Measurement of the hard exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:math> muoproduction cross section at COMPASS

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 Q2 ranging from 1 to 8 (GeV/c)2and the Bjorken variable xBj 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 Q2 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 xBj< 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.

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Journal
Physics Letters B
Published
2025-09-04
DOI
https://doi.org/10.1016/j.physletb.2025.139832
Primary Topic
Particle physics theoretical and experimental studies
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article
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article

Measurement of the hard exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:math> muoproduction cross section at COMPASS

A. Thiel, J. Marzec, A. Selyunin, S. Levorato et al.
Physics Letters B
Particle physics theoretical and experimental studies
article

Measurement of the hard exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:math> muoproduction cross section at COMPASS

A. Thiel, J. Marzec, A. Selyunin, S. Levorato, S. Tessaro, Filippo Delcarro, Y. Miyachi, F. Bradamante, K. Lavickova, V. Frolov, A. Rychter, A. Townsend, Y. Bedfer, A. Cicuttin, C. Menezes Pires, N. Doshita, R. Kurjata, B. Parsamyan, M. Hoffmann, О. Денисов, A. Gridin, N. d’Hose, Valery E. Lyubovitskij, S. Paul, J. C. Peng, J. Beckers, W. Florian, F. Tessarotto, A. Bressan, S. Platchkov, I. Konorov, C. Chatterjee, Romina Molina, I. Denisenko, W. Dünnweber, G. D. Alexeev, H. Pekeler, B. Ketzer, B. Ventura, F. Tosello, W. C. Chang, A. Srnka, M. Gorzellik, B. Badełek, A. Kerbizi, Triloki Triloki, G.K. Mallot, P.A. Haas, C. Quintans, C.-Y. Hsieh, Zdeněk Král, D. V. Peshekhonov, D. Eremeev, Daisuke Miura, M.L. Crespo, G. Reicherz, E. Kabuß, A. Martin, S. Ishimoto, M. Grüner, J. Pochodzalla, S.V. Donskov, O. Kouznetsov, S. Wallner, В. Аносов, R. R. Dusaev, J. Lichtenstadt, S. Dasgupta, J. Barth, K.J. Flöthner, J. Nový, G. Sbrizzai, G.V. Khaustov, G. Reicherz, J.F.C.A. Veloso, G. Nukazuka, C.D.R. Azevedo, D. Neyret, F. Kaspar, C. Alice, S. Sarkar, A.M. Kotzinian, B.M Veit, M. Pešková, E. Mitrofanov, S.-U Chung, A. Maltsev, B.M. Veit, W.‐D. Nowak, N. Makke, I. Savin, A. Amoroso, H. Suzuki, F. R. Metzger, R. Joosten, K. Kondo Horikawa, V. A. Polyakov, J. Bernhard, A. Maggiora, A. Nagaytsev, V. N. Kolosov, M. Alexeev, J. Giarra, M. Chiosso, V. D. Samoylenko, Miroslav Virius, S. Gerassimov, D. Spülbeck, D. D’Ago, Yu-Hsiang Lien, T. Matsuda, V. Tskhay, V. D. Samoylenko, V. Andrieux, P. M. M. Correia, M. Zemko, M. Pešek, A. Korzenev, E. Zemlyanichkina, A. Vijayakumar, A. Sandacz, J. Matoušek, Daniel Dall’Igna Ecker, M. Niemiec, Mehran Dehpour, М. Фингер, T. Iwata, A. Olshevskiy, К. Заремба, T. Iwata, L.G. Garcia Ordòñez, A. Guskov, M. Stolarski, M. Ziembicki, D. Giordano, K. Kurek, P. Jörg, D. Panzieri, H. Fischer, S. Dalla Torre, J.H. Koivuniemi, Mathias Wagner, W. Florian, V. Jary, P.-J. Lin, М. Фингер, Ch. Dreisbach, K. Augsten, M. Bodlak, M. Ostrick, M. Große Perdekamp, L. Sinha, M. Šulc, B. Grube, P. Faccioli, M. Faessler, O.P. Gavrichtchouk, Ф. Клейн, W. Meyer, A. Grasso, F. Kunne, P.A. Haas, R. Beck, R. Longo, A. Vidon, O. Kouznetsov, H. Schmieden, W. Augustyniak, D.I. Ryabchikov
article en

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 Q2 ranging from 1 to 8 (GeV/c)2and the Bjorken variable xBj 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 Q2 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 xBj< 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.

Physics Letters BVol. 870
Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), CEA Paris-Saclay (FR), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR)
Openalex Percentile: Top 90%
Particle physics theoretical and experimental studies
DOIOpen Access PDFOpenAlex
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