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arXiv 1801.04320nucl-thhep-ph
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外围重离子碰撞中双轻子对的双光子产生

Two-photon production of dilepton pairs in peripheral heavy ion collisions

Spencer R. Klein

摘要:

STAR合作观测到相对论性重离子碰撞中$e^+e^-$对的过量产生,超过了强子产生模型的预期。过剩对具有横动量$p_T < 150\ {\rm MeV}/c$,在外围的金-金和铀-铀碰撞中最为突出。这些电子对在$J/ψ$质量处有一个峰值,但包括一个宽的连续谱,其电子对不变质量从400 MeV/c $^2$到2.6 GeV/c $^2$。ALICE协作组在外围铅-铅碰撞中观察到类似的过剩,但仅在$J/ψ$质量下,没有相应的连续体。本文计算了$e^+e^-$对双光子产生的截面和运动学,与STAR数据基本一致。计算基于STARlight模拟代码,该代码基于Weizsäcker-Williams虚拟光子方法。STAR连续谱观测与$e^+e^-$对的双光子产生是相容的。ALICE分析要求单个μ介子$p_T$大于1 GeV/c,这就消除了几乎所有的双光子相互作用对,同时留下了大部分的$J/ψ$衰变。

英文摘要:

The STAR collaboration has observed an excess production of $e^+e^-$ pairs in relativistic heavy ion collisions, over the expectations from hadronic production models. The excess pairs have transverse momenta $p_T < 150\ {\rm MeV}/c$ and are most prominent in peripheral gold-gold and uranium-uranium collisions. The pairs exhibit a peak at the $J/ψ$ mass, but include a wide continuum, with pair invariant masses from 400 MeV/c$^2$ up to 2.6 GeV/c$^2$. The ALICE Collaboration observes a similar excess in peripheral lead-lead collisions, but only at the $J/ψ$ mass, without a corresponding continuum. This paper presents a calculation of the cross-section and kinematic for two-photon production of $e^+e^-$ pairs, and find general agreement with the STAR data. The calculation is based on the STARlight simulation code, which is based on the Weizsäcker-Williams virtual photon approach. The STAR continuum observations are compatible with two-photon production of $e^+e^-$ pairs. The ALICE analysis required individual muon $p_T$ be greater than 1 GeV/c; this eliminated almost all of the pairs from two-photon interactions, while leaving most of the $J/ψ$ decays.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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