Spin density matrix elements in exclusive meson muoproduction

G. D. Alexeev; M. G. Alexeev; A. Amoroso; V. Andrieux; V. Anosov; A. Antoshkin; K. Augsten; W. Augustyniak; C. D. R. Azevedo; B. Badełek; F. Balestra; M. Ball; J. Barth; R. Beck; Y. Bedfer; J. Berenguer Antequera; J. Bernhard; M. Bodlak; F. Bradamante; A. Bressan; V. E. Burtsev; W.-C. Chang; C. Chatterjee; M. Chiosso; A. G. Chumakov; S.-U. Chung; A. Cicuttin; P. M. M. Correia; M. L. Crespo; D. D’Ago; S. Dalla Torre; S. S. Dasgupta; S. Dasgupta; I. Denisenko; O. Yu. Denisov; S. V. Donskov; N. Doshita; Ch. Dreisbach; W. Dünnweber; R. R. Dusaev; A. Efremov; P. D. Eversheim; P. Faccioli; M. Faessler; A. Ferrero; M. Finger; M. Finger; H. Fischer; C. Franco; J. M. Friedrich; V. Frolov; F. Gautheron; O. P. Gavrichtchouk; S. Gerassimov; J. Giarra; I. Gnesi; M. Gorzellik; A. Grasso; A. Gridin; M. Grosse Perdekamp; B. Grube; A. Guskov; D. von Harrach; R. Heitz; F. Herrmann; N. Horikawa; N. d’Hose; C.-Y. Hsieh; S. Huber; S. Ishimoto; A. Ivanov; T. Iwata; M. Jandek; V. Jary; P. Jörg; R. Joosten; E. Kabuß; F. Kaspar; A. Kerbizi; B. Ketzer; G. V. Khaustov; Yu. A. Khokhlov; Yu. Kisselev; F. Klein; J. H. Koivuniemi; V. N. Kolosov; K. Kondo Horikawa; I. Konorov; V. F. Konstantinov; A. M. Kotzinian; O. M. Kouznetsov; A. Koval; Z. Kral; F. Krinner; Y. Kulinich; F. Kunne; K. Kurek; R. P. Kurjata; A. Kveton; K. Lavickova; S. Levorato; Y.-S. Lian; J. Lichtenstadt; P.-J. Lin; R. Longo; V. E. Lyubovitskij; A. Maggiora; A. Magnon; N. Makins; N. Makke; G. K. Mallot; A. Maltsev; S. A. Mamon; B. Marianski; A. Martin; J. Marzec; J. Matoušek; T. Matsuda; G. Mattson; G. V. Meshcheryakov; M. Meyer; W. Meyer; Yu. V. Mikhailov; M. Mikhasenko; E. Mitrofanov; N. Mitrofanov; Y. Miyachi; A. Moretti; A. Nagaytsev; C. Naim; D. Neyret; J. Nový; W.-D. Nowak; G. Nukazuka; A. S. Nunes; A. G. Olshevsky; M. Ostrick; D. Panzieri; B. Parsamyan; S. Paul; H. Pekeler; J.-C. Peng; M. Pešek; D. V. Peshekhonov; M. Pešková; N. Pierre; S. Platchkov; J. Pochodzalla; V. A. Polyakov; J. Pretz; M. Quaresma; C. Quintans; C. Regali; G. Reicherz; C. Riedl; T. Rudnicki; D. I. Ryabchikov; A. Rybnikov; A. Rychter; V. D. Samoylenko; A. Sandacz; S. Sarkar; I. A. Savin; G. Sbrizzai; H. Schmieden; A. Selyunin; L. Sinha; M. Slunecka; J. Smolik; A. Srnka; D. Steffen; M. Stolarski; O. Subrt; M. Sulc; H. Suzuki; T. Szameitat; P. Sznajder; S. Tessaro; F. Tessarotto; A. Thiel; J. Tomsa; F. Tosello; A. Townsend; V. Tskhay; S. Uhl; B. I. Vasilishin; A. Vauth; B. M. Veit; J. Veloso; B. Ventura; A. Vidon; M. Virius; M. Wagner; S. Wallner; K. Zaremba; P. Zavada; M. Zavertyaev; M. Zemko; E. Zemlyanichkina; Y. Zhao; M. Ziembicki

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

2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2021) 81: 126
https://doi.org/10.1140/epjc/s10052-020-08740-y

Regular Article – Experimental Physics

Spin density matrix elements in exclusive $ω$ $\omega$ meson muoproduction

G. D. Alexeev⁷, M. G. Alexeev²⁶^,27, A. Amoroso²⁶^,27, V. Andrieux⁹^,28, V. Anosov⁷, A. Antoshkin⁷, K. Augsten⁷^,18, W. Augustyniak²⁹, C. D. R. Azevedo¹, B. Badełek³⁰, F. Balestra²⁶^,27, M. Ball³, J. Barth³, R. Beck³, Y. Bedfer²⁰, J. Berenguer Antequera²⁶^,27, J. Bernhard⁹^,12, M. Bodlak¹⁷, F. Bradamante²⁵, A. Bressan²⁴^,25, V. E. Burtsev²³, W.-C. Chang²¹, C. Chatterjee²⁴^,25, M. Chiosso²⁶^,27, A. G. Chumakov²³, S.-U. Chung¹⁵, A. Cicuttin²⁵, P. M. M. Correia¹, M. L. Crespo²⁵, D. D’Ago²⁴^,25, S. Dalla Torre²⁵, S. S. Dasgupta⁶, S. Dasgupta²⁵, I. Denisenko⁷, O. Yu. Denisov²⁷^an, S. V. Donskov¹⁹, N. Doshita³², Ch. Dreisbach¹⁵, W. Dünnweber¹, R. R. Dusaev²³, A. Efremov⁷, P. D. Eversheim³, P. Faccioli¹¹, M. Faessler¹, A. Ferrero²⁰, M. Finger¹⁷, M. Finger Jr.¹⁷, H. Fischer⁸, C. Franco¹¹, J. M. Friedrich¹⁵, V. Frolov⁷^,9, F. Gautheron²^,28, O. P. Gavrichtchouk⁷, S. Gerassimov¹⁴^,15, J. Giarra¹², I. Gnesi²⁶^,27, M. Gorzellik⁸, A. Grasso²⁶^,27, A. Gridin⁷, M. Grosse Perdekamp²⁸, B. Grube¹⁵, A. Guskov⁷, D. von Harrach¹², R. Heitz²⁸, F. Herrmann⁸, N. Horikawa¹⁶, N. d’Hose²⁰, C.-Y. Hsieh²¹, S. Huber¹⁵, S. Ishimoto³², A. Ivanov⁷, T. Iwata³², M. Jandek¹⁸, V. Jary¹⁸, P. Jörg⁸, R. Joosten³, E. Kabuß¹², F. Kaspar¹⁵, A. Kerbizi²⁴^,25, B. Ketzer³, G. V. Khaustov¹⁹, Yu. A. Khokhlov¹⁹, Yu. Kisselev⁷, F. Klein⁴, J. H. Koivuniemi²^,28, V. N. Kolosov¹⁹, K. Kondo Horikawa³², I. Konorov¹⁴^,15, V. F. Konstantinov¹⁹, A. M. Kotzinian²⁷, O. M. Kouznetsov⁷, A. Koval²⁹, Z. Kral¹⁷, F. Krinner¹⁵, Y. Kulinich²⁸, F. Kunne²⁰, K. Kurek²⁹, R. P. Kurjata³¹, A. Kveton¹⁷, K. Lavickova¹⁸, S. Levorato⁹^,25, Y.-S. Lian²¹, J. Lichtenstadt²², P.-J. Lin²⁰, R. Longo²⁸, V. E. Lyubovitskij²³, A. Maggiora²⁷, A. Magnon¹, N. Makins²⁸, N. Makke²⁵, G. K. Mallot⁸^,9, A. Maltsev⁷, S. A. Mamon²³, B. Marianski²⁹, A. Martin²⁴^,25, J. Marzec³¹, J. Matoušek²⁴^,25, T. Matsuda¹³, G. Mattson²⁸, G. V. Meshcheryakov⁷, M. Meyer²⁰^,28, W. Meyer², Yu. V. Mikhailov¹⁹, M. Mikhasenko³^,9, E. Mitrofanov⁷, N. Mitrofanov⁷, Y. Miyachi³², A. Moretti²⁴^,25, A. Nagaytsev⁷, C. Naim²⁰, D. Neyret²⁰, J. Nový¹⁸, W.-D. Nowak¹², G. Nukazuka³², A. S. Nunes¹¹, A. G. Olshevsky⁷, M. Ostrick¹², D. Panzieri²⁷, B. Parsamyan²⁶^,27, S. Paul¹⁵, H. Pekeler³, J.-C. Peng²⁸, M. Pešek¹⁷, D. V. Peshekhonov⁷, M. Pešková¹⁷, N. Pierre¹²^,20, S. Platchkov²⁰, J. Pochodzalla¹², V. A. Polyakov¹⁹, J. Pretz⁴, M. Quaresma¹¹^,21, C. Quintans¹¹, C. Regali⁸, G. Reicherz², C. Riedl²⁸, T. Rudnicki³⁰, D. I. Ryabchikov¹⁵^,19, A. Rybnikov⁷, A. Rychter³¹, V. D. Samoylenko¹⁹, A. Sandacz²⁹^fz, S. Sarkar⁶, I. A. Savin⁷, G. Sbrizzai²⁴^,25, H. Schmieden⁴, A. Selyunin⁷, L. Sinha⁶, M. Slunecka¹⁷, J. Smolik⁷, A. Srnka⁵, D. Steffen⁹^,15, M. Stolarski¹¹, O. Subrt⁹^,18, M. Sulc¹⁰, H. Suzuki³², T. Szameitat⁸, P. Sznajder²⁹, S. Tessaro²⁵, F. Tessarotto⁹^,25^gu, A. Thiel³, J. Tomsa¹⁷, F. Tosello²⁷, A. Townsend²⁸, V. Tskhay¹⁴, S. Uhl¹⁵, B. I. Vasilishin²³, A. Vauth⁴^,9, B. M. Veit⁹^,12, J. Veloso¹, B. Ventura²⁰, A. Vidon²⁰, M. Virius¹⁸, M. Wagner³, S. Wallner¹⁵, K. Zaremba³¹, P. Zavada⁷, M. Zavertyaev¹⁴, M. Zemko⁹^,18, E. Zemlyanichkina⁷, Y. Zhao²⁵, M. Ziembicki³¹ and COMPASS Collaboration⁹

¹ Department of Physics, University of Aveiro, I3N, 3810-193, Aveiro, Portugal
² Universität Bochum, Institut für Experimentalphysik, 44780, Bochum, Germany
³ Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, 53115, Bonn, Germany
⁴ Universität Bonn, Physikalisches Institut, 53115, Bonn, Germany
⁵ Institute of Scientific Instruments of the CAS, 61264, Brno, Czech Republic
⁶ Matrivani Institute of Experimental Research & Education, 700 030, Calcutta, India
⁷ Joint Institute for Nuclear Research, 141980, Dubna, Moscow region, Russia
⁸ Universität Freiburg, Physikalisches Institut, 79104, Freiburg, Germany
⁹ CERN, 1211, Geneva 23, Switzerland
¹⁰ Technical University in Liberec, 46117, Liberec, Czech Republic
¹¹ LIP, 1649-003, Lisbon, Portugal
¹² Universität Mainz, Institut für Kernphysik, 55099, Mainz, Germany
¹³ University of Miyazaki, 889-2192, Miyazaki, Japan
¹⁴ Lebedev Physical Institute, 119991, Moscow, Russia
¹⁵ Physik Department, Technische Universität München, 85748, Garching, Germany
¹⁶ Nagoya University, 464, Nagoya, Japan
¹⁷ Faculty of Mathematics and Physics, Charles University, 18000, Prague, Czech Republic
¹⁸ Czech Technical University in Prague, 16636, Prague, Czech Republic
¹⁹ State Scientific Center Institute for High Energy Physics of National Research Center ‘Kurchatov Institute’, 142281, Protvino, Russia
²⁰ IRFU, CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
²¹ Academia Sinica, Institute of Physics, 11529, Taipei, Taiwan
²² Tel Aviv University, School of Physics and Astronomy, 69978, Tel Aviv, Israel
²³ Tomsk Polytechnic University, 634050, Tomsk, Russia
²⁴ Department of Physics, University of Trieste, 34127, Trieste, Italy
²⁵ Trieste Section of INFN, 34127, Trieste, Italy
²⁶ Department of Physics, University of Turin, 10125, Turin, Italy
²⁷ Torino Section of INFN, 10125, Turin, Italy
²⁸ Department of Physics, University of Illinois at Urbana-Champaign, IL 61801-3080, Urbana, USA
²⁹ National Centre for Nuclear Research, 02-093, Warsaw, Poland
³⁰ Faculty of Physics, University of Warsaw, 02-093, Warsaw, Poland
³¹ Warsaw University of Technology, Institute of Radioelectronics, 00-665, Warsaw, Poland
³² Yamagata University, 992-8510, Yamagata, Japan

^an Oleg.Denisov@cern.ch
^fz Andrzej.Sandacz@ncbj.gov.pl
^gu Fulvio.Tessarotto@cern.ch

Received: 22 September 2020
Accepted: 7 December 2020
Published online: 5 February 2021

Abstract

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $ω$ $\omega$ meson muoproduction on the proton at COMPASS using 160 GeV/c polarised $μ^{+}$ $\mu ^{+}$ and $μ^{-}$ $\mu ^{-}$ beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/ $c^{2}$ $$c^2$$ $< W <$ $$< W<$$ 17.0 GeV/ $c^{2}$ $$c^2$$ , with the average kinematics $⟨ Q^{2} ⟩ =$ $\langle Q^{2} \rangle =$ 2.1 (GeV/c) $^{2}$ $$^2$$ , $⟨ W ⟩ = 7.6$ $\langle W \rangle = 7.6$ GeV/ $c^{2}$ $$c^2$$ , and $⟨ p_{T}^{2} ⟩ = 0.16$ $\langle p^{2}_{\mathrm{T}} \rangle = 0.16$ (GeV/c) $^{2}$ $$^2$$ . Here, $Q^{2}$ $$Q^2$$ denotes the virtuality of the exchanged photon, W the mass of the final hadronic system and $p_{T}$ $$p_T$$ the transverse momentum of the $ω$ $\omega$ 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 ( $γ_{T}^{*} \to V_{L}$ $\gamma ^*_T \rightarrow V_L$ ) 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 $ω$ $\omega$ production.

This article is dedicated to the memory of Bohdan Marianski.

© The Author(s) 2021

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