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Measurement of charmed meson azimuthal anisotropy in Au+Au collisions at a center of mass energy of 200 GeV per nucleon pair at RHIC

Lomnitz, Michael Richard
http://rave.ohiolink.edu/etdc/view?acc_num=kent1478709564749636

Abstract Details

2016, PHD, Kent State University, College of Arts and Sciences / Department of Physics.
Heavy ion collisions at RHIC provide a unique environment to probe into the understanding of nuclear matter under extreme high temperature and density conditions. Among the many insights that can be provided is the further understanding of the QCD (Quantum Chromo Dynamics) phase diagram and equation of state, as well as search for evidence of the QCD critical point and chiral symmetry restoration. Production of heavy quarks in high-energy nuclear collisions at RHIC occurs mainly through gluon fusion and quark anti-quark annihilation; and while heavy flavor production may be somewhat enhanced due to final state interactions via thermal processes these channels are greatly suppressed due to the heavy quark masses. Thus heavy flavor provides an ideal probe in the study of the hot and dense medium created in high-energy collisions as it is produced early in the evolution of the collision, and hence is sensitive to the collision dynamics of the partonic matter at early stages. Previous measurements of collective motion (flow) in light quarks (u,d,s) at RHIC suggest that partonic collectivity has been achieved in the collisions. These results also seem to suggest that the dense matter produced during collisions thermalizes at very high temperatures and form a strongly coupled Quark Gluon Plasma (QGP) whose behavior is compatible with viscous hydrodynamic models with a low shear-viscosity-to-entropy-density (η/s) ratio. The question remains as to whether or not this collective behavior applies to heavy flavor and a detailed description of the behavior of heavy flavor is essential to understand the underlying dynamics, distinguish between different energy loss mechanisms, and constrain theoretical models. In particular, if the elliptic flow of charm quarks is found to be comparable to that of lighter matter this would be indicative of frequent interactions between all quarks and would strongly support the discovery of QGP at RHIC. Understanding how this collective behavior emerges from the individual interactions between partonic matter as well as the differences between quarks species will need to be investigated further to understand this new state of matter and is at the center of the RHIC scientific program. However, precise measurements of open heavy flavor are difficult to obtain due to the low yields and short lifespan of heavy hadrons. One approach to reduce this combinatorial background and reconstruct open heavy flavor in heavy ion collisions involves distinguishing between an event's primary vertex and a hadron's decay vertex through direct topological reconstruction from the decay products. The Heavy Flavor Tracker (HFT) silicon vertex upgrade for the STAR experiment, which made its debut during the 2014 year's run together with the Muon Telescope Detector (MTD), has vastly improved the experiment's heavy flavor capabilities making STAR an ideal detector to study the hot and dense matter created in heavy ion collisions. Taking advantage of the greatly improved pointing resolution from a dedicated micro-vertex detector, it is possible to directly track and reconstruct weak decay products from hadrons comprised of heavy ``charm" and ``bottom" quarks. The HFT consists of three sub-detectors: PIXEL (PXL), the Intermediate Silicon Tracker (IST) and the Silicon Strip Detector (SSD) with 4 separate layers of silicon to guide tracks reconstructed in the Time Projection Chamber down to a pointing resolution of around 30 \mum for one GeV/c pions, a requirement to distinguish between an event's primary vertex and the position of a hadron's decay. This dissertation is centered on using the HFT to reconstruct charmed mesons in Au+Au collisions at a center of mass energy of 200 GeV per nucleon through their hadronic channels (D+/-→K-/+2π+/-, D0→K-π+). In order to achieve the precision of the HFT for physics analysis, careful calibration of the detector is essential to ensure the quality of the processed data and, as a consequence, any measured observables. As such, details related to the identification of bad channels in the PXL subsystem as well as the internal alignment of the HFT detector are presented in this dissertation. In-depth studies of the detector's response were performed in simulations and, together with comparisons to data, were used to verify our understanding of the detector's delivered efficiency and tracking performance. As motivated above, a sizable sample of charmed meson candidates was obtained and used to study the flow patterns employing the event plane method, whose simple interpretation allows for immediate comparison to theoretical models. The thesis presents the first measurement of D-meson v2 and v3 at RHIC energy, and the result shows D-meson v2 is finite indicating charm quarks are participating the collective behavior with the medium. The results are compared to lighter particle species and appear to follow the same Number of Constituent Quarks (NCQ) scaling as is observed for other hadrons. The measured v3 is found to be non-zero within large uncertainties, indicating the importance of considering fluctuations in the initial conditions of the collision. These results are then compared to a series of model calculations in an attempt to extract information related to the transport properties of the bulk matter formed in the collision. In particular, the measured elliptic flow for D0 is found to favor a scenario where charm quarks flow with the medium and compatible with a (3+1)D viscous hydrodynamics. The comparisons were used to extract a range of compatible values for the charm spatial diffusion coefficient 2πTDs in the QGP medium. Once processed, the dataset collected in 2016 (~2 billion MinBias events) will provide a further factor 2-4 in the D0 significance. This dataset will allow STAR to study the centrality dependence of charm hadron v2 in more detail as well as the production of open bottom at RHIC in order to further constrain the transport properties of the medium.
Margetis Spyridon, Prof. (Advisor)
Xin Dong, Dr. (Advisor)
189 p.
Nuclear Physics; Physics
Nuclear Physics; Heavy Ion Collisions; Quark Gluon Plasma; Heavy Flavor; RHIC

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Citations

  • Lomnitz, M. R. (2016). Measurement of charmed meson azimuthal anisotropy in Au+Au collisions at a center of mass energy of 200 GeV per nucleon pair at RHIC [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1478709564749636

    APA Style (7th edition)

  • Lomnitz, Michael. Measurement of charmed meson azimuthal anisotropy in Au+Au collisions at a center of mass energy of 200 GeV per nucleon pair at RHIC. 2016. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1478709564749636.

    MLA Style (8th edition)

  • Lomnitz, Michael. "Measurement of charmed meson azimuthal anisotropy in Au+Au collisions at a center of mass energy of 200 GeV per nucleon pair at RHIC." Doctoral dissertation, Kent State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1478709564749636

    Chicago Manual of Style (17th edition)

kent1478709564749636
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This open access ETD is published by Kent State University and OhioLINK.