Measurement of the cross section for hard exclusive $\pi^0$ muoproduction on the proton

M.G. Alexeev , G.D. Alexeev , A. Amoroso , V. Andrieux , N.V. Anfimov , V. Anosov , A. Antoshkin , K. Augsten , W. Augustyniak , C.D.R. Azevedo , B. Badełek , F. Balestra , M. Ball , J. Barth , R. Beck , Y. Bedfer (1) , J. Bernhard , M. Bodlak , P. Bordalo , F. Bradamante , A. Bressan , M. Büchele , V.E. Burtsev , W.-C. Chang , C. Chatterjee , M. Chiosso , A.G. Chumakov , S.-U. Chung , A. Cicuttin , M.L. Crespo , S. Dalla Torre , S.S. Dasgupta , O.Yu. Denisov , L. Dhara , S.V. Donskov , N. Doshita , Ch. Dreisbach , W. Dünnweber , R.R. Dusaev , A. Efremov , P.D. Eversheim , M. Faessler , A. Ferrero (1) , Michael 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 , 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 , T. Iwata , M. Jandek , V. Jary , R. Joosten , P. Jörg , K. Juraskova , 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 , Z. Kral , M. Krämer , F. Krinner , Z.V. Kroumchtein , Y. Kulinich , F. Kunne (1) , K. Kurek , R.P. Kurjata , A. Kveton , S. Levorato , Y.-S. Lian , J. Lichtenstadt , P.-J. Lin (1) , 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 , T. Matsuda , G.V. Meshcheryakov , M. Meyer (1) , W. Meyer , Yu.V. Mikhailov , M. Mikhasenko , E. Mitrofanov , N. Mitrofanov , Y. Miyachi , A. Moretti , C. Naim (1) , A. Nagaytsev , D. Neyret (1) , J. Nový , W.-D. Nowak , G. Nukazuka , A.S. Nunes , A.G. Olshevsky , M. Ostrick , D. Panzieri , B. Parsamyan , S. Paul , J.-C. Peng , F. Pereira , M. Pešek , D.V. Peshekhonov , M. Pešková , 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 , D.I. Ryabchikov , A. Rybnikov , A. Rychter , V.D. Samoylenko , A. Sandacz , S. Sarkar , I.A. Savin , G. Sbrizzai , H. Schmieden , A. Selyunin , L. Silva , L. Sinha , M. Slunecka , J. Smolik , A. Srnka , D. Steffen , M. Stolarski , O. Subrt , M. Sulc , H. Suzuki , A. Szabelski , T. Szameitat , P. Sznajder , 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 , M. Wagner , S. Wallner , M. Wilfert , K. Zaremba , P. Zavada , M. Zavertyaev , E. Zemlyanichkina , Y. Zhao , M. Ziembicki

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

We report on a measurement of hard exclusive π0 muoproduction on the proton by COMPASS using 160 GeV/ c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured μ+ and μ− cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08(GeV/c)2<|t|<0.64(GeV/c)2 . The average kinematics of the measurement are 〈Q2〉=2.0(GeV/c)2 , 〈ν〉=12.8GeV , 〈xBj〉=0.093 and 〈−t〉=0.256(GeV/c)2 . Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2±0.9stat−1.2+1.2|sys)nb/(GeV/c)2 , as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1±1.3stat−0.7+0.7|sys)nb/(GeV/c)2 and (1.5±0.5stat−0.2+0.3|sys)nb/(GeV/c)2 , respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E‾T .

Mots clés: Quantum chromodynamics; Muoproduction; Hard exclusive meson production; Generalised Parton Distributions; experimental results; hydrogen: liquid: target; interference; generalized parton distribution; angular dependence; pi0: leptoproduction; exclusive reaction; muon: beam; cross section: measured; photon: polarization; polarization: transverse; polarization: longitudinal

Domaines: Physique des Hautes Energies - Expérience [hep-ex]

M.G. Alexeev, G.D. Alexeev, A. Amoroso, V. Andrieux, N.V. Anfimov, et al.. Measurement of the cross section for hard exclusive $\pi^0$ muoproduction on the proton. Phys.Lett.B, 2020, 805, pp.135454. ⟨10.1016/j.physletb.2020.135454⟩. ⟨hal-02129556⟩