Detektor crystal ball u MAMI C: ishodi i izgledi

The Crystal Ball/TAPS detector setup provides a hermetic photon and hadron calorimeter for the tagged photon facility at the Mainz Microtron accelerator MAMI. High intensity, polarised photon beams of up to 1.5 GeV are used to study photoinduced reactions on nucleons and nuclei. In this article, an overview of the apparatus and selected recent results is given.Sustav detektora Crystal Ball/TAPS čini zatvoren fotonski i hadronski kalorimetar za istraživanja s označenim fotonima mikrotronskog ubrzivača MAMI u Mainzu. Proučavaju se reakcije izazvane jakim snopovima polariziranih fotona energije do 1.5 GeV na nukleonima i atomskim jezgrama. U radu se opisuje oprema i izbor nedavnih ishoda mjerenja

The Role of Meson Retardation in the NN Interaction above Pion Threshold

A model is developed for the hadronic interaction in the two-nucleon system above pion threshold which is based on meson, nucleon and $\Delta$ degrees of freedom and which includes full meson retardation in the exchange operators. For technical reasons, the model allows maximal one meson to be present explicitly. Thus the Hilbert space contains besides $NN$ and $N\Delta$ also configurations consisting of two nucleons and one meson. For this reason, only two- and three-body unitarity is obeyed, and the model is suited for reactions in the two nucleon sector only, where one pion is produced or absorbed. Starting from a realistic pure nucleonic retarded potential, which had to be renormalized because of the additional $\pi$ and $\Delta$ degrees of freedom, a reasonable fit to experimental $NN$-scattering data could be achieved.Comment: 30 pages revtex including 17 figures, outline of model and discussion shortened, typos correcte

Corrigendum to "Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section" [Phys. Lett. B 793 (2019) 188]

n/

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015

Photoproduction of η and η′ mesons with EtaMAID

The unitary isobar model EtaMAID has been updated with an extended list of nucleon resonances, fitted to recent and new data for differential cross sections and polarization observables. The nonresonant background is described by Regge trajectories of ω,ρ and a1, b1 mesons and in addition Regge cuts, where vector and axial vector mesons are exchanged together with Pomeron and f2 mesons

Photoproduction of

The unitary isobar model EtaMAID has been updated with an extended list of nucleon resonances, fitted to recent and new data for differential cross sections and polarization observables. The nonresonant background is described by Regge trajectories of ω,ρ and a1, b1 mesons and in addition Regge cuts, where vector and axial vector mesons are exchanged together with Pomeron and f2 mesons

Measurement of the cross section for hard exclusive π0 muoproduction on the proton

202We 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.openopenAlexeev M.G.; Alexeev G.D.; Amoroso A.; Andrieux V.; Anfimov N.V.; Anosov V.; Antoshkin A.; Augsten K.; Augustyniak W.; Azevedo C.D.R.; Badelek B.; Balestra F.; Ball M.; Barth J.; Beck R.; Bedfer Y.; Bernhard J.; Bodlak M.; Bordalo P.; Bradamante F.; Bressan A.; Buchele M.; Burtsev V.E.; Chang W.-C.; Chatterjee C.; Chiosso M.; Chumakov A.G.; Chung S.-U.; Cicuttin A.; Crespo M.L.; Dalla Torre S.; Dasgupta S.S.; Dasgupta S.; Denisov O.Y.; Dhara L.; Donskov S.V.; Doshita N.; Dreisbach C.; Dunnweber W.; Dusaev R.R.; Efremov A.; Eversheim P.D.; Faessler M.; Ferrero A.; Finger M.; Fischer H.; Franco C.; du Fresne von Hohenesche N.; Friedrich J.M.; Frolov V.; Fuchey E.; Gautheron F.; Gavrichtchouk O.P.; Gerassimov S.; Giarra J.; Gnesi I.; Gorzellik M.; Grasso A.; Gridin A.; Grosse Perdekamp M.; Grube B.; 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.; Iwata T.; Jandek M.; Jary V.; Joosten R.; Jorg P.; Juraskova K.; Kabuss E.; Kaspar F.; Kerbizi A.; Ketzer B.; Khaustov G.V.; Khokhlov Y.A.; Kisselev Y.; Klein F.; Koivuniemi J.H.; Kolosov V.N.; Kondo Horikawa K.; Konorov I.; Konstantinov V.F.; Kotzinian A.M.; Kouznetsov O.M.; Kral Z.; Kramer M.; Krinner F.; Kroumchtein Z.V.; Kulinich Y.; Kunne F.; Kurek K.; Kurjata R.P.; Kveton A.; Levorato S.; Lian Y.-S.; Lichtenstadt J.; Lin P.-J.; Longo R.; Lyubovitskij V.E.; Maggiora A.; Magnon A.; Makins N.; Makke N.; Mallot G.K.; Mamon S.A.; Marianski B.; Martin A.; Marzec J.; Matousek J.; Matsuda T.; Meshcheryakov G.V.; Meyer M.; Meyer W.; Mikhailov Y.V.; Mikhasenko M.; Mitrofanov E.; Mitrofanov N.; Miyachi Y.; Moretti A.; Naim C.; Nagaytsev A.; Neyret D.; Novy J.; Nowak W.-D.; Nukazuka G.; Nunes A.S.; Olshevsky A.G.; Ostrick M.; Panzieri D.; Parsamyan B.; Paul S.; Peng J.-C.; Pereira F.; Pesek M.; Peshekhonov D.V.; Peskova M.; Pierre N.; Platchkov S.; Pochodzalla J.; Polyakov V.A.; Pretz J.; Quaresma M.; Quintans C.; Ramos S.; Regali C.; Reicherz G.; Riedl C.; Ryabchikov D.I.; Rybnikov A.; Rychter A.; Samoylenko V.D.; Sandacz A.; Sarkar S.; Savin I.A.; Sbrizzai G.; Schmieden H.; Selyunin A.; Silva L.; Sinha L.; Slunecka M.; Smolik J.; Srnka A.; Steffen D.; Stolarski M.; Subrt O.; Sulc M.; Suzuki H.; Szabelski A.; Szameitat T.; Sznajder P.; 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.; Wagner M.; Wallner S.; Wilfert M.; Zaremba K.; Zavada P.; Zavertyaev M.; Zemlyanichkina E.; Zhao Y.; Ziembicki M.Alexeev, M. G.; Alexeev, G. D.; Amoroso, A.; Andrieux, V.; Anfimov, N. V.; Anosov, V.; Antoshkin, A.; Augsten, K.; Augustyniak, W.; Azevedo, C. D. R.; Badelek, B.; Balestra, F.; Ball, M.; Barth, J.; Beck, R.; Bedfer, Y.; Bernhard, J.; Bodlak, M.; Bordalo, P.; Bradamante, F.; Bressan, A.; Buchele, M.; Burtsev, V. E.; Chang, W. -C.; Chatterjee, C.; Chiosso, M.; Chumakov, A. G.; Chung, S. -U.; Cicuttin, A.; Crespo, M. L.; Dalla Torre, S.; Dasgupta, S. S.; Dasgupta, S.; Denisov, O. Y.; Dhara, L.; Donskov, S. V.; Doshita, N.; Dreisbach, C.; Dunnweber, W.; Dusaev, R. R.; Efremov, A.; Eversheim, P. D.; Faessler, M.; Ferrero, A.; Finger, M.; Fischer, H.; Franco, C.; du Fresne von Hohenesche, N.; Friedrich, J. M.; Frolov, V.; Fuchey, E.; Gautheron, F.; Gavrichtchouk, O. P.; Gerassimov, S.; Giarra, J.; Gnesi, I.; Gorzellik, M.; Grasso, A.; Gridin, A.; Grosse Perdekamp, M.; Grube, B.; 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.; Iwata, T.; Jandek, M.; Jary, V.; Joosten, R.; Jorg, P.; Juraskova, K.; Kabuss, E.; Kaspar, F.; Kerbizi, A.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Y. A.; Kisselev, Y.; Klein, F.; Koivuniemi, J. H.; Kolosov, V. N.; Kondo Horikawa, K.; Konorov, I.; Konstantinov, V. F.; Kotzinian, A. M.; Kouznetsov, O. M.; Kral, Z.; Kramer, M.; Krinner, F.; Kroumchtein, Z. V.; Kulinich, Y.; Kunne, F.; Kurek, K.; Kurjata, R. P.; Kveton, A.; Levorato, S.; Lian, Y. -S.; Lichtenstadt, J.; Lin, P. -J.; Longo, R.; Lyubovitskij, V. E.; Maggiora, A.; Magnon, A.; Makins, N.; Makke, N.; Mallot, G. K.; Mamon, S. A.; Marianski, B.; Martin, A.; Marzec, J.; Matousek, J.; Matsuda, T.; Meshcheryakov, G. V.; Meyer, M.; Meyer, W.; Mikhailov, Y. V.; Mikhasenko, M.; Mitrofanov, E.; Mitrofanov, N.; Miyachi, Y.; Moretti, A.; Naim, C.; Nagaytsev, A.; Neyret, D.; Novy, J.; Nowak, W. -D.; Nukazuka, G.; Nunes, A. S.; Olshevsky, A. G.; Ostrick, M.; Panzieri, D.; Parsamyan, B.; Paul, S.; Peng, J. -C.; Pereira, F.; Pesek, M.; Peshekhonov, D. V.; Peskova, M.; Pierre, N.; Platchkov, S.; Pochodzalla, J.; Polyakov, V. A.; Pretz, J.; Quaresma, M.; Quintans, C.; Ramos, S.; Regali, C.; Reicherz, G.; Riedl, C.; Ryabchikov, D. I.; Rybnikov, A.; Rychter, A.; Samoylenko, V. D.; Sandacz, A.; Sarkar, S.; Savin, I. A.; Sbrizzai, G.; Schmieden, H.; Selyunin, A.; Silva, L.; Sinha, L.; Slunecka, M.; Smolik, J.; Srnka, A.; Steffen, D.; Stolarski, M.; Subrt, O.; Sulc, M.; Suzuki, H.; Szabelski, A.; Szameitat, T.; Sznajder, P.; 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.; Wagner, M.; Wallner, S.; Wilfert, M.; Zaremba, K.; Zavada, P.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, Y.; Ziembicki, M