Breakdown of collinear factorization in the exclusive photoproduction of a ${\pi }^0\gamma$ pair with large invariant mass

Journal Article · 25 February 2025 · Physical Review. D.

DOI: https://doi.org/10.1103/PhysRevD.111.034040 · OSTI ID:2524083

Nabeebaccus, Saad ; Schönleber, Jakob ; Szymanowski, Lech ; Wallon, Samuel

We study the exclusive photoproduction of a ${\pi }^0\gamma$ pair with large invariant mass $M_{\gamma \pi }^2$ , 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 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 are , due to the pinching of the contour integration of 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 ${\pi }^{\pm }\gamma$ and ${\rho }^{0,\pm }\gamma$ , are unaffected by the factorization breaking effects we point out in this paper. Published by the American Physical Society 2025

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: European Union’s Horizon 2020 research and innovation program; French Agence Nationale de la Recherche (ANR); National Science Center in Poland; Research Unit FOR2926; Royal Society; Science and Technologies Facilities Council (STFC); USDOE; USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: SC0012704
• OSTI ID: 2524083
• Report Number(s): BNL--228010-2025-JAAM; 034040
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 3 Vol. 111; ISSN PRVDAQ; ISSN 2470-0010
• Publisher: American Physical SocietyCopyright Statement
• Country of Publication: United States
• Language: English