Transverse Extension of Partons in the Proton probed by Deeply Virtual Compton Scattering
11 Dec 2019 · Akhunzyanov R., Alexeev M. G., Alexeev G. D., Amoroso A., Andrieux V., Anfimov N. V., Anosov V., Antoshkin A., Augsten K., Augustyniak W., Austregesilo A., Azevedo C. D. R., Badelek B., Balestra F., Ball M., Barth J., Beck R., Bedfer Y., Bernhard J., Bicker K., Bielert E. R., Birsa R., Bodlak M., Bordalo P., Bradamante F., Bressan A., Buechele M., Burtin E., Burtsev V. E., Chang W. -C., Chatterjee C., Chiosso M., Choi I., Chumakov A. G., Chung S. -U., Cicuttin A., Crespo M. L., Torre S. Dalla, Dasgupta S. S., Dasgupta S., Denisov O. Yu., Dhara L., Donskov S. V., Doshita N., Dreisbach Ch., Duennweber W., Dusaev R. R., Dziewiecki M., Efremov A., Eversheim P. D., Faessler M., Ferrero A., Finger M., Finger M. jr., Fischer H., Franco C., von Hohenesche N. du Fresne, Friedrich J. M., Frolov V., Fuchey E., Gautheron F., Gavrichtchouk O. P., Gerassimov S., Giarra J., Gnesi I., Gorzellik M., Grasso A., Gridin A., Perdekamp M. Grosse, Grube B., Grussenmeyer T., Guskov A., Hahne D., Hamar G., von Harrach D., Heitz R., Herrmann F., Horikawa N., d'Hose N., Hsieh C. -Y., Huber S., Ishimoto S., Ivanov A., Ivanshin Yu., Iwata T., Jary V., Joosten R., Joerg P., Juraskova K., Kabuss E., Kerbizi A., Ketzer B., Khaustov G. V., Khokhlov Yu. A., Kisselev Yu., Klein F., Koivuniemi J. H., Kolosov V. N., Kondo K., Konorov I., Konstantinov V. F., Kotzinian A. M., Kouznetsov O. M., Kral Z., Kraemer M., Krinner F., Kroumchtein Z. V., Kulinich Y., Kunne F., Kurek K., Kurjata R. P., Kuznetsov I. I., Kveton A., Lednev A. A., Levchenko E. A., Levillain M., Levorato S., Lian Y. -S., Lichtenstadt J., Longo R., Lyubovitskij V. E., Maggiora A., Magnon A., Makins N., Makke N., Mallot G. K., Mamon S. A., Marchand C., Marianski B., Martin A., Marzec J., Matousek J., Matsuda H., Matsuda T., Meshcheryakov G. V., Meyer M., Meyer W., Mikhailov Yu. V., Mikhasenko M., Mitrofanov E., Mitrofanov N., Miyachi Y., Moretti A., Nagaytsev A., Nerling F., Neyret D., Novy J., Nowak W. -D., Nukazuka G., Nunes A. S., Olshevsky A. G., Orlov I., Ostrick M., Panzieri D., Parsamyan B., Paul S., Peng J. -C., Pereira F., Pesaro G., Pesek M., Peskova M., Peshekhonov D. V., Pierre N., Platchkov S., Pochodzalla J., Polyakov V. A., Pretz J., Quaresma M., Quintans C., Ramos S., Regali C., Reicherz G., Riedl C., Rogacheva N. S., Ryabchikov D. I., Rybnikov A., Rychter A., Salac R., Samoylenko V. D., Sandacz A., Santos C., Sarkar S., Savin I. A., Sawada T., Sbrizzai G., Schiavon P., Schmieden H., Schoennig K., Seder E., Selyunin A., Silva L., Sinha L., Sirtl S., Slunecka M., Smolik J., Srnka A., Steffen D., Stolarski M., Subrt O., Sulc M., Suzuki H., Szabelski A., Szameitat T., Sznajder P., Tasevsky M., Tessaro S., Tessarotto F., Thiel A., Tomsa J., Tosello F., Tskhay V., Uhl S., Vasilishin B. I., Vauth A., Veit B. M., Veloso J., Vidon A., Virius M., Wallner S., Wilfert M., ter Wolbeek J., Zaremba K., Zavada P., Zavertyaev M., Zemlyanichkina E., Zhuravlev N., Ziembicki M. ·
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 $\langle x_{\text{Bj}} \rangle = 0.056$.
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