A new and detailed measurement of the cross section for hard exclusive neutral-pion muoproduction on the proton was performed in a wide kinematic region, with the photon virtuality Q 2 ranging from 1 to 8 (GeV/ c ) 2 and the Bjorken variable x B j ranging from 0.02 to 0.45. The data were collected at COMPASS at CERN using 160 GeV/ c longitudinally polarised μ + and μ − beams scattering off a 2.5 m long liquid hydrogen target. From the average of the measured μ + and μ − cross sections, the virtual-photon–proton cross section is determined as a function of the squared four-momentum transfer between the initial and final state proton in the range 0.08 (GeV/ c ) 2 < | t | < 0.64 (GeV/ c ) 2 . From its angular distribution, the combined contribution of transversely and longitudinally polarised photons are determined, as well as transverse–transverse and longitudinal–transverse interference contributions. They are studied as functions of four-momentum transfer | t | , photon virtuality Q 2 and virtual-photon energy ν . The longitudinal–transverse interference contribution is found to be compatible with zero. The significant transverse–transverse interference contribution reveals the existence of a dominant contribution by transversely polarised photons. This could provide clear experimental evidence for the chiral-odd GPD E ‾ T . In addition, the existence of a non-negligible contribution of longitudinally polarised photons is suggested by the | t | -dependence of the cross section at x B j < 0.1. Altogether, these results provide valuable input for future modelling of GPDs and thus of cross sections for exclusive pseudo-scalar meson production. Furthermore, they can be expected to facilitate the study of next-to-leading order corrections and higher-twist contributions.
Measurement of the hard exclusive π0 muoproduction cross section at COMPASS / Alexeev, G. D.; Alexeev, M. G.; Alice, C.; Amoroso, A.; Andrieux, V.; Anosov, V.; Augsten, K.; Augustyniak, W.; Azevedo, C. D R; Badelek, B.; Barth, J.; Beck, R.; Beckers, J.; Bedfer, Y.; Bernhard, J.; Bodlak, M.; Bradamante, F.; Bressan, A.; Chang, W. -C; Chatterjee, C.; Chiosso, M.; Chung, S. -U; Cicuttin, A.; Correia, P. M M; Crespo, M. L.; D'Ago, D.; Dalla Torre, S.; Dasgupta, S. S.; Dasgupta, S.; Delcarro, F.; Denisenko, I.; Denisov, O. Yu; Dehpour, M.; Donskov, S. V.; Doshita, N.; Dreisbach, Ch; Dünnweber, W.; Dusaev, R. R.; Ecker, D.; Eremeev, D.; Faccioli, P.; Faessler, M.; Finger, M.; Finger, M.; Fischer, H.; Fl, K. J.; Florian, W.; Friedrich, J. M.; Frolov, V.; Garcia Ordòñez, L. G.; Gavrichtchouk, O. P.; Gerassimov, S.; Giarra, J.; Giordano, D.; Gorzellik, M.; Grasso, A.; Gridin, A.; Grosse Perdekamp, M.; Grube, B.; Gr, M.; Guskov, A.; Haas, P.; Von Harrach, D.; Hoffmann, M.; D'Hose, N.; Hsieh, C. -Y; Ishimoto, S.; Ivanov, A.; Iwata, T.; Jary, V.; Joosten, R.; Jörg, P.; Kabuß, E.; Kaspar, F.; Kerbizi, A.; Ketzer, B.; Khaustov, G. V.; Klein, F.; Koivuniemi, J. H.; Kolosov, V. N.; Kondo Horikawa, K.; Konorov, I.; Korzenev, A. Yu; Kotzinian, A. M.; Kouznetsov, O. M.; Koval, A.; Kral, Z.; Kunne, F.; Kurek, K.; Kurjata, R. P.; Lavickova, K.; Levorato, S.; Lian, Y. -S; Lichtenstadt, J.; Lin, P. -J; Longo, R.; Lyubovitskij, V. E.; Maggiora, A.; Makke, N.; Mallot, G. K.; Maltsev, A.; Martin, A.; Marzec, J.; Matoušek, J.; Matsuda, T.; Menezes Pires, C.; Metzger, F.; Meyer, W.; Mikhasenko, M.; Mitrofanov, E.; Miura, D.; Miyachi, Y.; Molina, R.; Moretti, A.; Nagaytsev, A.; Neyret, D.; Niemiec, M.; Nový, J.; Nowak, W. -D; Nukazuka, G.; Olshevsky, A. G.; Ostrick, M.; Panzieri, D.; Parsamyan, B.; Paul, S.; Pekeler, H.; Peng, J. -C; Pešek, M.; Peshekhonov, D. V.; Pešková, M.; Platchkov, S.; Pochodzalla, J.; Polyakov, V. A.; Quintans, C.; Reicherz, G.; Riedl, C.; Ryabchikov, D. I.; Rychter, A.; Rymbekova, A.; Samoylenko, V. D.; Sandacz, A.; Sarkar, S.; Savin, I. A.; Sbrizzai, G.; Schmieden, H.; Selyunin, A.; Sinha, L.; Sp, D.; Srnka, A.; Stolarski, M.; Sulc, M.; Suzuki, H.; Tessaro, S.; Tessarotto, F.; Thiel, A.; Tosello, F.; Townsend, A.; Triloki, T.; Tskhay, V.; Valinoti, B.; Veit, B. M.; Veloso, J. F C A; Ventura, B.; Vidon, A.; Vijayakumar, A.; Virius, M.; Wagner, M.; Wallner, S.; Zaremba, K.; Zavertyaev, M.; Zemko, M.; Zemlyanichkina, E.; Ziembicki, M.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - STAMPA. - 870:(2025), pp. 139832.1-139832.15. [10.1016/j.physletb.2025.139832]
Measurement of the hard exclusive π0 muoproduction cross section at COMPASS
Bradamante, F.;Bressan, A.;Chatterjee, C.;Chiosso, M.;D'ago, D.;Dalla Torre, S.;Dasgupta, S. S.;Kerbizi, A.;Levorato, S.;Makke, N.;Martin, A.;Matoušek, J.;Molina, R.;Moretti, A.;Sbrizzai, G.;Valinoti, B.;
2025-01-01
Abstract
A new and detailed measurement of the cross section for hard exclusive neutral-pion muoproduction on the proton was performed in a wide kinematic region, with the photon virtuality Q 2 ranging from 1 to 8 (GeV/ c ) 2 and the Bjorken variable x B j ranging from 0.02 to 0.45. The data were collected at COMPASS at CERN using 160 GeV/ c longitudinally polarised μ + and μ − beams scattering off a 2.5 m long liquid hydrogen target. From the average of the measured μ + and μ − cross sections, the virtual-photon–proton cross section is determined as a function of the squared four-momentum transfer between the initial and final state proton in the range 0.08 (GeV/ c ) 2 < | t | < 0.64 (GeV/ c ) 2 . From its angular distribution, the combined contribution of transversely and longitudinally polarised photons are determined, as well as transverse–transverse and longitudinal–transverse interference contributions. They are studied as functions of four-momentum transfer | t | , photon virtuality Q 2 and virtual-photon energy ν . The longitudinal–transverse interference contribution is found to be compatible with zero. The significant transverse–transverse interference contribution reveals the existence of a dominant contribution by transversely polarised photons. This could provide clear experimental evidence for the chiral-odd GPD E ‾ T . In addition, the existence of a non-negligible contribution of longitudinally polarised photons is suggested by the | t | -dependence of the cross section at x B j < 0.1. Altogether, these results provide valuable input for future modelling of GPDs and thus of cross sections for exclusive pseudo-scalar meson production. Furthermore, they can be expected to facilitate the study of next-to-leading order corrections and higher-twist contributions.Pubblicazioni consigliate
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