We present a study of photon-photon scattering in the mass range W γ γ < 5 ? ? GeV . We extend earlier calculations of this cross section for W γ γ > 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 γ γ 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 ( 1 S ) , η c ( 2 S ) , χ c 0 ( 1 P ) . We derive the corresponding cross sections in ultraperipheral Pb-Pb collisions at s N N = 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 .
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机译：我们对Wγγ<5？范围内的光子-光子散射进行研究。 ？ GeV。当Wγγ> 5？时，我们扩展了对该横截面的早期计算。 ？ GeV进入低质量范围，在该质量范围内伪标量共振η，η'（958）的光产生有助于双光子最终状态。我们提出了基本的光子-光子横截面，它是由轻子和夸克回路图产生的双光子质量Mγγ的函数，以及由共振η，η'（958）的伽马-伽马衰变分支分数获得的可见截面。 ，ηc（1 S），ηc（2 S），χc 0（1 P）。我们得出在s N N = 5.02？的超外围Pb-Pb碰撞中的相应截面。 ？通过用重离子光子通量折叠基本截面来实现TeV。我们考虑了两个最终光子最终状态的主要背景，这是由光生π0对的伽马衰变引起的。当四个衰变光子中只有两个在实验接受范围内时，这样的π0对有助于背景，而另外两个光子则未被检测到逃逸。我们通过对两个光子的横向矩的不对称性进行切割来减少背景，并指出如何使用多元边带分析进一步抑制背景。我们介绍了中间快时信号和背景的横截面| η| <0.9，前进速度范围内<2.0 <η<4.5。
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