Spin density matrix elements in exclusive omega meson muoproduction

Alexeev, Gd; Alexeev, Mg; Amoroso, A; Andrieux, V; Anosov, V; Antoshkin, A; Augsten, K; Augustyniak, W; Azevedo, Cdr; Badelek, B; Balestra, F; Ball, M; Barth, J; Beck, R; Bedfer, Y; Antequera, Jb; Bernhard, J; Bodlak, M; Bradamante, F; Bressan, A; Burtsev, Ve; Chang, Wc; Chatterjee, C; Chiosso, M; Chumakov, Ag; Chung, Su; Cicuttin, A; Correia, Pmm; Crespo, Ml; D'Ago, D; Dalla Torre, S; Dasgupta, Ss; Dasgupta, S; Denisenko, I; Denisov, Oy; Donskov, Sv; Doshita, N; Dreisbach, C; Dunnweber, W; Dusaev, Rr; Efremov, A; Eversheim, Pd; Faccioli, P; Faessler, M; Ferrero, A; Finger, M; Finger, M; Fischer, H; Franco, C; Friedrich, Jm; Frolov, V; Gautheron, F; Gavrichtchouk, Op; Gerassimov, S; Giarra, J; Gnesi, I; Gorzellik, M; Grasso, A; Gridin, A; Perdekamp, Mg; Grube, B; Guskov, A; von Harrach, D; Heitz, R; Herrmann, F; Horikawa, N; Dhose, N; Hsieh, Cy; Huber, S; Ishimoto, S; Ivanov, A; Iwata, T; Jandek, M; Jary, V; Jorg, P; Joosten, R; Kabuss, E; Kaspar, F; Kerbizi, A; Ketzer, B; Khaustov, Gv; Khokhlov, Ya; Kisselev, Y; Klein, F; Koivuniemi, Jh; Kolosov, Vn; Horikawa, Kk; Konorov, I; Konstantinov, Vf; Kotzinian, Am; Kouznetsov, Om; Koval, A; Kral, Z; Krinner, F; Kulinich, Y; Kunne, F; Kurek, K; Kurjata, Rp; Kveton, A; Lavickova, K; Levorato, S; Lian, Ys; Lichtenstadt, J; Lin, Pj; Longo, R; Lyubovitskij, Ve; Maggiora, A; Magnon, A; Makins, N; Makke, N; Mallot, Gk; Maltsev, A; Mamon, Sa; Marianski, B; Martin, A; Marzec, J; Matousek, J; Matsuda, T; Mattson, G; Meshcheryakov, Gv; Meyer, M; Meyer, W; Mikhailov, Yv; Mikhasenko, M; Mitrofanov, E; Mitrofanov, N; Miyachi, Y; Moretti, A; Nagaytsev, A; Naim, C; Neyret, D; Novy, J; Nowak, Wd; Nukazuka, G; Nunes, As; Olshevsky, Ag; Ostrick, M; Panzieri, D; Parsamyan, B; Paul, S; Pekeler, H; Peng, Jc; Pesek, M; Peshekhonov, Dv; Peskova, M; Pierre, N; Platchkov, S; Pochodzalla, J; Polyakov, Va; Pretz, J; Quaresma, M; Quintans, C; Regali, C; Reicherz, G; Riedl, C; Rudnicki, T; Ryabchikov, Di; Rybnikov, A; Rychter, A; Samoylenko, Vd; Sandacz, A; Sarkar, S; Savin, Ia; Sbrizzai, G; Schmieden, H; Selyunin, A; Sinha, L; Slunecka, M; Smolik, J; Srnka, A; Steffen, D; Stolarski, M; Subrt, O; Sulc, M; Suzuki, H; Szameitat, T; Sznajder, P; Tessaro, S; Tessarotto, F; Thiel, A; Tomsa, J; Tosello, F; Townsend, A; Tskhay, V; Uhl, S; Vasilishin, Bi; Vauth, A; Veit, Bm; Veloso, J; Ventura, B; Vidon, A; Virius, M; Wagner, M; Wallner, S; Zaremba, K; Zavada, P; Zavertyaev, M; Zemko, M; Zemlyanichkina, E; Zhao, Y; Ziembicki, M

doi:10.1140/epjc/s10052-020-08740-y

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive omega meson muoproduction on the proton at COMPASS using 160 GeV/c polarised mu(+) and mu(-) beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/c(2) < W < 17.0 GeV/c(2), with the average kinematics < Q(2)>= 2.1 (GeV/c)(2), < W >=7.6 GeV/c(2), and < p(T)(2)>=0.16 (GeV/c)(2). Here, Q(2) denotes the virtuality of the exchanged photon, W the mass of the final hadronic system and p(T) the transverse momentum of the omega 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) -> V-L) indicate a violation of s-channel helicity conservation. Additionally, we observe a sizeable contribution of unnatural-parity-exchange (UPE) transitions that decreases with increasing W. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow to evaluate in a model-dependent way the contribution of UPE transitions and assess the role of parton helicity-flip GPDs in exclusive omega production.