title: phi meson production at forward rapidity in Au+Au collisions at sqrt(s_NN)= 200GeV.
Creators: name: Acharya, Uttam
Publisher: name: Georgia State University
Year: 2026

description: <p>Given its strange quark contents (ss), the ? - meson serves as an excellent probe for examining the hot and dense state of nuclear matter, known as the quark-gluon plasma (QGP), produced in high-energy heavy-ion collisions, such as those occurring at The Relativistic Heavy Ion Collider (RHIC). The strangeness enhancement in medium was believed to be a key signature probe of QGP. In a plasma, strange and anti-strange quarks are mainly generated through gluon-gluon interactions, which happen very quickly, bringing the strange quark abundance close to equilibrium. When hadronization occurs, the s and s quarks from the plasma are highly likely to combine and form ?-mesons. The ? ? ?+?? decay channel is particularly valuable for studying nuclear matter effects on ? - meson production due to the minimal interaction between muons and the surrounding hot hadronic matter.</p>
<p>The PHENIX experiment, at RHIC, has conducted measurements on ? - meson production and nuclear modification in asymmetric small collisions system like d + Au and Cu + Au at a center-of-mass energy of 200 GeV. While in d + Au measurements, broadening in the intermediate pT was observed at Au-going (backward) direction (?2.2 < y < ?1.2) which is a typical behavior of Cronin effect, a cold nuclear matter effect (CNM) existing in medium, the Cu + Au measurement offer a unique approach to understanding the interplay between hot and cold nuclear matter effects. However, the challenging environment created by the large combinatorial background at forward and backward rapidities in heavy-ion collisions has limited previous measurements at RHIC to smaller collision species.</p>
<p>To gain a deeper understanding of the cold and hot nuclear matter effects and investigate the properties of the Quark-Gluon plasma (QGP), RHIC has collided gold-gold (Au+Au) collisions in 2014, producing events huge enough to ever recorded by the PHENIX detector, aimed at elucidating the characteristics of QGP and the intricacies of the strong force. Due to the high multiplicity events, it is expected in heavy ion collisions that we need to deal with the challenges arising from enormous backgrounds. So, it is crucial to utilize a proper background estimation method and proper analysis approach such that proper signal can be extracted for the measurement. Also the measurement at the forward rapidity region with very low branching ratio for ? - meson to decay into muons makes it further challenging to use a traditional way to obtain the signal with proper background estimate.</p>
<p>This thesis outlines a methodology for modeling and eliminating backgrounds, presenting the ? - meson measurement at forward and backward rapidities in heavy-ion collisions at RHIC using the Forward Silicon Vertex(FVTX) detector in PHENIX in Au+Au collisions. The ? - meson invariant yields and nuclear modification factors RAA are reported as functions of the number of participating nucleons, rapidity, and transverse momentum within the kinematic range of 1.2 < |y| < 2.2 and 2.50 < p<sub>T </sub>< 5.0 GeV/C. While the theoretical model prediction is yet to be performed, the results presented in this thesis may offers a way to gain insights into the combination of hot nuclear matter (HNM) and cold nuclear matter (CNM) effects on ? - meson production in heavy-ion collisions, contributing to the understanding of the quark-gluon plasma. While we do access CNM and HNM effect in Au + Au collision, the objective is to study the HNM.</p>