muons or to two electrons, are measured.Item A measurement of the isolated photon cross section at CMS with square root of s = 7 TeV(2012-09) DeBenedetti, AbrahamWe measure the differential cross section for the inclusive production of isolated prompt photons. This measurement uses data recored by the CMS detector at the LHC in 2010 with proton-proton collisions having a center of mass energy of 7 TeV. The measurement of photon production at the LHC adds to our understanding of the Standard Model and is important for future investigations of new physics. The cross section is compared to the Standard Model with next-to-leading-order perturbative QCD calculations.Item A Precision Measurement Of The Mass Of The Higgs Boson In The Two Photon Decay Channel With The Cms Experiment.(2020-05) Hansen, PeterA measurement of the Higgs boson mass is presented in this thesis. The measurement was performed using 35.9/fb integrated luminosity of proton-proton collision data delivered by the LHC with a center-of-mass energy of 13 TeV and recorded by the CMS experiment during 2016. This thesis describes the improved measurement of the electron and photon energy scale and resolution using the electromagnetic calorimeter and the new analysis techniques used to improve the precision of the Higgs boson mass measurement. The Higgs boson mass is measured to be 125.78 ± 0.26 GeV. When combined with the H → ZZ*→ 4l decay channel and the data collected in 2011 and 2012, a value of 125.38 ± 0.14 GeV is found. This is currently the most precise measurement of the mass of the Higgs boson.Item Search for Disappearing Muons via Fixed-Target Interactions in the CMS Calorimeters(2023-12) Revering, MichaelWhile strong evidence for the existence of dark matter has been found in astronomicalobservations and simulations of galaxy structure formation and cosmic baryogenesis, no repeatable observations have been made of its potential non-gravitational interactions. The high energy interactions within particle accelerators present an environment where these dark matter interactions may be produced and their existence inferred from visible signatures in detectors. Traditional searches for collider-based dark matter require either visible final states or additional high-energy recoil particles to tag potential dark matter interactions, greatly lowering their selection efficiency. In this work I present a search for a dark-matter-like signal in proton-proton collisions at a center of mass energy of 13 TeV using the CMS detector at the CERN LHC, using tag-and-probe techniques to select for interactions of standard-model muons with the detector material. For dark matter models without visible decay products, these interactions are characterized by muon tracks which ‘disappear’, losing large amounts of energy without associated deposits in the calorimeters. The analysis is performed on the data set collected using the CMS experiment during 2018, corresponding to an integrated luminosity of 60.2fb−1. By using CMS as a fixed target experiment the inefficiency of selecting non-visible signatures in the initial collision can be avoided, extending the CMS sensitivity to dark matter models with hidden-sector decays or long lifetimes.Item Search for heavy stable charged particles at the CMS experiment(2012-10) Cooper, Seth Isaacmethod of searching for Heavy Stable Charged Particles (HSCP) using dE/dx and momentum measurements from the CMS inner tracking system is presented. The shape of the dE/dx distribution is used to distinguish background from signal, in combination with slicing the data into bins of pseudorapidity and number of dE/dx measurements, which together extend and improve on a previous analysis conducted as a counting experiment. In particular, the expected minimum cross section to make a discovery of 5-sigma significance is reduced, and expected upper limits are more restrictive. The data are consistent with the background-only hypothesis and are used to set upper limits on the production cross section as a function of mass for several different HSCP models. The data sample used was collected by the CMS detector in 2011 pp collisions at sqrt(s) = 7 TeV, corresponding to approximately 5/fb.Item Search for Long-Lived Neutral Particles in Final States with Delayed Photon and Missing Transverse Energy from Proton-Proton Collisions Using the CMS detector.(2015-11) Tambe Ebai, NorbertWe perform a search for long-lived neutral particles in final state with delayed photons and large missing transverse energy produced in LHC proton-proton collisions at center-of-mass energy, $\sqrt{s} = 8$TeV. Capitalizing on the excellent timing resolution of the CMS Electromagnetic Calorimeter the search uses photon time measurements made by the Electromagnetic Calorimeter as the main search quantity. We found a single event consistent with our background expectations from the Standard Model and set a model-independent upper limit of 4.37 on number of signal events. We also interpret our results in the context of the SPS8 benchmark GMSB model and show that neutralinos with mean lifetime, $\tau_{\PSneutralinoOne} \leq 45$ns, and mass, $m_{\PSneutralinoOne} \leq 300$GeV/c^{2}, or effective Supersymmetry breaking energy scale, $\Lambda \leq 220TeV$, are ruled out of existence at 95\% $CL_{S}$ confidence level. The exclusion limit on the product of the production cross-section and branching ratio of the neutralino to photon and gravitino decay channel, $\sigma_{(\PSneutralinoOne \rightarrow \gamma + \tilde{G})}\times BR$, for different lifetimes and masses is derived. Our results confirm for the first time that the CMS Electromagnetic Calorimeter provides good sensitivity to search for long-lived neutral particles with lifetimes up to $40$ns and masses up to $300$GeV/c^{2}using only timing measurements.Item Search for Right-Handed Neutrinos and Weak Bosons at CMS with the LHC at √s = 13 TeV and an integrated luminosity of 137 fbᐨ¹(2020-12) Evans, AndrewThis thesis presents the most expansive limits on the WR decay to two muons or electrons, and two jets at CMS. Left-right symmetric extensions to the Standard Model are motivated and presented giving rise to the purpose of this search. New techniques in boosted jet reconstruction are employed to expand past analytical approaches to now include much lighter NR hypotheses. With a larger signal acceptance compared to previous analyses, a new signal selection strategy is developed and explained. Then, standard model backgrounds for this analysis are discussed and estimated using several control regions. Data collected by the CMS collaboration over three years of Run II for a total of 137 fbᐨ¹ is combined and limits are set on the WR mass at 4-5 TeV and 4-5.5 TeV for the electron and muon flavor search respectively for NR masses ranging between 100-3000 GeV.