Effects of triangular flow on di-hadron azimuthal correlations in relativistic heavy ion collisions

Abstract

Using the AMPT model for relativistic heavy ion collisions, we have studied the di-hadron azimuthal angular correlations triggered by emitted jets in Au+Au collisions at center of mass energy √ sNN = 200 GeV and impact parameter b = 8 fm. A double-peak structure for the associated particles at the away side of trigger particles is obtained after subtracting background correlations due to the elliptic flow. Both the near-side peak and the away-side double peaks in the azimuthal angular correlations are, however, significantly suppressed (enhanced) in events of small (large) triangular flow, which are present as a result of fluctuations in the initial collision geometry. After subtraction of background correlations due to the triangular flow, the away-side double peaks change into a single peak with broad shoulders on both sides. The away side of the di-hadron correlations becomes essentially a single peak after further subtraction of higher-order flows.PACS numbers: 24.10. Lx, 12.38.Mh Collisions of heavy nuclei at the Relativistic HeavyIon Collider (RHIC) have created a hot and dense matter that is believed to consist of deconfined quarks and gluons, as the inferred energy density is much greater than the critical value of ∼ 1 GeV/fm 3 for the formation of a quark-gluon plasma (QGP) [1][2][3][4]. This matter was found to have a very small viscosity and thus behaves like a nearly perfect fluid [5,6]. Among the signatures for the formation of the QGP is the large quenching of energetic jets produced from initial hard collisions, leading to the suppressed production of hadrons with large transverse momenta [7,8]. Further studies of the di-hadron azimuthal angular correlations triggered by emitted jets have provided the possibility of investigating the response of the QGP to the quenched away-side jets [9][10][11]. It was found in these studies that for central and mid-central collisions of heavy nuclei, there existed not only a pronounced peak at the near side of trigger jets but also a broad double-peak structure at their away side [12,13]. Different mechanisms have been proposed to explain this interesting phenomenon, including the medium-induced gluon radiation [14,15], the Mach cone from the shock wave generated by the traversing jet in produced QGP [16,17], the path-length-dependent jet energy loss [18,19], the Cerenkov radiation from the jet [20], the strong parton cascade [21], and the deflection of jets by partons in the QGP [22][23][24]. Also, it was recently pointed out that the so far overlooked large triangular flow, resulting from the non-vanishing triangularity in the initial collision geometry as a result of the spatial fluctuation of participating nucleons [25][26][27], could be responsible for the double-peak structure at the away side of di-hadron correlations [28,29]. This stems from the observation that the azimuthal angular correlations of hadrons resulting from their triangular flow have peaks at 0, 2π/3 and 4π/3, which are similar to the peaks observed in the experimentally measured di-had...

Long-range and short-range dihadron angular correlations in central PbPb collisions at $ \sqrt {{{s_{\text{NN}}}}} $ = 2.76 TeV

“…Measurements of dihadron correlations at RHIC have frequently attempted to subtract or factorize the elliptic flow contribution based on direct v 2 measurements, in order to reveal other features of particle correlations that may provide insight into the interactions between the jets and the medium. However, recent theoretical developments indicate that the interplay between initial-state fluctuations and the subsequent hydrodynamic expansion gives rise to additional Fourier components in the azimuthal particle correlations [25,26,[38][39][40][41][42]. These components need to be treated on equal footing with the elliptic flow component.…”

“…Motivated by recent theoretical developments in understanding the long-range ridge effect in the context of higher-order hydrodynamic flow induced by initial geometric fluctuations, such as the "triangular flow" effect [26,[38][39][40][41][42], an alternative way of quantifying the observed long-range correlations is investigated in this paper. The 1-D ∆φ-projected distribution for 2 < |∆η| < 4 is decomposed in a Fourier series as 2) JHEP07 (2011) where N assoc represents the total number of hadron pairs per trigger particle for a given |∆η| range and (p trig T , p assoc T ) bin.…”

Initial fluctuation effect on harmonic flows in high-energy heavy-ion collisions

“…In fact, because of the nonsmooth profile, coming from the event-byevent fluctuations of participant nucleons, it shows a triangular initial geometry shape can be transferred into momentum space by hydrodynamical evolution. In recent studies, it has been demonstrated that triangular flow significantly contributes on the near-side ridge and away-side double bumps in two-particle azimuthal correlations [16,17]. As a probe, triangular flow is believed to provide more information about the formed hot and dense matter.…”

Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at $\sqrt{s_{NN}}= 2.76\ \mbox{TeV}$

“…Concentrating on large | η|, previous measurements at RHIC established some of the properties of the so-called "ridge" [4,6,9], an enhancement of pairs with | φ| ≈ 0. While a variety of theoretical models have been proposed to interpret the ridge phenomena as a consequence of jet-medium interactions [14][15][16][17][18][19], recent theoretical developments indicate that, because of event-byevent fluctuations in the initial shape of the interacting region, sizeable higher-order hydrodynamic flow terms could also be induced, e.g., triangular flow [20][21][22][23][24][25][26][27][28]. The triangular flow effect will contribute to the dihadron correlations in the form of a cos(3 φ) component, which also gives a maximum near-side correlation at φ ≈ 0, similarly to the elliptic flow contribution.…”