$γ$-hadron spectra in p + Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

Abstract

Under the assumption that a quark-gluon plasma droplet is produced and its evolution can be described by hydrodynamics in p + A collisions, γ-triggered hadron spectra are studied within a next-to-leading-order perturbative QCD parton model with the medium-modified parton fragmentation functions. The initial conditions and space-time evolution of the small QGP droplet are provided by the superSONIC hydrodynamic model simulations and parton energy loss in such a medium is described by the high-twist (HT) approach. The scaled jet transport coefficient q/T 3 in this HT approach is extracted from single hadron suppression in central A + A collisions at the same colliding energy. Numerical results for this scenario show that γ-hadron spectra at p γ T = 12 − 40 GeV/c are suppressed by 5% ∼ 10% in the most central 0 -10% p + Pb collisions at √ sNN = 5.02TeV. The suppression becomes weaker at higher transverse momentum of the γ trigger. As a comparison, γ-hadron suppression in Pb + Pb collisions at √ sNN = 2.76 and 5.02 TeV is also predicted.

Extracting jet transport coefficient via single hadron and dihadron productions in high-energy heavy-ion collisions

“…The partonic cross section dσ ab→γd /d t only includes Compton scattering subprocesses qg → qγ and annihilation sub-processes q q → gγ. Fragmentation photons are ignored here due to their small contribution with isolation cuts [59,61]. Then, the cross-section for γ-hadron process is [72],…”

“…The direct photon spectra from the above NLO pQCD parton model have been compared to the experimental data systematically in Ref. [59] at different colliding energies. The contributions of the fragmentation photons were also found to be less than 10% [61].…”

“…The contributions of the fragmentation photons were also found to be less than 10% [61]. Therefore, direct photon triggered fragmentation functions are sufficient to describe the experimental data with the isolation cut [59]. We therefore will only calculate the direct photon triggered fragmentation functions which are shown in Fig.…”

“…Microscopically, q can be related to the gluon field strength correlation or the local gluon number density of the QCD medium along the light-like trajectory of the hard parton [49,50]. Phenomenological values of q have been extracted through model-to-data comparisons using hadron suppression data [26,36,37,[51][52][53][54][55][56][57][58][59]. Among these studies, the JET Collaboration [53] surveyed five different parton energy loss approaches with a realistic hydrodynamic description of the bulk evolution to determine q from single inclusive hadron suppression in the most central nuclear collisions at both RHIC and LHC.…”

Imaging nuclear modifications on parton distributions with triple-differential dijet cross sections in proton-nucleus collisions

“…In this study, we have only considered the nuclear corrections on the leading-twist PDFs and not focused on the possible higher-twist nuclear effects [44,45]. Besides, since there has been no clear experimental evidence of the possible final-state jet quenching effects in pA collisions [46,47], we have only considered the initial-state CNM effects.…”