Browsing by Author "Bhattarai, Prabhat"
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Item Monte Carlo glauber model : quadrupole correlations in Au+Au collisions(2015-12) Bhattarai, Prabhat; Walker, Stephen G., 1945-; Ray, Robert L. (Robert Landon)The study of quarks and their interaction through gluons has been active area of research since its discovery. It has been about two decades that Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is dedicated to study interaction between quarks by producing nuclear matter in extremely dense and hot environment. It has been understood that colliding beams of atomic nuclei at a speed close to 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 Quark Gluon Plasma (QGP). Because of the short lifetime of QGP, the only way to study such matter is through the final state of particles. A significant feature of the final state distribution of particles is an azimuthal anisotropy, which is dominated by the second Fourier component; the amplitude is proportional to parameter v2. One of the major interpretations of this anisotropy is based on the hypothesized thermal equilibrium of the QGP leading to pressure driven collective flow. The other is that quantum interference among many quark and gluon scatterings leads directly to anisotropy in the final state. The present report presents a way to calculate the observed quadrupole correlation amplitude, v2, without assuming collective flow. The study uses a Monte Carlo method to simulate the gold-gold nuclear collision data using experimental results from proton-proton collisions. The quality of simulated results is assured by comparison to theoretical understanding of the phenomenon as well as to the experimental data. This report presents studies of two-particle correlations, whose derivation can be traced back to Pearson's correlation coefficient, in azimuthal angular space of the simulated tracks of the particles produced in the gold-gold of collisions. The correlation result is fitted to extract the v2 and compared to the same quantity from the experimental data. The comparison suggests that a fraction of the v2 in gold-gold collisions can be accounted for by phenomenon not associated with collective flow.Item 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, PeterThe 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.