Heavy-ion Results from CMS

<p>This thesis uses genetic Tag and probe method to study muon ID efficiency in Compact Muon Solenoid(CMS) Detector. CMS is one of the main detectors in Large Hadron Collider, which is the world’s largest and most powerful particle collider. The main object of the CMS Collaboration is to inverstigate physics underlying elec- troweak symmetry breaking. Moreover, the CMS detector allows experimental par- ticle physicists to perform various experiments which possibly produce new physics signatures beyond the Standard Model (SM). In order to detect and study these sig- natures, it requires the identification and accurate and precise measurement of muon efficiency. To achieve the measurement, a genetic data-driven approach, Tag and Probe method, is used. This method is widely used in CMS community to measure any user defined object efficiency. Typical observable that is used by this method is di-object resonances like Z or J/Psi. In this thesis, Tag and Probe method employs J/Psi resonances to measure muon Soft and Tight ID efficiency, at proton proton collision at √s = 13 GeV .</p>

<p>This thesis contains both physics analysis and hardware studies. It consists of two primary sections: the results of a search for heavy Majorana mass neutrinos, using the event signature of same (like) sign charged electron pairs ($e^{\pm} e^{\pm}$ ) and two jets, and the results of studies to upgrade the Hadronic Forward (HF) and Hadronic Endcap (HE) subdetectors in the Compact Muon Solenoid (CMS) detector in response to the high intensity proton-proton collisions generated at the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN, Conseil Europ\'{e}en pour la Recherche Nucl\'{e}aire).</p> <p>In this search for Majorana mass neutrinos, same sign dielectron ($e^{\pm} e^{\pm}$) + dijet events in the final state have been considered as a signature for neutrino particles. The analyzed data corresponds to an integrated luminosity of 19.7 fb\textsuperscript{-1} of proton-proton collisions at a center of mass energy of \begin{math}\sqrt{s} = 8\ TeV \end{math}, collected using the CMS detector during the 2012 operation at the LHC. Monte Carlo simulations accounting for the theoretical expectations of the Standard Model (SM) and the detector limitations are used to prototype the experiment and to test proposed analysis steps. No excess of events is observed in the data beyond the expected SM background. Upper limits are set on the mixing element squared, $|{V}_{eN}|^{2}$, of the heavy Majorana neutrino with standard model neutrinos, as a function of Majorana neutrino mass for masses in the range of 40-500 $GeV/c^2$.</p> <p>The detector upgrade search comprises three sections of this thesis. The first section describes the test results of 1785 multianode Hamamatsu R7600U-200-M4 photomultiplier tubes (PMT) in numerous parameters such as gain, dark current, and timing characteristics, which provide insights on the expected performance of the upgraded CMS-HF detector. These PMTs replaced the previous single anode R7525 PMTs because the glass windows of previous PMTs are the source of Cherenkov radiation, which causes a background noise in the experiment. The second section reports characterization results of two types of PMTs in a novel operation mode for Secondary Emission (SE) Ionization Calorimetry, which is a novel technique to measure electromagnetic shower particles in extreme radiation environments.</p> <p>The third section presents the test results of novel scintillating materials for CMS experiment in specific and future particle accelerators in general. These materials are Polyethylene Naphthalate (PEN), Polyethylene Terephthalate (PET), high efficiency mirror (HEM) and quartz plates with various organic and inorganic coating materials such as p-Terphenyl (pTp), Anthracene and Gallium-doped Zinc Oxide (ZnO:Ga). We have investigated them for radiation hardness, light yield, timing characteristics, and scintillation and transmission properties.</p>

The Large Hadron Collider (LHC) at CERN sitting astride the Franco-Swiss border near Geneva has accumulated the proton and proton collision data corresponding to an integrated luminosity of around 5 fb−1 at the center of mass energy 7 TeV in 2011 and around 20 fb−1 at 8 TeV in 2012 with the Compact Muon Solenoid (CMS) detector. The CMS detector is designed to investigate the wide range of particle physics including testing perturbative QCD and searching for Brout-Englert-Higgs (BEH) boson as well as new physics phenomena beyond the Standard Model. Observation of a new boson has moved the phase from hunting for the SM BEH boson to evaluating the consistency of this new particle with the SM expectation. The latest results from the CMS collaboration will be presented.

In part I of this thesis, I perform a search for the Standard Model Higgs boson decaying into two photons using 5.08 fb-1 of data collected by the Compact Muon Solenoid (CMS) detector in 2011 at a center-of-mass energy √(s)= 7 TeV. The result of this search is interpreted as a local excess in the mass around 123 GeV/c2 with an significance of 3.3 standard deviation. This excess was later confirmed in the data in 2012, and was an important contribution to the CMS discovery paper published in 2012. This search makes use of the excellent energy resolution of the CMS crystal electromagnetic calorimeter (ECAL). The energy intercalibration of approximately 76,000 crystals is crucial to improve the resolution performance. I describe in detail a novel intercalibration method using neutral π0(η) → γγ decays. This method was the first one in CMS to reach 0.5% calibration precision in the central part of ECAL with pseudorapidity less than 1. This calibration improved the Higgs to two photons search sensitivity by about 30%, compared to the precalibration performed before the installation of ECAL in CMS detector. In part II of this thesis, I perform a search for an excited muon decaying into one muon and one photon using 36 pb-1 of data collected in 2010 at √(s)= 7 TeV. The result of this search indicates no evidence for excited muons. I report the first upper limits on single excited muon production cross section at this collision energy, and exclude a new region of the parameter space of compositeness scale and excited muon mass. Assume the compositness scale is the same as the excited muon mass, excited muons are excluded below 1090 GeV/c2 at the 95% confidence level, representing the most stringent limits, as of the date when the analysis was first published.

Recent results on heavy-ion physics at the LHC (CERN) by the Compact Muon Solenoid (CMS) collaboration are analyzed. The tests of quark-gluon plasma carried out with the CMS detector provide valuable information about the behavior of matter in the extreme regime of very high energy nucleus-nucleus collisions.

The High Luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of around 5×1034 cm−2s−1 and 3000 fb−1, respectively, from 2025 to 2035. During this operational period, an average of 140 to 200 collisions per bunch-crossing (pile up) is expected, posing a challenge to the event reconstruction. In order to cope with these extreme pile up conditions, harsh environment, and increased data rates, the Compact Muon Solenoid (CMS) detector is undergoing a radical Phase II upgrade program. In the barrel region of the CMS electromagnetic calorimeter (ECAL), the lead tungstate crystals and avalanche photodiodes (APDs) will keep performing well and will therefore be maintained, while the entire readout and trigger electronics will be replaced. A dual gain trans-impedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be installed. The noise increase in the APDs, due to radiation-induced dark current, will be contained by reducing the temperature at which ECAL is operated. The trigger decision will be moved off-detector and performed by powerful and flexible FPGA processors, allowing for more sophisticated trigger algorithms to be applied. The upgraded ECAL will be capable of high-precision energy measurements and will greatly improve the time resolution for photons and electrons above 10 GeV. Together with the introduction of a new timing detector designed to perform timing measurements with the resolution of a few tens of picoseconds for minimum ionizing particles, the CMS detector will be able to precisely reconstruct the primary interaction vertex under the described pile up conditions.

The Compact Muon Solenoid (CMS) detector is one of the two multi-purpose experiments at the Large Hadron Collider (LHC) and has a broad physics program. Many aspects of this program depend on our ability to trigger, reconstruct and identify events with final state electrons, positrons, and photons with the CMS detector with excellent efficiency and high resolution. We present the full process of electron and photon reconstruction in CMS, starting from tracker hits and energy deposits in the electromagnetic calorimeter, the methods to achieve the ultimate precision in Run II energy measurements, the identification strategies (based both on cut-based approach and on multivariate analysis) to discriminate prompt electrons and photons from background, and the methods to estimate the associated systematic uncertainties. Finally the performance on benchmark channels (such as Z → e+e−) will be shown.

The Compact Muon Solenoid (CMS) detector is one of the two multi-purpose experiments at the Large Hadron Collider (LHC) and has a broad physics program. Many aspects of this program depend on our ability to trigger, reconstruction and identify events with final state muons in a wide range of momenta, from few GeV to the TeV scale. In this talk we present the full process of muon reconstruction in CMS, both offline and online. The identification and isolation strategies to discriminate prompt muons from background, and their performance with 13 TeV data collected with the CMS experiment.

Quarkonia are most important probes of the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. The Compact Muon Solenoid (CMS) detector is well suited to measure quarkonia via their decays to dimuon channel. This writeup summarizes quarkonium measurements in pp and PbPb collisions by CMS detector at \(\sqrt{s_{NN}} = 2.76~\mathrm {TeV}\) and \(\sqrt{s_{NN}} = 5.02~\mathrm {TeV}\).

The Compact Muon Solenoid (CMS) detector is one of the 4 detectors at the CERN LHC to study the Standard Model (SM) and even searching for signatures of new physics produced in high-energy collisions in the LHC. As many of the signatures in both SM and new physics include muons, it is crucial to possess high performance of muon identification and reconstruction. The performance of CMS muon identification and reconstruction is studied based on the run 2 data collected with the CMS detector at $\sqrt{s} = 13 ~\mathrm{TeV}$. The identification and reconstruction efficiencies are measured using tag and probe method. As High-Level Trigger (HLT) has made improvements in its algorithms during the run 2, we also highlight its upgraded feature by comparing with the previous algorithm.

A temperature monitoring system based on fibre Bragg grating (FBG) fibre optic sensors has been developed for the gas electron multiplier (GEM) chambers of the Compact Muon Solenoid (CMS) detector. The monitoring system was tested in prototype chambers undergoing a general test of the various technological solutions adopted for their construction. The test lasted about two years and was conducted with the chambers being installed in the CMS detector and operated during regular experimental running. In this paper, we present test results that address the choice of materials and procedures for the production and installation of the FBG temperature monitoring system in the final GEM chambers.

A search for supersymmetry is presented based on proton-proton collision events containing identified hadronically decaying top quarks (i.e., events with no identified leptons), and an imbalance EmissT in transverse momentum. The data were collected with the Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) at a center-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb-1. The 84 exclusive search regions are defined in terms of the multiplicity of bottom quark jet and top quark candidates, the missing energy, the scalar sum of jet transverse momenta HT, and the transverse mass variable sensitive to the pair production of heavy particles, each of which decays into an invisible particle MT2. A novel and robust top quark reconstruction algorithm which is based on multivariate approach and is capable of identifying top quarks in the wide spectrum of top quark transverse momentum is developed. Methods in the modeling of events arising from quantum chromodynamics and electroweak boson production, which are major backgrounds in searches for new physics at the LHC, are also presented. No statistically significant excess of events is observed relative to the expectation from the standard model. Discussion of the non-excluded regions of the model parameter space is given. Lower limits on the masses of supersymmetric particles are determined at 95% confidence level in the context of simplified models with top quark production. For a model with direct top squark pair production followed by the decay of each top squark to a top quark and a neutralino, top squark masses up to 1020 GeV and neutralino masses up to 430 GeV are excluded. For a model with pair production of gluinos followed by the decay of each gluino to a top quark-antiquark pair and a neutralino, gluino masses up to 2040 GeV and neutralino masses up to 1150 GeV are excluded. These limits extend previous results obtained with 8 TeV data and 2.3 fb-1 13 TeV data.

The success of the first three years of operations of the CERN Large Hadron Collider (LHC) at center-of-mass energies of 7 TeV and 8 TeV radically changed the landscape of searches for new physics beyond the Standard Model (BSM) and our very way of thinking about its possible origin and its hiding place. Among the paradigms of new physics that have been probed quite extensively at the LHC, are various models that predict the existence of extra spatial dimensions. In this review, the current status of searches for extra dimensions with the Compact Muon Solenoid (CMS) detector is presented, along with prospects for future searches at the full energy of the LHC, expected to be reached in the next few years.

The status of CMS jet simulations and physics analysis in heavy ion collisions is presented. Jet reconstruction and high-pT particle tracking in the high multiplicity environment of heavy ion collisions at the LHC using the CMS calorimetry and tracking system are described. The Monte Carlo tools used to simulate jet quenching are discussed.

The present article gives a brief account of some interesting results obtained most recently in studying heavy-ion physics—in particular, quark–gluon matter—with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC).