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Understanding the spin structure of the nucleon can be considered as one of the fundamental goals in nuclear physics. Following the introduction of the quark model in 1964, the spin of the proton was naively explained by the alignment of spins of the valence quarks. However, in our current understanding, the valence quarks, sea quarks, gluons, and their possible orbital angular momentum are all expected to contribute to the overall spin of the proton. Despite this significant progress, our understanding of the individual spin contributions of quarks and antiquarks to the proton is not yet complete. Measurements of W± single spin asymmetries in longitudinally polarized proton-proton collisions at RHIC provides unique and clean access to the individual helicity distributions of light quarks and antiquarks of the proton. W± boson are produced through the annihilation of up + anti-down (anti-up + down) quarks and can be detected through their leptonic decays to electrons and anti-electron neutrinos (positrons and electron neutrinos). Due to maximal violation of parity during the production, W bosons couple to left-handed quarks and right-handed anti-quarks and hence offer direct probes of their respective helicity distributions in the nucleon. The STAR experiment at RHIC is well equipped to measure W decay electrons and positrons in longitudinally polarized p+p collisions, where only the charged lepton is observed in the final state with a large missing transverse energy opposite in azimuth due to the undetected neutrino. In this dissertation, the details of the analysis and the results of the longitudinal single spin asymmetry, AL, for W boson production at RHIC are presented. The total integrated luminosity of the data analyzed is 246 pb-1 with an average beam polarization of ~54%. The data are collected during 2013 in longitudinally polarized proton-proton collisions at √S =510 GeV by the STAR experiment at RHIC. The analysis includes the procedure, the results and the evaluation of the systematic uncertainty of the calibration of the STAR Barrel Electromagnetic Calorimeter which was performed coincident with the primary W AL analysis. The W AL analysis is discussed in terms of data QA, the reconstruction of W bosons via decayed electrons and positrons, and the estimation of the electroweak and QCD type background contributions. The reconstruction of W decay events includes the use of the Time Projection Chamber for the tracking purposes and the Barrel Electromagnetic Calorimeter for the identification and isolation of electron and poistron candidates by measuring their transverse energies in the calorimeter towers. Finally the results of AL for W+ (W-) are reported as a function of decay positron (electron) pseudo-rapidity, η, between -1 and +1. The theoretical predictions for the spin asymmetries calculated using recent polarized and unpolarized parton distribution functions, are compared with the measured values. / Physics

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24585号 / 工博第5091号 / 新制||工||1975(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 関 修平, 教授 梶 弘典, 教授 SIVANIAH Easan / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir die opsomming

<p>Heavy flavor hadrons serve as valuable probes of the transport properties of the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. In this dissertation, we introduce a comprehensive framework that describes the full-time evolution of heavy flavor in heavy-ion collisions, including its initial production, in-medium evolution inside the QGP matter, hadronization process from heavy quarks to their respective mesonic bound states and the subsequent interactions between heavy mesons and the hadron gas.</p><p>The in-medium energy loss of heavy quarks is studied within the framework of a Langevin equation coupled to hydrodynamic models that simulate the space-time evolution of the hot and dense QGP matter. We improve the classical Langevin approach such that, apart from quasi-elastic scatterings between heavy quarks and the medium background, radiative energy loss is incorporated as well by treating gluon radiation as a recoil force term. The subsequent hadronization of emitted heavy quarks is simulated via a hybrid fragmentation plus recombination model. The propagation of produced heavy mesons in the hadronic phase is described using the ultra-relativistic quantum molecular dynamics (UrQMD) model. Our calculation shows that while collisional energy loss dominates the heavy quark motion inside the QGP in the low transverse momentum (pT) regime, contributions from gluon radiation are found to be significant at high pT. The recombination mechanism is important for the heavy flavor meson production at intermediate energies. The hadronic final state interactions further enhance the suppression and the collective flow of heavy mesons we observe. Within our newly developed framework, we present numerical results for the nuclear modification and the elliptic flow of D mesons, which are consistent with measurements at both the CERN Large Hadron Collider (LHC) and the BNL Relativistic Heavy-Ion Collider (RHIC); predictions for B mesons are also provided.</p><p>In addition, various transport properties of heavy quarks are investigated within our numerical framework, such as the thermalization process of heavy quarks inside the QGP, and how the initial configuration of the QGP as well as its properties affect the final state spectra and the elliptic flow of heavy mesons and their decay electrons. The effects of initial state fluctuations in heavy-ion collisions are also studied and found to enhance the heavy quark energy loss in a (2+1)-dimensional boost invariant scenario. Furthermore, a new set of observables -- heavy-flavor-tagged angular correlation functions -- are explored and found to be potential candidates for distinguishing different energy loss mechanisms of heavy quarks inside the QGP.</p> / Dissertation

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