Measurement Of Multijet Production In Ep Collisions At High Q 2 And Determination Of The Strong Coupling S Alpha S

Author : Yue Liang
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (14 download)

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Download or read book D0-Meson Elliptic, Triangular Flows And Event-Shape-Engineering Study In Au+Au Collisions At [square Root]S[subscript](NN) written by Yue Liang and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Heavy ion collisions at Relativistic Heavy Ion Collider (RHIC) provide a unique environment to probe nuclear matter under extremely high temperature and density conditions. Among the many insights that can be provided are studying the Quark Gluon Plasma (QGP) created in these collisions, the interaction of color-charged probes with the QGP, the mechanism of hadronization as well as the nature of phase transition to the deconfined phase. Production of heavy quarks in high-energy nuclear collisions occurs mainly through initial hard scattering, via gluon fusion and quark anti-quark annihilation, since the thermal production in the hot QCD medium is significantly suppressed due to the heavy quark masses. This makes heavy quarks ideal probes of the QGP as they experience the whole medium evolution. The diffusion of a heavy particle through a heat bath of the hot-QCD medium can be quantified by the spatial diffusion coefficient D[subscript]s, in analogy to the Brownian motion in molecular physics. Early calculations based on perturbative methods for the diffusion coefficient for the charm and bottom quarks in a QGP produced values of D[subscript]s(2[pi]T) ~ 30 ~ O(1/[alpha]2[subscript]s) for a strong coupling constant of [alpha][subscript]s ~ 0.3-0.4 and with a value varying only weakly with temperature. We now know that these values for D[subscript]s are too large to account for the open heavy-flavor (HF) observables, including the elliptic flow (v2) of D0 mesons, in heavy-ion collisions at RHIC and the LHC. New measurements, including of higher order flow, with better precision and studying their dependence on collision geometry and size and shape of the produced medium allow us to better constrain the value of D[subscript]s and the heavy quark interaction with the QGP. The Solenoidal Tracker At RHIC (STAR) experiment is one of the two remaining large detector systems at the RHIC. The Time Projection Chamber (TPC) is the main detector at STAR measuring 4.2 m in length and 4 m in diameter, it provides full azimuthal coverage out to ± 1.0 units of rapidity and particle identification down to transverse momenta of 100 MeV/c. The Heavy Flavor Tracker (HFT) silicon vertex upgrade for the STAR experiment, is utilizing active pixel sensors and silicon strip technology and provides excellent track pointing resolution to allow the reconstruction of heavy flavor hadron decays. My thesis work is utilizing the STAR Heavy Flavor Tracker's combined datasets recorded during RHIC 2014 and 2016 runs to measure with improved precision the D0-meson elliptical (v2) and triangular flow (v3) as a function of event centrality (quantity which describes the overlap region between the two colliding nuclei) and D0 transverse momentum. I also present results obtained with a new method of event-shape-engineering (ESE) to study correlations of D0 v2 with the event geometry. The physics results are compared with model simulations. My results confirm that the D0 v2 follows the same number-of-constituent-quark (NCQ) scaling as light flavor hadrons. Non-zero v3 is observed, and by combining the 2014 and 2016 data, I also observe that the v3 also follows the NCQ scaling as light hadrons. Compared to theoretical model calculations, the observed large v2/v3 results demonstrate that charm quarks gain these strong collectivity through the diffusion in the strongly-coupled QGP medium. From the ESE study, I observe that the event-shape q2 dependence of the measured [pi][superscript]±, K[superscript]± and D0 hadrons follow the similar linear dependence with comparable slope in 10-40% Au+Au collisions. This demonstrated that the heavy flavor hadron v2 is driven by the event geometry. These results allow putting strict constraints on the values of the diffusion coefficient D[subscript]s. STAR's v2 results have been included in recent model analyses and provided a constraint on the 2[pi]TD[subscript]s to be around 2-5 near the T[subscript]c region while the temperature dependence from various models remains largely uncertain. The next phase of heavy flavor programs at RHIC and LHC need to focus on better constraining the temperature/momentum dependence on the heavy quark diffusion coefficient. Furthermore, since the bottom quark mass is much larger than that of charm, theoretically, bottom quark transport in QGP medium can be better described by the Langevin simulation. Testing the universality of heavy quark spatial diffusion coefficient between charm and bottom quarks will be also the next focus in RHIC and LHC HF programs.