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arXiv 1904.01243hep-ph
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低双光子质量超周边重离子碰撞中的光-光散射

Light-by-light scattering in ultra-peripheral heavy-ion collisions at low diphoton masses

Mariola Klusek-Gawenda, Ronan McNulty, Rainer Schicker, Antoni Szczurek

备注：
15 pages, 8 figures
发表信息：
Phys. Rev. D 99, 093013 (2019)
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摘要：

本文研究了质量范围为$W_{γγ} < 5$ GeV的光子-光子散射。我们扩展到低质量范围内的赝标共振$η$，$η^{'}(958)$有助于双光子的最终状态的光生的$W_{γγ}>$ 5 GeV的这个横截面的早期计算。我们提出了作为双光子质量$M_{γγ}$的函数的基本光子-光子截面，由轻子和夸克环图得到，以及由共振$η$，$η^{'}(958)$，$η_c(1S)$，$η_c(2S)$，$χ_{c0}(1P)$的γ-γ衰变分支分数得到的可见截面。通过将重离子光子通量折叠到基元截面中，得到了$\sqrt{s_{NN}}$ = 5.02 TeV的超周边Pb-Pb碰撞的相应截面.我们考虑的主导背景的双光子的最终状态所产生的伽马衰变的光生$π^{0}$ -对。这种$π^{0}$ -对有助于当四个衰变光子中只有两个在实验接受范围内，而其他两个光子逃逸未检测到的背景。我们通过对两个光子的横动量的不对称性施加削减来减少这种背景，并指出如何使用多变量边带分析来进一步抑制背景。我们提出的横截面的信号和背景中快度$|η| <$ 0.9，并在前进的快度范围2.0 $< η<$ 4.5。

英文摘要：

We present a study of photon-photon scattering in the mass range $W_{γγ} < 5$ GeV. We extend earlier calculations of this cross section for $W_{γγ}>$ 5 GeV into the low mass range where photoproduction of the pseudoscalar resonances $η$, $η^{'}(958)$ contributes to two-photon final states. We present the elementary photon-photon cross section as a function of diphoton mass $M_{γγ}$ arising from lepton and quark loop diagrams, and the visible cross section obtained with the gamma-gamma decay branching fractions of the resonances $η$, $η^{'}(958)$, $η_c(1S)$, $η_c(2S)$, $χ_{c0}(1P)$. We derive the corresponding cross sections in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV by folding the elementary cross section with the heavy-ion photon fluxes. We consider the dominating background of the two-photon final state which arises from gamma decays of photoproduced $π^{0}$-pairs. Such $π^{0}$-pairs contribute to the background when only two of the four decay photons are within the experimental acceptance, while the other two photons escape undetected. We reduce this background by applying cuts on asymmetries of transverse momenta of the two photons and indicate how the background can be further suppressed using a multivariate sideband analysis. We present the cross section for the signal and the background at midrapidity $|η| <$ 0.9, and in the forward rapidity range 2.0 $< η<$ 4.5.

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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