@article{9d3a092a543c4ced8c5a40693b3a4d61,
title = "Spin density matrix elements in exclusive ω meson muoproduction",
abstract = "We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ω meson muoproduction on the proton at COMPASS using 160 GeV/c polarised μ+ and μ- beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/c2< W< 17.0 GeV/c2, with the average kinematics ⟨ Q2⟩ = 2.1 (GeV/c)2, ⟨ W⟩ = 7.6 GeV/c2, and ⟨pT2⟩=0.16 (GeV/c)2. Here, Q2 denotes the virtuality of the exchanged photon, W the mass of the final hadronic system and pT the transverse momentum of the ω 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 (γT∗→VL) 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 ω production.",
author = "{COMPASS Collaboration} and Alexeev, {G. D.} and Alexeev, {M. G.} and A. Amoroso and V. Andrieux and V. Anosov and A. Antoshkin and K. Augsten and W. Augustyniak and Azevedo, {C. D.R.} and B. Bade{\l}ek and F. Balestra and M. Ball and J. Barth and R. Beck and Y. Bedfer and Antequera, {J. Berenguer} and J. Bernhard and M. Bodlak and F. Bradamante and A. Bressan and Burtsev, {V. E.} and Chang, {W. C.} and C. Chatterjee and M. Chiosso and Chumakov, {A. G.} and Chung, {S. U.} and A. Cicuttin and Correia, {P. M.M.} and Crespo, {M. L.} and D. D{\textquoteright}Ago and Torre, {S. Dalla} and Dasgupta, {S. S.} and S. Dasgupta and I. Denisenko and Denisov, {O. Yu} and Donskov, {S. V.} and N. Doshita and Ch Dreisbach and W. D{\"u}nnweber and Dusaev, {R. R.} and A. Efremov and Eversheim, {P. D.} and P. Faccioli and M. Faessler and A. Ferrero and M. Finger and M. Finger and H. Fischer and C. Franco and J. Lichtenstadt",
note = "Publisher Copyright: {\textcopyright} 2021, The Author(s).",
year = "2021",
month = feb,
doi = "10.1140/epjc/s10052-020-08740-y",
language = "אנגלית",
volume = "81",
journal = "European Physical Journal C",
issn = "1434-6044",
publisher = "Springer Nature",
number = "2",
}