Abstract
Azimuthal correlations of charged hadrons with direct-photon ($\gamma_{dir}$) and neutral-pion ($\pi^{0}$) trigger particles are analyzed in central Au+Au and minimum-bias $p+p$ collisions at $\sqrt{s_{_{NN}}} = 200$ GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity from central Au+Au collisions are compared with $p+p$ collisions to quantify the suppression in Au+Au collisions. The suppression of the away-side associated-particle yields per $\gamma_{dir}$ trigger is independent of the transverse momentum of the trigger particle ($p_{T}^{\mathrm{trig}}$), whereas the suppression is smaller at low transverse momentum of the associated charged hadrons ($p_{T}^{\mathrm{assoc}}$). Within uncertainty, similar levels of suppression are observed for $\gamma_{dir}$ and $\pi^{0}$ triggers as a function of $z_{T}$ ($\equiv p_T^{\mathrm{assoc}}/p_T^{\mathrm{trig}}$). The results are compared with energy-loss-inspired theoretical model predictions. Our studies support previous conclusions that the lost energy reappears predominantly at low transverse momentum, regardless of the trigger energy.
Highlights
Over the past decade, experiments at the Relativistic Heavy IonCollider (RHIC) at BNL have studied the hot and dense medium created in heavy-ion collisions
Any suppression of the charged-hadron per-trigger yields in the away-side jets in central Au+Au collisions is quantified by contrasting to the per-trigger yields measured in p + p collisions, via the ratio of integrated yields, I A A [11,12] (defined in Eq (8))
The data were taken by the Solenoidal Tracker at Relativistic Heavy IonCollider (RHIC) (STAR)
Summary
Experiments at the Relativistic Heavy IonCollider (RHIC) at BNL have studied the hot and dense medium created in heavy-ion collisions. The suppression of high-transverse momentum (pT ) inclusive hadrons [1–3], indicative of jet quenching, corroborates the conclusion that the medium created is opaque to colored energetic partons [4–7] This phenomenon can be understood as a result of the medium-induced radiative energy loss of a hard-scattered parton as it traverses the Quark Gluon. Direct photons are produced during the early stage of the collision, through leading-order pQCD processes such as quark–gluon Compton scattering (qg → qγ ) and quark–antiquark pair annihilation (qq → gγ ) In these processes the transverse energy of the trigger photon approximates the initial pT of the outgoing recoil parton, before the recoiling (“away-side”) parton likely loses energy while traversing the medium and fragments into a jet.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
