Measurements of Upsilon Meson Suppression in Heavy Ion Collisions with the CMS Experiment at the LHC

Measurements of Upsilon Meson Suppression in Heavy Ion Collisions with the CMS Experiment at the LHC
Author: Nicolas Filipovic
Publisher:
Total Pages: 0
Release: 2015
Genre:
ISBN:

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Measurements of Upsilon suppression in ultrarelativistic heavy ioncollisions are key to understanding the hot and deconfined phase ofmatter called Quark-Gluon Plasma (QGP). The cross section of Upsilonstates Y(nS) are measured in proton-proton collisions and in lead-leadcollisions at the centre-of-mass energy of 2.76 TeV per nucleonpair. Individual states are measured through their dimuon decaychannel using the Compact Muon Solenoid (CMS) at CERN. The crosssections measured in pp and PbPb are compared thanks to the nuclearmodification factor, R_{AA}. This observable is computed forUpsilon(1S) and Upsilon(2S) in several bins of transverse momentum,rapidity and centrality of the collision. An upper limit on theproduction of Upsilon(3S) in PbPb is estimated. These measurementsexhibit a clear and ordered suppression pattern, consistent with thehypothesis of sequential melting of quarkonia in the QGP. The measuredUpsilon(1S) and Upsilon(2S) suppressions are observed to beindependent of transverse momentum and rapidity. Comparisons withavailable phenomenological models are presented, however fail toreproduce the full set of observations. This novel measurement thusprovides new constraints on the modeling of heavy quark deconfinement.

Study of High Transverse Momentum Charged Particle Suppression in Heavy Ion Collisions at LHC

Study of High Transverse Momentum Charged Particle Suppression in Heavy Ion Collisions at LHC
Author: Andre Sungho Yoon
Publisher:
Total Pages: 284
Release: 2012
Genre:
ISBN:

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The charged particle spectrum at large transverse momentum (PT), dominated by hadrons originating from parton fragmentation, is an important observable for studying the properties of the hot, dense medium produced in high-energy heavy-ion collisions. The study of the modifications of the PT spectrum in PbPb compared to pp collisions at the same collision energy can shed light on the detailed mechanism by which hard partons lose energy traversing the medium. In this thesis, the transverse momentum spectra of charged particles in pp and PbPb collisions at [square root of]Snn = 2.76 TeV measured up to PT = 100 GeV/c with the CMS experiment at the Large Hadron Collider (LHC) are presented. In the transverse momentum range PT = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7 compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. At higher PT, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with PT in the range PT = 40-100 GeV/c. A simple modeling of the parton energy loss applied to the PYTHIA Monte-Carlo (MC) reveals that the charged particle spectrum with the pQCD-motivated fractional parton energy loss can describes the shape of the measured suppression well in the range PT = 5-100 GeV/c.

Strange and Non-Strange D-meson Production in pp, p-Pb, and Pb-Pb Collisions with ALICE at the LHC

Strange and Non-Strange D-meson Production in pp, p-Pb, and Pb-Pb Collisions with ALICE at the LHC
Author: Fabrizio Grosa
Publisher: Springer Nature
Total Pages: 227
Release: 2021-04-17
Genre: Science
ISBN: 3030711315

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This thesis provides a comprehensive view of the physics of charmed hadrons in high-energy proton-proton and heavy-ion collisions. Given their large masses, charm quarks are produced in the early stage of a heavy-ion collision and they subsequently experience the full system evolution probing the colour-deconfined medium called quark-gluon plasma (QGP) created in such collisions. In this thesis, the mechanisms of charm-quark in-medium energy loss and hadronisation are discussed via the measurements of the production of charm mesons with (Ds+) and without (D+) strange-quark content in different colliding systems, using data collected by the ALICE experiment at the CERN LHC. The participation of the charm quark and its possible thermalisation in the QGP are studied via measurements of azimuthal anisotropies in the production of D+ mesons. Finally, the prospects for future measurements with the upgraded ALICE experimental apparatus and with more refined machine learning techniques are presented.

Study of the Inclusive Beauty Production at CMS and Construction and Commissioning of the CMS Pixel Barrel Detector

Study of the Inclusive Beauty Production at CMS and Construction and Commissioning of the CMS Pixel Barrel Detector
Author: Lea Caminada
Publisher: Springer Science & Business Media
Total Pages: 159
Release: 2012-02-23
Genre: Science
ISBN: 3642245617

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This thesis describes one of the first measurements at the CERN LHC -- the world's largest and highest-energy particle collider. The CMS collision data is analyzed, and results in the first measurement of the inclusive b cross section using semileptonic decays at a center of mass energy of 7 TeV.

Characterization of Jets in Heavy Ion Collisions Using Photons at the LHC with the CMS Detector

Characterization of Jets in Heavy Ion Collisions Using Photons at the LHC with the CMS Detector
Author: Richard Alexander Barbieri
Publisher:
Total Pages: 138
Release: 2017
Genre:
ISBN:

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Using the CMS detector at the LHC, a quantitative study of jet energy loss and angular deflection inside the high energy-density medium formed in PbPb collisions is made. Photons are used to measure the initial state of a color-charged probe while jet reconstruction is used to measure the final state. Significant loss of energy to the medium as a function of initial parton momentum is observed, while no significant angular deflection is found.

Measurements of Production and Decay Properties of Bs Mesons Decaying Into J/psi Phi with the CMS Detector at the LHC

Measurements of Production and Decay Properties of Bs Mesons Decaying Into J/psi Phi with the CMS Detector at the LHC
Author: Giordano Cerizza
Publisher:
Total Pages: 292
Release: 2012
Genre:
ISBN:

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The production of hadrons containing b-quarks has been measured in proton anti-proton collisions up to center-of-mass energies of 1:96 TeV at the Tevatron. Information at lower energy is provided by electron-positron collision experiments. The underlying theory of hadronic interactions is tuned to those data but cannot reliably predict reaction rates from first principles for higher energies. Therefore, it is important to test the extrapolations and optimize model parameters for the new energy regime at the LHC. The b-hadrons from proton-proton collisions are a major source of background in searches for the Higgs boson and other heavy not-yet-discovered particles. Hence, it is important to quantify their presence in different reactions for the main research program at the LHC. The measurement of the Bs-meson production cross section presented in this dissertation complements the measurements for the B+ and the Bd mesons. The outcome is compared to different models for quark production and hadronization. The three CMS measurement of B-meson production cross sections are used to calculate the Bs to J/psi phi branching fraction. The measurement of the time-dependent decay rate of Bs mesons probes the weak interaction and includes the possibility to observe sizable particle anti-particle asymmetries caused by heavy particles and new forces between them that are not predicted by the Standard Model. In this dissertation the lifetime, lifetime difference, and CP-composition in the decay Bs to J/psi phi have been extracted with a Maximum Likelihood fit. The J/psi meson decays into two muons, while the phi meson into two charged kaons. The results are presented for the data recorded during the year 2010 with the Compact Muon Solenoid. It is a general-purpose particle detector centered at one of the interaction points of the Large Hadron Collider, a proton-proton collider located at the particle physics laboratory CERN in Geneva (Switzerland). It is designed to explore a wide range of physics in proton-proton collisions. The investigations presented here assess and benchmark the performance of a variety of detector components including track and muon reconstruction. For reconstruction of long-lived particles, such as the b-hadrons, the silicon pixel detector provides the most signicant information.

Analysis of the Ultra-peripheral Events in Heavy-ion Collisions in the CMS Experiment at the Large Hadron Collider

Analysis of the Ultra-peripheral Events in Heavy-ion Collisions in the CMS Experiment at the Large Hadron Collider
Author: Marek Walczak (fizyka)
Publisher:
Total Pages:
Release: 2021
Genre:
ISBN:

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Dotyczy: nuclear parton distribution functions, photoproduction, QCD, heavy-ion collisions, CMS, ultra-peripheral collisions, jądrowe rozkłady partonów, fotoprodukcja, QCD, zderzenie ciężkich jonów, CMS, zderzenia ultraperyferyczne.

Measurement of [phi] Meson Production in Cu+Cu Collisions at 200 GeV Using the PHOBOS Detector at RHIC

Measurement of [phi] Meson Production in Cu+Cu Collisions at 200 GeV Using the PHOBOS Detector at RHIC
Author: Siarhei S. Vaurynovich
Publisher:
Total Pages: 275
Release: 2012
Genre:
ISBN:

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Strong enhancement of production of strange particles, and in particular of [phi] mesons, in heavy ion collisions of sufficiently high energies has been predicted to be an indication of a formation of a new state of matter, composed of deconfined quarks and gluons and having a property of chiral symmetry, called Quark Gluon Plasma (QGP). Studying production of [phi] mesons is of special interest due to their small cross-section of interaction with non-strange hadrons and due to their long lifetime, which should allow [phi] mesons to decouple from the strongly interacting medium produced in heavy ion collisions early in time and to escape the medium before decaying, thereby preserving information about the conditions in which the mesons were produced. In addition, the decay properties of [phi] mesons have been predicted to be modified in a hadronic gas medium. The [phi] -> K+K~ decay is of particular interest since the mass of a [phi] meson in vacuum is very close to the mass of two charged kaons, and consequently, even a small change in the mass or the width of [phi] mesons or in the mass of kaons would have a strong effect on the decay properties. Measurement of [phi] meson production using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC) has proven to be especially challenging due to a small acceptance of the PHOBOS spectrometer and due to a much lower than predicted yield of [phi] mesons in heavy ion collisions at the highest RHIC energy. The measurement required a development of a new tracking algorithm, specifically tailored to reconstruct charged kaons with a high efficiency in a high hit density environment, keeping at the same time the necessary computing time within feasible limits. Results of a measurement of [phi] meson invariant yield in the rapidity interval 0 y