Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section

R. Akhunzyanov , M.G. Alexeev , G.D. Alexeev , A. Amoroso , V. Andrieux (1) , N.V. Anfimov , V. Anosov , A. Antoshkin , K. Augsten , W. Augustyniak , A. Austregesilo , C.D.R. Azevedo , B. Badełek , F. Balestra , M. Ball , J. Barth , R. Beck , Y. Bedfer (1) , J. Bernhard , K. Bicker , E.R. Bielert , R. Birsa , M. Bodlak , P. Bordalo , F. Bradamante , A. Bressan , M. Büchele , E. Burtin (1) , V.E. Burtsev , W.-C. Chang , C. Chatterjee , M. Chiosso , I. Choi , A.G. Chumakov , S.-U. Chung , A. Cicuttin , M.L. Crespo , S. Dalla Torre , S.S. Dasgupta , S.S. Dasgupta , O.Yu. Denisov , L. Dhara , S.V. Donskov , N. Doshita , Ch. Dreisbach , W. Dünnweber , R.R. Dusaev , M. Dziewiecki , A. Efremov , P.D. Eversheim , M. Faessler , A. Ferrero (1) , M. Finger , M. Finger , H. Fischer , C. Franco , N. Du Fresne von Hohenesche , J.M. Friedrich , V. Frolov , E. Fuchey (1) , F. Gautheron , O.P. Gavrichtchouk , S. Gerassimov , J. Giarra , I. Gnesi , M. Gorzellik , A. Grasso , A. Gridin , M. Grosse Perdekamp , B. Grube , T. Grussenmeyer , A. Guskov , D. Hahne , G. Hamar , D. von Harrach , R. Heitz , F. Herrmann , N. Horikawa , N. d'Hose (1) , C.-Y. Hsieh , S. Huber , S. Ishimoto , A. Ivanov , Yu. Ivanshin , T. Iwata , V. Jary , R. Joosten , P. Jörg , K. Juraskova , E. Kabuß , A. Kerbizi , B. Ketzer , G.V. Khaustov , Yu.A. Khokhlov , Yu. Kisselev , F. Klein , J.H. Koivuniemi , V.N. Kolosov , K. Kondo , I. Konorov , V.F. Konstantinov , A.M. Kotzinian , O.M. Kouznetsov , Z. Kral , M. Krämer , F. Krinner , Z.V. Kroumchtein , Y. Kulinich , F. Kunne (1) , K. Kurek , R.P. Kurjata , I.I. Kuznetsov , A. Kveton , A.A. Lednev , E.A. Levchenko , M. Levillain (1) , S. Levorato , Y.-S. Lian , J. Lichtenstadt , R. Longo , V.E. Lyubovitskij , A. Maggiora , A. Magnon , N. Makins , N. Makke , G.K. Mallot , S.A. Mamon , B. Marianski , A. Martin , J. Marzec , J. Matoušek , H. Matsuda , T. Matsuda , G.V. Meshcheryakov , M. Meyer (1) , W. Meyer , Yu.V. Mikhailov , M. Mikhasenko , E. Mitrofanov , N. Mitrofanov , Y. Miyachi , A. Moretti , A. Nagaytsev , F. Nerling , D. Neyret (1) , J. Nový , W.-D. Nowak , G. Nukazuka , A.S. Nunes , A.G. Olshevsky , I. Orlov , M. Ostrick , D. Panzieri , B. Parsamyan , S. Paul , J.-C. Peng , F. Pereira , M. Pešek , M. Pešková , D.V. Peshekhonov , N. Pierre (1) , S. Platchkov (1) , J. Pochodzalla , V.A. Polyakov , J. Pretz , M. Quaresma , C. Quintans , S. Ramos , C. Regali , G. Reicherz , C. Riedl , N.S. Rogacheva , D.I. Ryabchikov , A. Rybnikov , A. Rychter , R. Salac , V.D. Samoylenko , A. Sandacz , C. Santos , S. Sarkar , I.A. Savin , T. Sawada , G. Sbrizzai , P. Schiavon , H. Schmieden , K. Schönning , E. Seder (1) , A. Selyunin , L. Silva , L. Sinha , S. Sirtl , M. Slunecka , J. Smolik , A. Srnka , D. Steffen , M. Stolarski , O. Subrt , M. Sulc , H. Suzuki , A. Szabelski , T. Szameitat , P. Sznajder , M. Tasevsky , S. Tessaro , F. Tessarotto , A. Thiel , J. Tomsa , F. Tosello , V. Tskhay , S. Uhl , B.I. Vasilishin , A. Vauth , B.M. Veit , J. Veloso , A. Vidon (1) , M. Virius , S. Wallner , M. Wilfert , J. ter Wolbeek , K. Zaremba , P. Zavada , M. Zavertyaev , E. Zemlyanichkina , N. Zhuravlev , M. Ziembicki

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/$c$ polarized $\mu^+$ and $\mu^-$ beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured $\mu^+$ and $\mu^-$ cross sections for deeply virtual Compton scattering on the squared four-momentum transfer $t$ from the initial to the final final proton. The slope $B$ of the $t$-dependence is fitted with a single exponential function, which yields $B=(4.3 \ \pm \ 0.6_{\text{stat}}\_{- \ 0.3}^{+ \ 0.1}\big\rvert_{\text{sys}}) (\text{GeV}/c)^{-2}$. This result can be converted into an average transverse extension of partons in the proton, $\sqrt{\langle r_{\perp}^2 \rangle} = (0.58 \ \pm \ 0.04_{\text{stat}}\_{- \ 0.02}^{+ \ 0.01}\big\rvert_{\text{sys}})\text{fm}$. For this measurement, the average virtuality of the photon mediating the interaction is $\langle Q^2 \rangle = 1.8\,(\text{GeV/}c)^2$ and the average value of the Bjorken variable is $\langle x_{\text{Bj}} \rangle = 0.056$.

Mots clés: cross section: measured; slope: (calculated); Monte Carlo; momentum transfer dependence; deeply virtual Compton scattering; muon: polarization; 160 GeV/c; size: (transverse); photon: mediation; COMPASS; photon: production; CERN SPS; muon p --> muon p photon; hydrogen: liquid: target; beam: polarization

Domaines: Physique des Hautes Energies - Expérience [hep-ex]; Physique Nucléaire Expérimentale [nucl-ex]

R. Akhunzyanov, M.G. Alexeev, G.D. Alexeev, A. Amoroso, V. Andrieux, et al.. Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section. Phys.Lett.B, 2019, 793, pp.188-194. ⟨10.1016/j.physletb.2019.04.038⟩. ⟨hal-01714262⟩