Browsing by Author "Zhou, Jianhang"

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    Construction of a new detector, and calibration strategies, for start timing in the STAR experiment at RHIC
    (2007) Zhou, Jianhang; Roberts, Jabus B.
    The Time of Flight (TOF) system of the Solenoidal Tracker at RHIC (STAR) at the Relativistic Heavy Ion Collider (RHIC) consists of two different subsystems: the start detector and the stop detector. Described in this thesis is the design, construc tion, and operation of a new start detector for STAR. This new start detector, called the Upgraded Pseudo Vertex Position Detector (upVPD) provides many improvements to the old start detector, called the Pseudo Vertex Position Detector (pVPD). The upVPD is expected to have better efficiency per event and better start timing and primary vertex location resolution compared to the pVPD, which will improve the performance of the STAR TOF and STAR Trigger systems. Timing offsets and the slewing effect smear the raw data read-out by the detectors and require offline calibration. The general approach and a few possible algorithms for such calibrations are also described. The analysis results from both the pVPD and the upVPD detectors are presented. Additional cosmic ray tests of the upVPD detectors were also performed, and the calibration results from these data are also discussed.
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    Light (anti-)nuclei production in the STAR experiment at RHIC
    (2009) Zhou, Jianhang; Roberts, Jabus B.
    Presented in this thesis is the study of light (anti-)nuclei production in ultra-relativistic heavy ion collisions. In these collisions hot dense matter is created, in which the quarks and gluons are deconfined. As this hot dense matter expands and cools down, quarks recombine together to form new hadrons. At the final stage called thermal freeze-out, nucleons can combine into light nuclei. Therefore the study of light nuclei production provides a probe for understanding the physical properties of the expanding system at the thermal freeze-out, such as the temperature and the eccentricity. In this thesis, the transverse momentum ( p T ) spectra, and the elliptic flow ( v 2 ) of the anti-deuteron, and the coalescence parameters B 2 for d, d and B 3 for 3 He, from STAR Run-V Cu+Cu 200 GeV collisions are studied and compared with STAR Run-VI Au+Au 200 GeV results. Based on the Au+Au collision results, a blast-wave (BW) model is used to fit the transverse momentum spectra and elliptic flow of hadrons. These fit parameters are used in the BW model to predict the deuteron and helium production. The comparison between the BW predicted and the experimentally measured results leads to a consistent understanding of the freeze-out features. Also presented in the thesis is the search for the anti-alpha particle ( 4 He), which has never been discovered before. The search for heavier anti-nuclei is interesting as they are predicted by the theory but hard to find in real world. The anti-deuteron was discovered many years ago and 3 He was found recently. The anti-alpha particles, if confirmed, will be the heaviest anti particles ever found. In this thesis two anti-alpha candidates are shown. Both are found in STAR Run-VII Au+Au collisions. With the accumulated events and the new particle identification method in the future runs, there is hope to find and confirm more candidates.