Nabeebaccus, Saad and Schoenleber, Jakob and Szymanowski, Lech and Wallon, Samuel (2025) Breakdown of collinear factorization in the exclusive photoproduction of a π0γ pair with large invariant mass. PHYSICAL REVIEW D, 111 (3): 034040. ISSN 2470-0010, 2470-0029
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We study the exclusive photoproduction of a pi 0 gamma pair with large invariant mass M gamma 2 pi, which is sensitive to the exchange of either two quarks or two gluons in the t channel. In this paper, we show that the process involving two-gluon exchanges does not factorize in the Bjorken limit at the leading twist. This can be explicitly demonstrated by the fact that there exist diagrams, which contribute at the leading twist, for which Glauber gluons are trapped, due to the pinching of the contour integration of both the plus and minus component of the Glauber gluon momentum. For the same reason,pi 0-nucleon scattering to two photons also suffers from the same issue. On the other hand, we stress that there are no issues with respect to collinear factorization for the quark channels. By considering an analysis of all potential reduced diagrams of leading pinch-singular surfaces, we argue that the quark channel is safe from Glauber pinches, and therefore, a collinear factorization in that case follows through without any problems. This means that processes where gluon exchanges are forbidden, such as the exclusive photoproduction of pi gamma and rho 0;gamma, are unaffected by the factorization breaking effects we point out in this paper.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | MESON PRODUCTION; ANNIHILATION PROCESSES; ELECTROPRODUCTION; DIVERGENCES; HADRON |
| Subjects: | 500 Science > 520 Astronomy & allied sciences 500 Science > 530 Physics |
| Divisions: | Physics > Institute of Theroretical Physics |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 16 Jul 2026 06:28 |
| Last Modified: | 16 Jul 2026 06:28 |
| URI: | https://pred.uni-regensburg.de/id/eprint/66953 |
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