Abstract
We present the first measurement of the timelike Compton scattering process, γp→p^{'}γ^{*}(γ^{*}→e^{+}e^{-}), obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities 2.25<Q^{'2}<9 GeV^{2}, squared momentum transferred 0.1<-t<0.8 GeV^{2}, and average total center-of-mass energy squared s=14.5 GeV^{2}. The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions. The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and thus the D-term in the parametrization of the generalized parton distributions.
Highlights
We present the first measurement of the timelike Compton scattering process, γp → p0γÃðγà → eþe−Þ, obtained with the CLAS12 detector at Jefferson Lab
The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions
The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and the D-term in the parametrization of the generalized parton distributions
Summary
P. Chatagnon ,20,* S. Niccolai,20 S. Stepanyan,36 M. J. Amaryan,29 G. Angelini,12 W. R. Armstrong,1 H. Atac,35 C. Ayerbe Gayoso,44,† N. A. Baltzell,36 L. Barion,13 M. Bashkanov,42 M. Battaglieri,36,15 I. Bedlinskiy,25 F. Benmokhtar,7 A. Bianconi,39,19 L. Biondo,15,18,40 A. S. Biselli,8 M. Bondi,15 F. Bossù,3 S. Boiarinov,36 W. J. Briscoe,12 W. K. Brooks,37,36 D. Bulumulla,29 V. D. Burkert,36 D. S. Carman,36 J. C. Carvajal,10 M. Caudron,20 A. Celentano,15 T. Chetry,24,28 G. Ciullo,13,9 L. Clark,41 P. L. Cole,22 M. Contalbrigo,13 G. Costantini,39,19 V. Crede,11 A. D’Angelo,16,32 N. Dashyan,45 M. Defurne,3 R. De Vita,15 A. Deur,36 S. Diehl,30,5 C. Djalali,28 R. Dupre,20 H. Egiyan,36 M. Ehrhart,20,‡ A. El Alaoui,37 L. El Fassi,24 L. Elouadrhiri,36 S. Fegan,42 R. Fersch,4 A. Filippi,17 G. Gavalian,36 Y. Ghandilyan,45 G. P. Gilfoyle,31 F. X. Girod,36 D. I. Glazier,41 A. A. Golubenko,33 R. W. Gothe,34 Y. Gotra,36 K. A. Griffioen,44 M. Guidal,20 L. Guo,10 H. Hakobyan,37,45 M. Hattawy,29 T. B. Hayward,5,44 D. Heddle,4,36 A. Hobart,20 M. Holtrop,26 C. E. Hyde,29 Y. Ilieva,34 D. G. Ireland,41 E. L. Isupov,33 H. S. Jo,21 K. Joo,5 M. L. Kabir,24 D. Keller,43 G. Khachatryan,45 A. Khanal,10 A. Kim,5 W. Kim,21 A. Kripko,30 V. Kubarovsky,36 S. E. Kuhn,29 L. Lanza,16 M. Leali,39,19 S. Lee,23 P. Lenisa,13,9 K. Livingston,41 I. J. D. MacGregor,41 D. Marchand,20 L. Marsicano,15 V. Mascagna,38,19,§ B. McKinnon,41 C. McLauchlin,34 S. Migliorati,39,19 M. Mirazita,14 V. Mokeev,36 R. A. Montgomery,41 C. Munoz Camacho,20 P. Nadel-Turonski,36 P. Naidoo,41 K. Neupane,34 T. R. O’Connell,5 M. Osipenko,15 M. Ouillon,20 P. Pandey,29 M. Paolone,27,35 L. L. Pappalardo,13,9 R. Paremuzyan,36,26 E. Pasyuk,36 W. Phelps,4,12 O. Pogorelko,25 J. Poudel,29 J. W. Price,2 Y. Prok,29 B. A. Raue,10 T. Reed,10 M. Ripani,15 A. Rizzo,16,32 P. Rossi,36 J. Rowley,28 F. Sabatie,3 A. Schmidt,12 E. P. Segarra,23 Y. G. Sharabian,36 E. V. Shirokov,33 U. Shrestha,5,28 D. Sokhan,3,41 O. Soto,14,37 N. Sparveris,35 I. I. Strakovsky,12 S. Strauch,34 N. Tyler,34 R. Tyson,41 M. Ungaro,36 S. Vallarino,13 L. Venturelli,39,19 H. Voskanyan,45 A. Vossen,6,36 E. Voutier,20 D. P. Watts,42 K. Wei,5 X. Wei,36 R. Wishart,41 B. Yale,44 N. Zachariou,42 J. Zhang,43 and Z. W. Zhao6 10Florida International University, Miami, Florida 33199, USA 11Florida State University, Tallahassee, Florida 32306, USA 12The George Washington University, Washington, D.C. 20052, USA 13INFN, Sezione di Ferrara, 44100 Ferrara, Italy 14INFN, Laboratori Nazionali di Frascati, 00044 Frascati, Italy 15INFN, Sezione di Genova, 16146 Genova, Italy 16INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy 17INFN, Sezione di Torino, 10125 Torino, Italy 18INFN, Sezione di Catania, 95123 Catania, Italy 19INFN, Sezione di Pavia, 27100 Pavia, Italy 20Universite Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France 21Kyungpook National University, Daegu 41566, Republic of Korea 22Lamar University, 4400 M. L. King, Jr. Boulevard, P.O. Box 10046, Beaumont, Texas 77710, USA 23Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA 24Mississippi State University, Mississippi State, Mississippi 39762-5167, USA 25National Research Centre Kurchatov Institute—ITEP, Moscow, 117259, Russia 26University of New Hampshire, Durham, New Hampshire 03824-3568, USA 27New Mexico State University, P.O. Box 30001, Las Cruces, New Mexico 88003, USA 28Ohio University, Athens, Ohio 45701, USA 29Old Dominion University, Norfolk, Virginia 23529, USA 30II Physikalisches Institut der Universitaet Giessen, 35392 Giessen, Germany
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