Spin density matrix elements in exclusive $$\rho ^0$$ meson muoproduction

Journal Article · 13 October 2023 · European Physical Journal. C, Particles and Fields (Online)

DOI: https://doi.org/10.1140/epjc/s10052-023-11359-4 · OSTI ID:2336583

Alexeev, G. D. ; Alexeev, M. G. ; Alice, C. ; Amoroso, A. ; Andrieux, V. ; Anosov, V. ; Augsten, K. ; Augustyniak, W.; Azevedo, C. R. ; Badelek, B. ; Barth, J. ; Beck, R.; Bedfer, Y. ; Bernhard, J. ; Bodlak, M.; Bradamante, F. ; Bressan, A. ; Burtsev, V. E.; Chang, W. -C. ; Chatterjee, C. ; Chiosso, M. ; Chumakov, A. G. ; Chung, Suh-urk ^[1]; Cicuttin, A. ; Correia, P. M. ; Crespo, M. L. ; D’Ago, D. ; Torre, S. Dalla ; Dasgupta, S. S. ; Dasgupta, S.; Carro, F. Del ; Denisenko, I. ; Denisov, O. Yu. ; Donskov, S. V. ; Doshita, N. ; Dreisbach, Ch ; Dünnweber, W. ; Dusaev, R. R. ; Ecker, D. ; Efremov, A.; Eremeev, D.; Faccioli, P. ; Faessler, M.; Finger, M. ; Finger, M. ; Fischer, H. ; Flöthner, K. J. ; Florian, W. ; Friedrich, J. M. ; Frolov, V. ; Garcia Ordòñez, L. G. ; Gautheron, F.; Gavrichtchouk, O. P. ; Gerassimov, S. ; Giarra, J. ; Giordano, D. ; Gorzellik, M. ; Grasso, A.; Gridin, A. ; Perdekamp, M. Grosse ; Grube, B. ; Grüner, M. ; Guskov, A. ; Harrach, D. von; Hoffmann, M. ; Horikawa, N.; d’Hose, N. ; Hsieh, C. -Y. ; Huber, S.; Ishimoto, S. ; Ivanov, A.; Iwata, T. ; Jandek, M.; Jary, V. ; Joosten, R. ; Kabuß, E. ; Kaspar, F. ; Kerbizi, A. ; Ketzer, B. ; Khatun, A. ; Khaustov, G. V. ; Klein, F.; Koivuniemi, J. H. ; Kolosov, V. N. ; Horikawa, K. Kondo ; Konorov, I. ; Konstantinov, V. F.; Korzenev, A. M. ; Kotzinian, A. M. ; Kouznetsov, O. M. ; Koval, A.; Kral, Z. ; Krinner, F.; Kunne, F.; Kurek, K. ; Kurjata, R. P. ; Kveton, A. ; Lavickova, K. ; Levorato, S. ; Lian, Y. -S. ; Lichtenstadt, J. ; Lin, P. -J. ; Longo, R. ; Lyubovitskij, V. E. ; Maggiora, A. ; Magnon, A.; Makins, N.; Makke, N. ; Mallot, G. K. ; Maltsev, A. ; Mamon, S. A.; Martin, A. ; Marzec, J. ; Matoušek, J. ; Matsuda, T. ; Mattson, G. ; Pires, C. Menezes ; Metzger, F. ; Meyer, M. ; Meyer, W.; Mikhailov, Yu. V.; Mikhasenko, M. ; Mitrofanov, E.; Miura, D. ; Miyachi, Y. ; Molina, R. ; Moretti, A. ; Nagaytsev, A. ; Naim, C. ; 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. ; Quaresma, M. ; Quintans, C. ; Reicherz, G. ; Riedl, C. ; Ryabchikov, D. I. ; Rychter, A. ; Ryva, A.; Samoylenko, V. D. ; Sandacz, A. ; Sarkar, S. ; Savin, I. A. ; Sbrizzai, G. ; Schmieden, H.; Selyunin, A. ; Sharko, K. ; Sinha, L.; Slunecka, M. ; Spülbeck, D. ; Srnka, A. ; Stolarski, M. ; Subrt, O. ; Sulc, M. ; Suzuki, H. ; Tessaro, S. ; Tessarotto, F. ; Thiel, A. ; Tomsa, J. ; Tosello, F. ; Townsend, A. ; Triloki, T. ; Tskhay, V. ; Valinoti, B. ; Veit, B. M. ; Veloso, J. A. ; Ventura, B.; Virius, M. ; Wagner, M. ; Wallner, S. ; Zaremba, K. ; Zavertyaev, M. ; Zemko, M. ; Zemlyanichkina, E. ; Ziembicki, M.

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1. Brookhaven National Laboratory (BNL), Upton, NY (United States)

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $$\rho ^0$$ meson muoproduction at COMPASS using 160 GeV/c polarised μ⁺ and μ^– beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/c² < W < 17.0 GeV/c², 1.0 (GeV/c)² < $$\mathrm{Q}$$² < 10.0 (GeV/c)² and 0.01 (GeV/c)² < $$p_{\textrm{T}}^2$$ < 0.5 (GeV/c)². Here, W denotes the mass of the final hadronic system, $$\mathrm{Q}$$² the virtuality of the exchanged photon, and $$p_{\textrm{T}}$$ the transverse momentum of the $$\rho ^0$$ meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($$\gamma ^*_T \rightarrow V^{ }_L$$) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive $$\rho ^0$$ production.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: The COMPASS Collaboration
• Grant/Contract Number: SC0012704
• OSTI ID: 2336583
• Report Number(s): BNL--225486-2024-JAAM
• Journal Information: European Physical Journal. C, Particles and Fields (Online), Journal Name: European Physical Journal. C, Particles and Fields (Online) Journal Issue: 10 Vol. 83; ISSN 1434-6052
• Publisher: Springer NatureCopyright Statement
• Country of Publication: United States
• Language: English