Spin density matrix elements in exclusive ω meson muoproduction

COMPASS Collaboration

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

Spin density matrix elements in exclusive ω meson muoproduction

COMPASS Collaboration

Chair of Physics I

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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 p_T 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.

Original language	English
Article number	126
Journal	European Physical Journal C
Volume	81
Issue number	2
DOIs	https://doi.org/10.1140/epjc/s10052-020-08740-y
State	Published - Feb 2021

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@article{03c1fa0de3bc4b26aabeae51491b0650,

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 S. Paul",

note = "Publisher Copyright: {\textcopyright} 2021, The Author(s).",

year = "2021",

month = feb,

doi = "10.1140/epjc/s10052-020-08740-y",

language = "English",

volume = "81",

journal = "European Physical Journal C",

issn = "1434-6044",

publisher = "Springer Nature",

number = "2",

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TY - JOUR

T1 - Spin density matrix elements in exclusive ω meson muoproduction

AU - COMPASS Collaboration

AU - Alexeev, G. D.

AU - Alexeev, M. G.

AU - Amoroso, A.

AU - Andrieux, V.

AU - Anosov, V.

AU - Antoshkin, A.

AU - Augsten, K.

AU - Augustyniak, W.

AU - Azevedo, C. D.R.

AU - Badełek, B.

AU - Balestra, F.

AU - Ball, M.

AU - Barth, J.

AU - Beck, R.

AU - Bedfer, Y.

AU - Antequera, J. Berenguer

AU - Bernhard, J.

AU - Bodlak, M.

AU - Bradamante, F.

AU - Bressan, A.

AU - Burtsev, V. E.

AU - Chang, W. C.

AU - Chatterjee, C.

AU - Chiosso, M.

AU - Chumakov, A. G.

AU - Chung, S. U.

AU - Cicuttin, A.

AU - Correia, P. M.M.

AU - Crespo, M. L.

AU - D’Ago, D.

AU - Torre, S. Dalla

AU - Dasgupta, S. S.

AU - Dasgupta, S.

AU - Denisenko, I.

AU - Denisov, O. Yu

AU - Donskov, S. V.

AU - Doshita, N.

AU - Dreisbach, Ch

AU - Dünnweber, W.

AU - Dusaev, R. R.

AU - Efremov, A.

AU - Eversheim, P. D.

AU - Faccioli, P.

AU - Faessler, M.

AU - Ferrero, A.

AU - Finger, M.

AU - Fischer, H.

AU - Franco, C.

AU - Paul, S.

PY - 2021/2

Y1 - 2021/2

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85107340629&partnerID=8YFLogxK

U2 - 10.1140/epjc/s10052-020-08740-y

DO - 10.1140/epjc/s10052-020-08740-y

M3 - Article

AN - SCOPUS:85107340629

SN - 1434-6044

VL - 81

JO - European Physical Journal C

JF - European Physical Journal C

IS - 2

M1 - 126

ER -

Spin density matrix elements in exclusive ω meson muoproduction

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