Harmonic decomposition of three-particle azimuthal correlations at energies available at the BNL Relativistic Heavy Ion Collider

Abstract

We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √ sNN = 7.7 to 200 GeV using the STAR detector. The quantity cos(mφ1 + nφ2 − (m + n)φ3) , with φ being the azimuthal angles of the particles is evaluated as a function of √ sNN, collision centrality, transverse momentum, pT , pseudo-rapidity difference, ∆η, and harmonics (m and n). These data provide detailed information on global event properties like the three dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on ∆η is observed for most harmonic combinations which is consistent with breaking of longitudinal boost invariance. An interesting energy dependence is observed when one of the harmonics m, n, or m + n is equal to two, for which the correlators are dominated by the two particle correlations relative to the secondharmonic event-plane. These measurements can be used to constrain models of heavy-ion collisions over a wide range of temperature and baryon chemical potential. Heavy nuclei are collided at facilities like the Relativis-116 tic Heavy Ion Collider (RHIC) and the Large Hadron 117 Collider (LHC) in order to study the emergent proper-118 ties of matter with quarks and gluons as the dominant degrees-of-freedom: a quark-gluon plasma (QGP) [1-4]. 120 The QGP is a form of matter that existed in the early 121 universe when its ambient temperature was more than 155 MeV or 200 thousand times hotter than the center 123 of the sun [5, 6]. As temperatures drop, quarks and glu-124 ons no longer possess the energy necessary to overcome 125 the confining forces of QCD and they become confined 126 into color neutral hadrons and the QGP transitions into a 127 gas of hadrons [7]. This transition occurred in the early 128 universe at about one microsecond after the big bang. 129 Heavy-ion collisions provide the only known method to recreate and study that phase transition in a laboratory 131 setting. 132 To provide the clearest possible picture of this phase 133 transition, a beam energy scan was carried out at RHIC 134 with collision energies ranging from √ s NN =200 GeV 135 down to 7.7 GeV. Lowering the beam energy naturally 136 reduces the initial temperature (T) of the matter cre-137 ated in the collisions, as well as increases the baryon 138 chemical potential µ B , providing information on how the 157 dence of the correlations on the azimuthal angle between 158 particles ∆φ = φ 1 − φ 2 has proven to be particularly in-159 formative. Data have revealed that even when particle 160 pairs are separated by large angles in the longitudinal di-161 rection (large ∆η), they remain strongly correlated in the 162 azimuthal direction. One example of these correlations is 163 a prominent ridge-like structure that can be seen in the 164 two-particle correlations; and this ridge is associated with 165 an enhanced correlation near ∆φ ∼ 0 and π and a long-166 range structure in ∆...

Multiparticle and charge-dependent azimuthal correlations in heavy-ion collisions at the Relativistic Heavy-Ion Collider

“…7 shows a compilation of C mnk for m = 1 and various other combinations of k = n + 1. For n = 2 and n = 3 agreement with experimental data from the STAR Collaboration [2] is good, however, for n = 1, we see a large difference between the calculation and the experimental data. Even the sign of C 112 is calculated to be opposite to the experimentally determined one.…”

“…Fig. 6 shows comparisons between the theory calculations and three particle correlations measured by the STAR Collaboration [2]. A factor of N 2 part is multiplied to scale out the trivial dilution of correlation with the increase of triplets.…”

“…Recent experimental results from RHIC (and the LHC) go beyond the conventional two-particle correlations and focus on the precision measurements of multi-particle azimuthal correlations, including their charge dependence [1][2][3][4][5].…”

“…The two-particle anisotropic flow coefficient vn{2} for charged hadrons in Au+Au collisions at 200 GeV compared with experimental data from the STAR Collaboration[2,71].…”

A flow paradigm in heavy-ion collisions

“…Unlike the cumulants of harmonic flow which reflect the fluctuation porperties of the colliding systems, to a large extent, flow correlations measure the correlation properties of flow angles on an event-by-event basis. There are several types of correlators of the mixed harmonics that have been investigated in experiments, including event-plane correlations first measured by the ATLAS collaboration ρ mn [100], the symmetric cumulants SC(m, n) proposed by the ALICE collaborations [101], and the three plane event-plane correlators recently measured by the STAR collaboration at the RHIC energy [102,103]. Fig.…”