Abstract
We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions for the trigger and associated particle transverse-momentum ranges of $1<p_T^t<10$~GeV/$c$ and $0.5<p_T^a<10$~GeV/$c$. After subtraction of an underlying event using a model that includes higher-order azimuthal anisotropy $v_2$, $v_3$, and $v_4$, the away-side yield of the highest trigger-\pt ($p_T^t>4$~GeV/$c$) correlations is suppressed compared to that of correlations measured in $p$$+$$p$ collisions. At the lowest associated particle $p_T$ ($0.5<p_T^a<1$ GeV/$c$), the away-side shape and yield are modified relative to those in $p$$+$$p$ collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-$p_T$ trigger correlations ($2<p_T^t<4$ GeV/$c$), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle $\Psi_2$ and $\Psi_3$. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the $\Psi_2$ event plane. This asymmetry and the measured suppression of the pair yield out of plane is consistent with a path-length-dependent energy loss. No $\Psi_3$ dependence can be resolved within experimental uncertainties.
Highlights
The PHENIX detector [65] was designed to measure charged hadrons, leptons, and photons to study the nature of the quark gluon plasma (QGP) formed in ultrarelativistic heavy-ion collisions
Charged hadron tracks are reconstructed in the PHENIX central arm spectrometer (CNT), which is comprised of two separate arms, east and west
The results presented are based on an analysis lion minimum-bias events for Au + Au collisions of at
Summary
Energy loss of hard-scattered partons (jet quenching [1]) resulting from the interaction of a colored parton in the quark gluon plasma (QGP) formed in relativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) [2,3,4,5]. Observations of the energy-loss effects mentioned above, especially for lower jet and particle momenta in two-particle correlations, have been obscured due to the much larger contribution from the underlying event at these momenta. Varying the path length by selecting azimuthal orientations relative to the second-order event plane has been explored for single-particle or single-jet observables at high pT [11,64]. Such differential correlations probe the path-length and geometrical dependence of energy loss with more event-by-event sensitivity and extend similar studies of high-pT correlations [16] down to lower pT.
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