Study of isolated-photon and jet momentum imbalance in pp and PbPb collisions

Abstract

In this paper, we study the production of isolated-photon plus a jet in pp and P bP b collisions, which can be used as an important probe to the jet transport property in quark gluon plasma created in heavy ion collisions. Normally, there are two types of observables associated with the production of isolated-photon plus a jet, namely, the azimuthal angular correlation and the transverse momentum imbalance. To understand both observables in the full kinematical region, we need to employ the perturbative QCD calculation, which takes into account the hard splitting of partons, together with the Sudakov resummation formalism, which resums soft gluon splittings. Furthermore, by introducing energy-loss into the system, we calculate the enhancement of the momentum imbalance distribution for AA as compared to pp collisions and make predictions for future unfolded experimental data. In addition, in order to extract the jet transport coefficient more precisely in our numerical calculation, we also distinguish quark jets from gluon jets, since they interact with quark gluon plasma with different strengths. This work provides a reliable theoretical tool for the calculation of the gamma-jet correlation, which can lead us to a more precise extraction of the jet transport coefficient in relativistic heavy-ion collisions. I. INTRODUCTIONCreated in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and later at the Large Hadron Collider (LHC) at CERN, the Quark-Gluon Plasma (QGP) is undoubtedly one of the most interesting discoveries in relativistic heavyion collision experiments. A lot of efforts have been devoted to unravel the mysteries of this strongly-coupled fluid, which is also related to the very early stages of the universe.Due to multiple scatterings with QGP which induces additional gluon radiations, high energy jets traversing QGP medium can lose a significant fraction of their energy [1][2][3][4][5][6][7][8][9]. In the Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPS-Z) jet energy loss formalism [2][3][4][5], the signature of energy loss is characterized by the so-called jet transport coefficientq [10][11][12], which is defined as transverse momentum square transfer per unit length and reflects the density of QGP medium. In particular, early efforts in the quantitative extraction of the jet-transport coefficient from the JET collaboration were performed by calculating the nuclear modification factor (R AA ) for single hadron production using different energy-loss models, by comparing between RHIC and LHC experimental data on nucleus-nucleus (AA) collision and elementary hadron-hadron (pp) collisions [13].At the LHC, dijet transverse momentum imbalance has become an important gateway to quantitatively study the properties of quark-gluon plasma created in heavy-ion collisions. In particular, its difference between P bP b and pp collisions [14-16] reveals that high energy jets tend to lose a significant amount of energy when traversing QGP medium created in P bP b collisions [17][18][19][20][21][22][23][24]...

Resummation of boson-jet correlation at hadron colliders

“…We find that the resummation formula used in [24,25] give the same result at LL level. The double logarithms in (4.2) arise from soft radiation along the three collinear directions.…”

“…The situation is similar in di-jet production where q T is defined as the vector sum of the transverse momenta of the two leading jets, and the resummation of log(Q/q T ) at next-to-leading logarithmic (NLL) accuracy without non-global logarithms (NGLs) [20,21] was carried out using the CSS formalism in [22,23]. Similarly, the log(Q/q T ) resummation at NLL level was also performed for photon(γ)+jet [24], Z+jet [25] and top quark+jet production [26,27]. More recently, the NLL resummation in γ+jet production was also carried out using SCET [28].…”

“…Through interactions with the medium, jets in the event can be significantly modified while the color-singlet boson remains intact that can serve as a robust reference of the hard scattering process. This makes boson+jet production a useful channel for studying the properties of QGP though the relation between transverse momentum broadening and energy loss of jets in high-energy nuclear collisions [45], which requires a proper resummation of large logarithms [24,46,47]. The kinematic information of the boson+jet system has been explored quite extensively [48][49][50][51][52][53][54].…”

“…Let us compare our NLL resummed expression with those in [24,25,28]. The large logarithms log(Q/q T ) were resummed in γ+jet [24] and Z+jet [25] events at NLL level using the CSS formalism [1]. In these references, the calculations were carried out in the small R limit, but the terms with log R in the coefficients are not completely resummed.…”

“…After performing this transformation, the Z boson and the leading jet are not back to back in the transverse plane. Hence, we obtain the distribution of the azimuthal angle ∆φ(Z, j 1 ) In principle, one needs to perform a matching between the resummed result and the fixedorder calculation to calculate the azimuthal angle decorrelation (see, e.g., [22,24]). However, as we show in figure 6, at high p T our resummed result gives a good description even up to q T ∼ p T .…”