arXiv 2006.099452020-06nucl-thhep-th

重离子碰撞中的X（3872）输运

X(3872) Transport in Heavy-Ion Collisions

Biaogang Wu, Xiaojian Du, Matthew Sibila, Ralf Rapp

发表信息：: Eur. Phys. J. A 57, 122 (2021)
DOI：: 10.1140/epja/s10050-021-00435-6

摘要：

在重离子碰撞中产生的$X(3872)$粒子被认为是探测其内部结构的另一种方法。为了研究这一猜想，我们进行运输计算的$X(3872)$通过在大型强子对撞机的核碰撞形成的火球。在先前用于charmonia的动力学速率方程方法中，$X(3872)$的形成和解离由两个传输参数控制，即，它的非弹性反应速率和热平衡极限在不断发展的热QCD介质。当平衡极限由原初核子-核子碰撞中的粲产生截面（连同介质中的粲态谱）控制时，结构信息被编码在反应速率中。我们研究了不同的情况下的速率如何影响的中心依赖性和横向动量（$p_T$）的$X(3872)$谱。较大的反应速率与松散结合的分子结构相关，这意味着它在火球演化中比四夸克态形成得晚，因此其最终产额通常要小大约两倍，这与迄今为止大多数聚并模型的计算有质的不同。$p_T$光谱提供了进一步的信息，因为在分子场景中较晚的去耦时间导致了由膨胀火球的蓝移引起的更硬的光谱。

英文摘要：

The production of the $X(3872)$ particle in heavy-ion collisions has been contemplated as an alternative probe of its internal structure. To investigate this conjecture, we perform transport calculations of the $X(3872)$ through the fireball formed in nuclear collisions at the LHC. Within a kinetic-rate equation approach as previously used for charmonia, the formation and dissociation of the $X(3872)$ is controlled by two transport parameters, i.e., its inelastic reaction rate and thermal-equilibrium limit in the evolving hot QCD medium. While the equilibrium limit is controlled by the charm production cross section in primordial nucleon-nucleon collisions (together with the spectra of charm states in the medium), the structure information is encoded in the reaction rate. We study how different scenarios for the rate affect the centrality dependence and transverse-momentum ($p_T$) spectra of the $X(3872)$. Larger reaction rates associated with the loosely bound molecule structure imply that it is formed later in the fireball evolution than the tetraquark and thus its final yields are generally smaller by around a factor of two, which is qualitatively different from most coalescence model calculations to date. The $p_T$ spectra provide further information as the later decoupling time within the molecular scenario leads to harder spectra caused by the blue-shift from the expanding fireball.

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