分类： 物理学 >> 核物理学 提交时间： 2024-07-17
摘要： We present a theoretical study of the medium modifications on the $p_T$ balance ($x_J$) of dijets in Xe+Xe collisions at $sqrt{s_{NN}}$ = 5.44 TeV. The initial production of dijets is carried out by the POWHEG+PYTHIA8 prescription, which matches the next-to-leading order (NLO) QCD matrix elements with the parton shower (PS) effect. The in-medium evolution in nucleus-nucleus collisions is described by the SHELL model with a transport approach. The theoretical results of the dijet $x_J$ in Xe+Xe collisions exhibit more imbalanced distributions than that in p+p, consistent with the recently reported ATLAS data. By utilizing the Interleaved Flavor Neutralisation, an infrared-and-collinear-safe jet flavor algorithm, to identify the flavor of the reconstructed jets, we classify dijets processes into three categories: gluon-gluon (gg), quark-gluon (qg) and quark-quark (qq), and investigate the respective medium modification patterns and fraction changes of the gg, qg, and qq components of the dijet sample in Xe+Xe collisions. It is shown that the qg component plays a key role in the increased imbalance of the dijet $x_J$ , and especially the $q_1g_2$ (quark-jet-leading) dijets experience more significant asymmetric energy loss than the $g_1q_2$ (gluon-jet-leading) dijets as traversing the QGP. By comparing the $∆⟨x_J⟩$ of inclusive, ccbar and bbbar dijets in Xe+Xe collisions, we observe $∆⟨x_J⟩_{incl.} > ∆⟨x_J⟩_{ccbar} > ∆⟨x_J⟩_{bbbar}$. Moreover, $ρ_{Xe,Pb}$, the ratios of nuclear modification factors of dijets in Xe+Xe to that in Pb+Pb, are calcualted, which indicates that the yield suppression of dijets in Pb+Pb is more pronounced than that in Xe+Xe due to the larger radius of the lead nucleus.
分类： 物理学 >> 核物理学 提交时间： 2024-06-03
摘要： The medium temperature $T$ dependence of jet transport coefficient $ hat q$ is studied via nuclear modification factor $R_{AA}(p_{ rm T})$ and elliptical flow parameter $v_2(p_{ rm T})$ for large transverse momentum $p_{ rm T}$ hadrons in high-energy nucleus-nucleus collisions. Within a next-to-leading order perturbative QCD parton model for hard scatterings with modified fragmentation functions due to jet quenching controlled by $ hat q$, we check the suppression as well as the azimuthal anisotropy for large $p_{ rm T}$ hadrons, and extract $ hat q$ by global fits to $R_{AA}(p_{ rm T})$ and $v_2(p_{ rm T})$ data in $A+A$ collisions at RHIC and the LHC, respectively. Numerical results from the best fits show that $ hat q/T^3$ goes down with the local medium temperature $T$ in the parton jet trajectory. Compared with the case of a constant $ hat{q}/T^3$, the going-down $T$ dependence of $ hat{q}/T^3$ makes a hard parton jet to lose more energy near $T_c$ and therefore strengthens the azimuthal anisotropy for large $p_{ rm T}$ hadrons. As a result, $v_2(p_{ rm T})$ for large $p_{ rm T}$ hadrons is enhanced by about 10 % to fit data better at RHIC/LHC. Considering the first-order phase transition from QGP to the hadron phase and additional energy loss in the hadron phase, $v_2(p_{ rm T})$ is again enhanced by 5-10 % at RHIC/LHC.
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