Browsing by Subject "STAR"

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A large area time of flight detector for the STAR experiment at RHIC
(2009-12) Kajimoto, Kohei; Hoffmann, Gerald W.
A large area time of flight (TOF) detector based on multi-gap resistive plate chamber (MRPC) technology has been developed for the STAR (Solenoidal Tracker at RHIC) experiment at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory, New York. The TOF detector replaces STAR's Central Trigger Barrel detector with 120 trays, each with 32 MRPCs. Each MRPC has 6 channels. The TOF detector improves by a factor of about 2 STAR's particle identification reach in transverse momenta and enhances STARs physics research program.
Two-particle correlations in angular and momentum space in heavy ion collisions at STAR
(2013-05) Oldag, Elizabeth Wingfield; Hoffmann, Gerald W.
For over a decade studies of the strong interaction in extremely dense nuclear environments have been done at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. It is hypothesized that colliding two beams of Au nuclei at relativistic speeds creates an environment of hot dense nuclear matter where the quarks and gluons inside the nucleus, which are normally confined within the protons and neutrons, become deconfined into a soup called the quark-gluon plasma. Since direct observation of this short-lived phase is impossible, many sophisticated analysis techniques attempt to study the early interactions via the final state particles. What has emerged from analyses of the data are two, contradictory paradigms for understanding the results. On the one hand the colliding quarks and gluons are thought to strongly interact and reach thermal equilibrium. The other view is that primary parton-parton scattering leads directly to jet fragmentation with little effect from re-scattering. It is in principle possible to distinguish and perhaps falsify one or both of these models of relativistic heavy ion collisions via the analysis of two-particle correlations among all charged particles produced in [mathematical symbols] = 200 GeV Au+Au collisions at the STAR experiment at RHIC. This dissertation presents studies of two-particle correlations, whose derivation can be traced back to Pearson's correlation coefficient, in transverse momentum and angular space. In momentum space a broad peak is observed extending from 0.5-4.0 GeV/c which, as a function of nuclear overlap, remains at a fixed position while monotonically increasing in amplitude. Comparisons to theoretical models suggests this peak is from jet fragmentation. In a complementary study the momentum distribution of correlations in ([eta],[phi]) space is investigated. The momentum distribution of correlated pairs that contribute to the peak near the origin, commonly associated with jet fragmentation, is peaked around 1.5 GeV/c and does not soften with increased centrality. These measurements present important aspects of the available six dimensional correlation space and provide definitive tests for theoretical models. Preliminary findings do not appear to support the hypothesis of a strongly interacting QGP where back-to-back jets are expected to be significantly suppressed.
Two-particle correlations of identified particles in heavy ion collisions at STAR
(2016-08) Bhattarai, Prabhat; Markert, Christina; Ray, Robert L. (Robert Landon); Bohm, Arno; Walker, Stephen; Onyisi, Peter
The study of quarks and their interactions through gluons has been an active area of research since their discovery. For two decades the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been dedicated to studying the interactions between quarks by producing nuclear matter in an extremely dense and hot environment. It has been hypothesized that colliding beams of atomic nuclei near the speed of light creates the hot and dense environment in which all quarks in the nuclei de-confine to form a short-lived state of matter called a Quark Gluon Plasma (QGP). Because of the short lifetime of QGP, it is impossible to observe it directly and, the only way to study such matter is through the final state particles. Two-particle correlation, which is defined using Pearson's normalized covariance, is one of the techniques to study the early interactions via the final state particles. A broad survey has been made to study the two-particle correlations of identified-charged hadrons (pi, K and p) in various ranges of momentum for the hadrons produced in √sNN=200 GeV Au+Au collisions at the STAR experiment at RHIC. A total of 2123 two-dimensional independent structures made by correlation coefficients in relative angular space in (eta, phi) for different combinations of identified hadrons have been studied. Correlations between any two identified particles contrasts to all-particle correlations giving an opportunity to study the contribution of each particle species in the hadronization processes. As a new feature, same-side anti-correlations are observed in both like-sign and unlike-sign pairs in certain yT bins and in certain identified particles. A significant feature of the final state distribution of particles is an azimuthal anisotropy which is defined as the second Fourier component; the amplitude is proportional to parameter v2. We report the measure of azimuthal anisotropy of identified hadrons for the first time and test for the factorization used in conventional analysis. The data presented here constitute a comprehensive measurement of the light-flavor, di-hadron density as function of collision centrality, transverse momentum and 2D relative angles in longitudinal (beam direction) and azimuthal directions.