He Min, Wu Biaogang, Rapp Ralf
Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China.
Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-3366, USA.
Phys Rev Lett. 2022 Apr 22;128(16):162301. doi: 10.1103/PhysRevLett.128.162301.
The production of J/ψ mesons in heavy-ion collisions at the Large Hadron Collider is believed to be dominated by the recombination of charm and anticharm quarks in a hot QCD medium. However, measurements of the elliptic flow (v_{2}) of J/ψ mesons in these reactions are not well described by existing calculations of J/ψ recombination for transverse momenta p_{T}≳4 GeV. We revisit these calculations in two main aspects. Employing the resonance recombination model, we implement distribution functions of charm quarks transported through the quark-gluon plasma using state-of-the-art Langevin simulations and account for the space-momentum correlations of the diffusing charm and anticharm quarks in a hydrodynamically expanding fireball. This extends the relevance of the recombination processes to substantially larger momenta than before. We also revisit the suppression of primordially produced J/ψ's by propagating them through the same hydrodynamic medium, leading to a marked increase of their v_{2} over previous estimates. Combining these developments into a calculation of the p_{T}-dependent nuclear modification factor and v_{2} of inclusive J/ψ production in semicentral Pb-Pb collisions at the LHC, we find a good description of the experimental results by the ALICE Collaboration. Our results thus resolve the abovementioned v_{2} puzzle and imply the relevance of recombination processes for p_{T}'s of up to ∼8 GeV.
人们认为，在大型强子对撞机的重离子碰撞中，J/ψ介子的产生主要由热QCD介质中魅夸克和反魅夸克的重组主导。然而，对于横向动量(p_{T}≳4) GeV的情况，现有J/ψ重组计算并不能很好地描述这些反应中J/ψ介子的椭圆流（(v_{2})）测量结果。我们从两个主要方面重新审视这些计算。采用共振重组模型，我们使用最先进的朗之万模拟来实现通过夸克-胶子等离子体传输的魅夸克的分布函数，并考虑在流体动力学膨胀火球中扩散的魅夸克和反魅夸克的空间动量相关性。这将重组过程的相关性扩展到比以前大得多的动量范围。我们还通过让最初产生的J/ψ介子在相同的流体动力学介质中传播，重新审视对它们的抑制作用，这导致它们的(v_{2})比之前的估计值显著增加。将这些进展结合起来，用于计算大型强子对撞机中半中心铅-铅碰撞中包含J/ψ产生的(p_{T})相关核修正因子和(v_{2})，我们发现ALICE合作组的实验结果得到了很好的描述。因此，我们的结果解决了上述(v_{2})难题，并意味着重组过程对于高达约8 GeV的(p_{T})是相关的。
