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Thesis (Ph. D.)--Ohio State University, 2002. / Title from first page of PDF file. Document formatted into pages; contains xx, 143 p.; also contains graphics. Includes abstract and vita. Advisor: L. Stanley Durkin, Dept. of Physics. Includes bibliographical references (p. 137-143).

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Le plasma de quarks et de gluons (QGP) est un état de la matière nucléaire apparaissant à hautedensité d’énergie. En laboratoire, il est possible de reproduire de telles conditions grâce aux collisionsd’ions lourds aux énergies ultra-relativistes. ALICE (A Large Ion Collider Experiment) estl’expérience du LHC dédiée à la mise en évidence du QGP.Différentes signatures ont été proposées et étudiées expérimentalement comme manifestations duQGP. Parmi celles-ci, le méson J/ψ joue un rôle central. Il fait partie de la famille des quarkonia,états mésoniques (Q¯Q) formées d’un quark lourd c ou b et de son anti-quark, liés par un potentield’interaction forte. En 1986, Matsui et Satz proposèrent la suppression des charmonia (états liés cc)et notamment du J/ψ comme signature de la formation du plasma de quarks et de gluons.ALICE peut détecter le J/ψ à grande rapidité (2.5 < y < 4) via le canal de désintégration en deuxmuons. Cette thèse porte sur la mesure de la production du J/ψ, via le canal muonique, dans lescollisions pp à une énergie dans le centre de masse de 2.76 et 7 TeV. Elle a exploité les donnéesacquises en 2010 et 2011 auprès du collisionneur LHC.Tenter d’appréhender le mécanisme de production du J/ψ (et plus généralement du quarkonium)dans les collisions pp est un préalable nécessaire avant d’aborder le degré de complexité suivantque constitue le cas des collisions noyau-noyau. Il est également un test important pour la QuantumChromo Dynamics (QCD), la théorie de l’interaction forte, aux énergies très élevées du LHC. / Quarkonia are meson states whose constituents are a charm or bottom quark and its correspondingantiquark (Q¯Q). The study of the production of such bound states in high-energy hadron collisionsrepresents an important test for the Quantum Chromo-Dynamics. Despite the fact that the quarkoniumsaga has already a 40-year history, the quarkonium production mechanism is still an open issue.Therefore, measurements at the new CERN Large Hadron Collider (LHC) energy regimes are extremelyinteresting.In this thesis, the study of inclusive J/ψ production in proton-proton (pp) collisions at √s = 2.76and 7 TeV, obtained with the ALICE experiment, is presented. J/ψ mesons are measured at forwardrapidity (2.5 < y < 4), down to zero pT, via their decay into muon pairs (μ+μ−).Quarkonium resonances also play an important role in probing the properties of the stronglyinteracting hadronic matter created, at high energy densities, in heavy-ion collisions. Under suchextreme conditions, the created system, according to QCD, undergoes a phase transition from ordinaryhadronic matter to a new state of deconfined quarks and gluons, called Quark Gluon Plasma(QGP). The ALICE experiment at CERN LHC has been specifically designed to study this state ofmatter. Quarkonia, among other probes, represents one of the most promising tools to prove the QGPformation. In order to correctly interpret the measurements of quarkonium production in heavy-ioncollisions, a solid baseline is provided by the analogous results obtained in pp collisions.Hence, the work discussed in this thesis, concerning the inclusive J/ψ production in pp collisions,also provides the necessary reference for the corresponding measurements performed in Pb-Pb collisionswhich were collected, by the ALICE experiment, at the very same center-of-mass energy pernucleon pair (√sNN = 2.76 TeV).

A measurement of J/\Psi polarization has been performed for 200 GeV proton+proton collisions with the PHENIX Muon Arms at RHIC. The results from the current data show no polarization within the PHENIX acceptance range. The results are consistent with the current model predictions and other experimental measurements.

Over the last few decades, the Standard Model (SM) of particle physics has been used as a means of understanding the world around us. However, there is an increasing amount of data that suggests the SM of particle physics only describes nature up to energies of the electroweak scale. Extensions to the SM have been developed as a means of explaining experimental observation. If these extensions are indeed the correct mathematical descriptions of nature, the Large Hadron Collider (LHC), located at the European Center for Nuclear Research (CERN) near Geneva, Switzerland, is expected to produce new and exciting physics signatures that can shed light on the evolution of our universe since the early hypothesized Big Bang. Of particular interest are models that may lead to events with highly energetic tau lepton pairs. In this dissertation, focus is placed on a possible search for new heavy gauge bosons decaying to highly energetic tau pairs using a data sample corresponding to an integrated luminosity of 36 pb^-1 of proton-proton collisions at sqrt(s) = 7 TeV collected with the CMS detector at the CERN LHC. The number of observed events in the data is in good agreement with the predictions for SM background processes. In the context of the Sequential SM, a Z0 with mass less than 468 GeV/c^2 is excluded at 95 percent credibility level, exceeding the sensitivity by the Tevatron experiments at the Fermi National Accelerator Laboratory.

In this thesis a production of J/ψ meson in pp and heavy-ion collisions was investigated. A comparison between Monte Carlo generator and data by ATLAS experiment at CERN was done. PYTHIA version 8.2 was chosen for the Monte Carlo generator. In the first part, comparisons of several configurations of PYTHIA were used to establish the best matching of the Monte Carlo to the data using collisions with centre-of-mass energy of 7 TeV. Choice of parton distribution functions was found not to be important, while presence or absence of initial and final state radiation were proven to have an important impact on the result. In the second part, correlation of J/ψ meson and the jet production was quantified. Anti-kt algorithm with R = 0.4 was used to reconstruct jets. Pairs of muons were used to identify J/ψ meson candidates. Only less than 10% of J/ψ mesons were found to be associated with jets. 1

Longstanding evidence from observational astronomy indicates that non-luminous "dark matter" constitutes the majority of all matter in the universe, yet this mysterious form of matter continues to elude experimental detection. This dissertation presents a search for dark matter at the Large Hadron Collider using 139 fb\(^{-1}\) of proton-proton collision data at a centre-of-mass energy of \(\sqrt{s} = 13\,\)TeV, recorded with the ATLAS detector from 2015 to 2018. The search targets a final state topology in which dark matter is produced from the proton-proton collisions in association with a pair of W bosons, one of which decays to a pair of quarks and the other to a lepton-neutrino pair. The dark matter is expected to pass invisibly through the detector, resulting in an imbalance of momentum in the plane transverse to the beam line. The search is optimized to test the Dark Higgs model, which predicts a signature of dark matter production in association with the emission of a hypothesized new particle referred to as the Dark Higgs boson. The Dark Higgs boson is predicted to decay to a W boson pair via a small mixing with the Standard Model Higgs boson discovered in 2012. Collisions that exhibit the targeted final state topology are selected for the search, and an approximate mass of the hypothetical Dark Higgs boson is reconstructed from the particles in each collision. A search is performed by looking for a deviation between distributions of the reconstructed Dark Higgs boson masses and Standard Model predictions for the selected collisions. The data is found to be consistent with the Standard Model prediction, and the results are used to constrain the parameters of the Dark Higgs model. This search complements and extends the reach of existing searches for the Dark Higgs model by the ATLAS and CMS collaborations. / Graduate

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The goal of this project was to develop a lightweight Monte-Carlo (MC) event generator for hyperon pair production in antiproton-proton collisions, and demonstrate it in one of the hyperon decay reaction channels, which is collisions of proton and antiproton to lambda hyperon and anti-lambda hyperon, and they decay to antiproton-positive pion pair, and proton-negative pion pair. The prototype of this external MC event generator we presented here is based on the software framework of ROOT. Compared to the corresponding framework of embedded MC event generators that is currently used in the PANDA experiment at FAIR, PandaRoot, it allows for easier and quicker testing of new models or formalisms on synthetic data, for example for studying spin observables like polarisation. The event generator was benchmarked by studying angular distributions in final states, which are constructed by kinematic relations of 4-momentum vectors in different reference frames for all mother and daughter particles.