夸克-胶子等离子体中喷注淬火效应的味道依赖

Experimental evidences from RHIC and LHC indicate the formation of a strongly coupled quark-gluon plasma(QGP) in high energy heavy ion collisions. Jets produced from hard collisions will interact with QGP and lose their energy while they propagate through QGP along its trajectory. This is referred to as jet quenching. We have established a model to calculate the whole process of jet evolution in QGP within the higher-twist approach in our previous study...In this proposal, we plan to study the flavor dependence of jet quenching within the high-twist approach. Since the energy loss in QGP for a quark and a gluon are quite different, the medium modification of their transverse momentum spectra after jet quenching should also be different. This difference could also manifest in the final hadron spectra, the flavor composition for example. Consequently, ratio of pion, kaon and proton yield will be influenced by different jet quenching for quarks and gluons. We can then extract properties of QGP indirectly from experimental data on relative hadron yields. Another topic in this proposal is about the puzzle of jet quenching for heavy quarks. The energy loss of a heavy quark in QGP was predicted to smaller than a light quark because of “dead cone” effect in the radiative gluon spectra. However, experimental data at both RHIC and LHC show no significant difference in jet quenching for heavy and light quarks. In our model, we can follow the whole evolution process of heavy quark in QGP which can help us to find out what mechanics could contribute mainly for its energy loss. In addition, we will also consider contribution from gluon jet slitting in the final heavy quark spectra. This combined approach can solve the heavy quark puzzle in jet quenching.

实验数据表明在高能重离子碰撞中产生了强耦合的夸克-胶子等离子体(sQGP)。碰撞中产生的大横动量喷注在穿过QGP的过程中，会与QGP相互作用而损失自身的能量,这就是喷注淬火效应。前期研究中,我们在高扭度QCD框架下已经建立起一个完整的模型来计算喷注在QGP中演化的整个过程。本项目主要是利用这一模型考察喷注淬火效应对喷注味道的依赖关系。由于夸克和胶子在QGP中有着不同的能量损失,而它们的横动量谱又会影响末态强子系统的味道组分，我们可以从末态不同强子之间的比例间接得到关于QGP性质的信息。本项目另一个研究重点是关于重味夸克喷注淬火效应的研究。理论上由于胶子辐射“死角”效应的存在, 重味夸克能量损失应该比轻味夸克小，然而实验表明它们并没有明显差别。我们的计算框架可以跟踪重味夸克在QGP中演化的全过程,确定其能量损失的主要机制。同时我们也会考虑胶子喷注碎裂对重味强子的贡献，这样我们将解决这一疑难。

研究夸克胶子等离子体（QGP）的性质是人们理解和研究强相互作用以及色禁闭的重要手段。.大横动量喷注在穿过QGP的过程中会不断地与QGP发生多重散射，并辐射出胶子。一直以来人们都关注于这个过程中喷注的能量损失，我们发现这个过程中还存在味道转化效应。为了得到较为干净的味道关联背景，本项目选择从电子-金核碰撞着手，研究末态强子系统的味道组分与初始喷注的味道之间的关联。我们的研究证实了在部分子穿过核环境的过程中的确会同时伴随有味道的演化。而且味道的演化对于核环境的胶子密度非常敏感。所以本项目为核物质中喷注演化指出了另外一种重要而且灵敏的测量指标——末态强子的味道组分关联。.另一方面，喷注的演化过程与QGP的演化息息相关。近几年来，QGP中的量子反常输运现象及其在高能重离子碰撞中的实验信号越来越被学界所重视。这些反常输运现象包括手征磁效应（CME）和手征涡旋效应（CVE）。为了确认CME，本项目提出可以通过非对称重核碰撞来将其贡献从背景效应中区分出来。我们计算了铜-金核碰撞过程中所产生的电磁场及其对电荷分离效应的影响。我们发现如果是CME的贡献占主导，铜-金核碰撞中产生的沿反应面方向的电场会强烈的压低双粒子关联函数，甚至会使其反号。本项目还提出了利用同重异位素碰撞实验来区分手征磁效应和背景效应。由于同重异位素碰撞过程中的流体背景效应几乎一样，而其带电量的明显差别将导致手征磁效应有明显差异。所以这将是一个区分CME信号和背景的非常有效的手段。此外，为了定量研究手征涡旋效应，本项目详细计算了重离子碰撞中产生的初始涡旋度的各项性质，发现QGP中的涡旋度远高于任何已知的流体。