Measurement of the hard exclusive π 0 muoproduction cross section at COMPASS
Year: 2025
Type: article
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/$c$)$^{\rm\, 2}$ and the Bjorken variable $x_{\rm Bj}$ 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/$c$)$^{\rm\, 2}$ $< |t| <$ 0.64 (GeV/$c$)$^{\rm\, 2}$. 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 polarized photons. This provides clear experimental evidence for the chiral-odd GPD $\overline{E}_T$. In addition, the existence of a non-negligible contribution of longitudinally polarized photons is suggested by the $|t|$-dependence of the cross section at $x_{\rm Bj} < $ 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.
Source: Physics Letters B
Authors: G.D. Alexeev, M.G. Alexeev, C. Alice, A. Amoroso, V. Andrieux, V. Anosov, K. Augsten, W. Augustyniak, C. D R Azevedo, B. Badelek, J. Barth, R. Beck, J. Beckers, Y. Bedfer, J. Bernhard, M. Bodlak, F. Bradamante, A. Bressan, W.-C Chang, C. Chatterjee, M. Chiosso, S.-U Chung, A. Cicuttin, P. M M Correia, M.L. Crespo, D. D’ago, S. Dalla Torre, S.S. Dasgupta, S. Dasgupta, F. Delcarro, I. Denisenko, O. Yu Denisov, M. Dehpour, S.V. Donskov, N. Doshita, Ch Dreisbach, W. Dünnweber, R.R. Dusaev, D. Ecker, D. Eremeev, P. Faccioli, M. Faessler, M. Finger, M. Finger, H. Fischer, K.J. Fl, W. Florian, J.M. Friedrich, V. Frolov, L.G. Garcia Ordòñez, O.P. Gavrichtchouk, S. Gerassimov, J. Giarra, D. Giordano, M. Gorzellik, A. Grasso, A. Gridin, M. Grosse Perdekamp, B. Grube, M. Gr, A. Guskov, P. Haas, D. Von Harrach, M. Hoffmann, N. D’hose, C.-Y Hsieh, S. Ishimoto, A. Ivanov, T. Iwata, V. Jary, R. Joosten, P. Jörg, E. Kabuß, F. Kaspar, A. Kerbizi, B. Ketzer, G.V. Khaustov, F. Klein, J.H. Koivuniemi, V.N. Kolosov, K. Kondo Horikawa, I. Konorov, A. Yu Korzenev, A.M. Kotzinian, O.M. Kouznetsov, A. Koval, Z. Kral, F. Kunne, K. Kurek, R.P. Kurjata, K. Lavickova, S. Levorato, Y.-S Lian, J. Lichtenstadt, P.-J Lin, R. Longo, V.E. Lyubovitskij, A. Maggiora, N. Makke, G.K. Mallot, A. Maltsev, A. Martin, J. Marzec, J. Matoušek, T. Matsuda, C. Menezes Pires, F. Metzger, W. Meyer, M. Mikhasenko, E. Mitrofanov, D. Miura, Y. Miyachi, R. Molina, A. Moretti, A. Nagaytsev, D. Neyret, M. Niemiec, J. Nový, W.-D Nowak, G. Nukazuka, A.G. Olshevsky, M. Ostrick, D. Panzieri, B. Parsamyan, S. Paul, H. Pekeler, J.-C Peng, M. Pešek, D.V. Peshekhonov, M. PeŠková, S. Platchkov, J. Pochodzalla, V.A. Polyakov, C. Quintans, G. Reicherz, C. Riedl, D.I. Ryabchikov, A. Rychter, A. Rymbekova, V.D. Samoylenko, A. Sandacz, S. Sarkar, I.A. Savin, G. Sbrizzai, H. Schmieden, A. Selyunin, L. Sinha, D. Sp, A. Srnka, M. Stolarski, M. Sulc, H. Suzuki, S. Tessaro, F. Tessarotto, A. Thiel, F. Tosello, A. Townsend, T. Triloki, V. Tskhay, B. Valinoti, B.M. Veit, J. F C A Veloso, B. Ventura, A. Vidon, A. Vijayakumar, M. Virius, M. Wagner, S. Wallner, K. Zaremba, M. Zavertyaev, M. Zemko, E. Zemlyanichkina, M. Ziembicki
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Funders: National Science Foundation, Univerzita Karlova v Praze, CERN, Strong, European Commission, Deutsche Forschungsgemeinschaft, Ministry of Education, Culture, Sports, Science and Technology, Ministerstvo Školství, Mládeže a Tělovýchovy, Bundesministerium für Bildung und Forschung, Israel Academy of Sciences and Humanities, Narodowe Centrum Nauki, Forskningsrådet om Hälsa, Arbetsliv och Välfärd, Horizon 2020 Framework Programme, Japan Society for the Promotion of Science, Fundação para a Ciência e a Tecnologia, RIKEN
Awards: Colaboração nas Experiências COMPASS e AMBER do CERN, G14744916, G1574627217, G1935710221, G238070068, G2710527523, G3111662533, G3217029050, The strong interaction at the frontier of knowledge: fundamental research and applications, G3810236772, A Program of Medium Energy Nuclear Physics, G4046065984, The Development of the Polarized Target of COMPASS Spectrometer for the Measurement of Drell-Yan Reaction, G434337789, G4396925471, G4413891503, G497070630, G4974962791, G5148519509, G5886629861, Study of quark-gluon structure of hadrons with a large polarized target, Attention Deficit Hyperactivity Disorder Drugs Use Chronic Effects, Research Infrastructure for experiments at CERN, Getting new knowledge of the microworld using the CERN infrastructure, Study of hadron structure and exotic hadron in the COMPASS experiment, G6997658380, Colaboração nas Experiências COMPASS e AMBER do CERN, G7451223319, G7581181636, Research infrastructure for experiments at CERN, G7799729382, G8113289855, G8140083606, Study on QCD structure of nucleon spin at CERN-COMPASS
OpenAlex ID: W4413983030