In collisions of ultrarelativistic nuclei, photon-tagged jets provide a unique opportunity to compare jet production and modification due to parton shower formation and propagation in strongly interacting matter at vastly different center-of-mass energies. We present first results for the cross sections of jets tagged by an isolated photon to O(α(em)α(s)(2)) in central Au+Au reactions with sqrt[s(NN)] = 200 GeV at RHIC and central Pb + Pb reactions with sqrt[s(NN)] = 2.76 TeV at LHC. We evaluate the increase in the transverse momentum imbalance of the observed γ + jet state, induced by the dissipation of the parton shower energy due to strong final-state interactions. Theoretical predictions to help interpret recent and upcoming experimental data are presented.

The transverse momentum spectrum of η meson in relativistic heavy-ion collisions is studied at the Next-to-Leading Order (NLO) within the perturbative QCD, where the jet quenching effect in the QGP is incorporated with the effectively medium-modified η fragmentation functions using the higher-twist approach. We show that the theoretical simulations could give nice descriptions of PHENIX data on η meson in both p+p and central Au+Au collisions at the RHIC, and also provide numerical predictions of η spectra in central Pb + Pb collisions with √ sNN = 2.76 TeV at the LHC.The ratios of η/π 0 in p + p and in central Au + Au collisions at 200 GeV are found to overlap in a wide pT region, which matches well the measured ratio η/π 0 by PHENIX. We demonstrate that, at the asymptotic region when pT → ∞ the ratios of η/π 0 in both Au + Au and p + p are almost determined only by quark jets fragmentation and thus approach to the one in e + e − scattering; in addition, the almost identical gluon (quark) contribution fractions to η and to π result in a rather moderate variation of η/π 0 distribution at intermediate and high pT region in A + A relative to that in p+p; while a slightly higher η/π 0 at small pT in Au+Au can be observed due to larger suppression of gluon contribution fraction to π 0 as compared to the one to η. The theoretical prediction for η/π 0 at the LHC has also been presented. PACS numbers: 12.38.Mh; 25.75.-q; 13.85.NiThe strong suppression of single hadron production at large transverse momentum [1,2] has provided the convincing evidence of the jet quenching phenomena discovered in relativistic heavy-ion collisions (HIC) [3]. Extensive phenomenological investigations [4-9] and experimental measurements [10-16] on the suppression of single hadron spectra at high p T have been carried out at both the RHIC and the LHC. As the first observable of jet quenching phenomena, the yield suppression of inclusive hadrons is arguably the most thoroughly studied quantity of jet quenching, and provides an indispensible tool to extract the properties of the hot medium created in nucleus-nucleus collisions by comparing theoretical calculations with experimental measurements, such as the jet transport coefficientq [17]. The interplay between theory and experiment on the single hadron production will help constraining the longitudinal distribution of parton energy loss in hot/dense QCD medium, and better understanding the jet-medium interactions after being combined with studies of full jets which also shed light on the angular distribution of the medium-induced gluon radiation and thus constrain the transverse distribution of parton energy loss as well [18][19][20][21][22][23].So far, most of the theoretical calculations on single hadron productions in HIC focus on π meson or charged hadrons (where π also giving a predominant contribu- * tion), and there are very few studies on other identified hadrons [24][25][26][27]. We note that η meson is the second important source of decay electrons and photons just after the π 0 , and...

In this work, we pave the way to calculate the productions of ω and K 0 S mesons with large p T in p+p and A+A collisions both at RHIC and LHC. The fragmentation functions (FFs) of the ω meson in vacuum at nextto-leading order (NLO) are obtained by evolving the NLO DGLAP evolution equations with rescaled ω FFs at initial scale Q 2 0 = 1.5 GeV 2 from a broken SU(3) model, and the FFs of K 0 S in vacuum are taken from AKK08 parametrization directly. Within the framework of the NLO pQCD improved parton model, we arrive at good descriptions of the experimental data on ω and K 0 S in p+p both at RHIC and LHC. With the higher-twist approach, to take into account jet quenching effect by medium-modified FFs, nuclear modification factors for ω meson and K 0 S meson both at RHIC and LHC are presented with different sets of jet transport coefficientsq 0. Then we make a global extraction ofq 0 both at RHIC and LHC by confronting our model calculations with all available data on six identified mesons: π 0 , η, ρ 0 , φ, ω, and K 0 S. The minimum value of total χ 2 /d.o. f for productions of these mesons gives the best value ofq 0 = 0.5 GeV 2 /fm for Au+Au collisions with √ s NN = 200 GeV at RHIC, andq 0 = 1.2 GeV 2 /fm for Pb+Pb collisions with √ s NN = 2.76 TeV at LHC, respectively, with the QGP spacetime evolution given by the event-by-event viscous hydrodynamics model IEBE-VISHNU. With these global extracted values ofq 0 , nuclear modification factors of π 0 , η, ρ 0 , φ, ω, and K 0 S in A+A collisions are presented, and predictions of yield ratios such as ω/π 0 and K 0 S /π 0 at the highp T regime in heavy-ion collisions both at RHIC and LHC are provided.

Heavy flavor physics in high-energy heavy-ion collisions is a promising and active area to study the mass dependence of the " jet quenching " effects both at the RHIC and the LHC. In this talk, we present the first theoretical study on the D 0 meson radial distributions relative to the jet axis both in p+p and Pb+Pb collisions at √ s NN = 5.02 TeV, where a nice agreement of our results with experimental data is observed. The in-medium parton propagations are described by a Monte Carlo transport model which uses the next-to-leading order (NLO) plus parton shower (PS) event generator SHERPA as input and includes elastic (collisional) and inelastic (radiative) in-medium interaction of heavy flavor jet. We find that, at low D 0 meson p T , the radial distribution significantly shifts to larger radius indicating a strong diffusion effect, and the diffusion effects decrease quickly with p T ,which is consistent with the recent CMS measurements. We demonstrate that the angular deviation of charm quarks is sensitive to D s but notq, which may provide new constrains on the collisional and radiative heavy quark energy loss.

We calculate φ meson transverse momentum spectra in p+p collisions as well as their nuclear suppressions in central A+A collisions both at the RHIC and the LHC in LO and NLO with the QCDimproved parton model. We have included the parton energy loss effect in hot/dense QCD medium with the effectively medium-modified φ fragmentation functions in the higher-twist approach of jet quenching. The nuclear modification factors of φ meson in central Au+Au collisions at the RHIC and central Pb+Pb collisions at the LHC are provided, and a nice agreement of our numerical results at NLO with the ALICE measurement is observed. Predictions of yield ratios of neutral mesons such as φ/π 0 , φ/η and φ/ρ 0 at large pT in relativistic heavy-ion collisions are also presented for the first time.PACS. 12.38.Mh Quark-gluon plasma -25.75.-q Relativistic heavy-ion collisions -13.85.Ni Inclusive production with identified hadrons