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arXiv 2401.17656hep-phhep-exnucl-exnucl-th
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光子-介子对的独家光产生：探测GPDs的一类新观测量

Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

Goran Duplančić, Saad Nabeebaccus, Kornelija Passek-K., Bernard Pire, Jakob Schönleber, Lech Szymanowski, Samuel Wallon

备注：
11 pages, 3 figures. Presented at 25th International Spin Physics Symposium (SPIN 2023), Durham, NC, USA
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AI总结：

本文提出光子-介子对独家光产生作为探测GPDs的新观测量，可研究x依赖性并访问手征奇GPDs，但发现含胶子贡献的过程存在因子化破坏问题。

摘要：

我们讨论了具有大$p_{T}$的光子-介子对的独家光产生，作为探测广义部分子分布（GPDs）的一个通道。与其他$2\ o3$独家过程类似，该通道使我们能够更好地研究GPDs的$x$依赖性，而$2\ o2$过程如深度虚康普顿散射（DVCS）仅提供“矩型”信息。此外，它还在前导扭曲下提供了访问手征奇GPDs的可能性，这些GPDs在实验上仍完全未知。在本会议录的第一部分，我们展示了对于带电π介子以及任意电荷和极化ρ介子，在前导阶和前导扭曲下的振幅计算。这些过程仅对夸克GPDs敏感。我们还讨论了在各种实验中测量此类过程的可能性，即JLab、COMPASS、未来的EIC以及LHC的超外围碰撞。特别是在对撞机实验中，可以提取小偏斜度（$<10^{-3}$）下GPDs的依赖性。对于第二部分，我们报告了关于$π^{0}γ$对独家光产生的最新工作，该过程除了夸克GPD通道外，还有来自胶子GPDs的贡献。在后一种情况下，我们证明了由于存在Glauber收缩，该过程的共线因子化失败。我们的发现还意味着其他类似过程，如$π^{0} N \ o γγN$，也遭受同样的问题。另一方面，我们强调，前面讨论的对夸克GPD通道敏感的过程，不受这些因子化破坏效应的影响。

英文摘要：

We discuss the exclusive photoproduction of a photon-meson pair with large $ p_{T} $ as a channel to probe generalised parton distributions (GPDs). Like other $ 2\to3 $ exclusive processes, this channel allows us to better study the $ x $-dependence of GPDs, in contrast to $ 2\to2 $ processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness $ (<10^{-3}) $ can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of $ π^{0}γ$ pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like $ π^{0} N \to γγN $ also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.

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