Zeroing in on jet quenching: a PHENIX perspective

Abstract

We review recent progresses on jet quenching measurements by PHENIX. With increased statistics, PHENIX has gone beyond the single hadron suppression R AA , and made measurements on multiple jet quenching observables, such as v 2 , I AA and v I AA 2 . We argue that, by combining these observables together, one can achieve a better understanding of the energy loss mechanism. We present new γ-hadron correlation results with associated hadrons extended to low p T ; an enhancement has been observed, suggesting a contribution of genuine medium response that is relatively unbiased by the initial geometry fluctuations. The status of full jet reconstruction and future perspective of PHENIX jet quenching program are discussed.

${\cal O}(α_s^3)$ analysis of inclusive jet and di-jet production in heavy ion reactions at the Large Hadron Collider

“…Jet production and modification in high-energy nucleusnucleus collisions have been proposed as new ways to unravel the properties of the hot and dense QCD medium and to elucidate the mechanisms of in-medium parton shower formation [13,14,18]. Measurements of jets in heavy ion collisions have now become available [15,16,17]. With this in mind, in this Letter we presented first O(α 3 s ), O(α 2 s α rad s ) results for the single and double inclusive jets production rates in p+p and central Pb+Pb collisions at the LHC at center-of-mass energies per nucleon-nucleon pair √ s NN = 7 TeV and 2.76 TeV, respectively.…”

“…Preliminary RHIC results suggest that the jet size dependence of jet attenuation may have already been observed in Au+Au and Cu+Cu reactions at RHIC [15,16,17]. However, before we discuss di-jet production in heavy ion reactions, we comment on the difficulties related to the measurement of jet observables.…”

“…On the other hand, the modification of jets in dense QCD matter requires much deeper understanding of the in-medium parton shower production mechanisms [13]. For inclusive jets, tree-level calculations can be used to discuss qualitatively the effects of finalstate interactions but O(α 3 s ) results [14] are necessary for quantitative comparison to the preliminary jet experimental data in gold-gold (Au+Au) and copper-copper (Cu+Cu) reactions at RHIC [15,16,17]. For tagged jets and di-jets lowest order, for example O(α 2 s ), O(G F α s ) and O(α em α s ), calculations fail to describe even qualitatively the double differential momentum distributions [18] and one-loop pQCD results are required.…”

From RHIC to LHC: First lessons

“…There is no evidence for deflection of the away-side jet, both at the LHC and RHIC as shown in Fig. 6 [17,18].…”

“…-Yet, equally strong asymmetry modification. Figure 6: Angular correlations of dijets (∆φ = φ jet1 − φ jet2 ) in Cu+Cu collisions at RHIC from PHENIX (left panel) [17] and in Pb+Pb collisions at LHC from ATLAS (right panel) [18]. • Energy and momentum balance.…”