Production of the charmonium states chi_c1 and chi_c2 in proton nucleus interactions at sqrt(s)=41.6 GeV

Abt, I.; Adams, M.; Agari, M.; Albrecht, H.; Alexandrov, A.; Amaral, V.; Amorim, A.; Aplin, S. J.; Aushev, V.; Bagaturia, Y.; Balagura, V.; Bargiotti, M.; Barsukova, O.; Bastos, J.; Batista, J.; Bauer, C.; Bauer, T. S.; Belkov, A.; Belkov, A. R.; Belotelov, I.; Bertin, Antonio; Bobchenko, B.; Boecker, M.; Bogatyrev, A.; Bohm, G.; Brauer, M.; Bruinsma, M.; Bruschi, M.; Buchholz, P.; Buran, T.; Carvalho, J.; Conde, P.; Cruse, C.; Dam, M.; Danielsen, K. M.; Danilov, M.; DE CASTRO, Stefano; Deppe, H.; Dong, X.; Dreis, H. B.; Egorytchev, V.; Ehret, K.; Eisele, F.; Emeliyanov, D.; Essenov, S.; Fabbri, Laura; Faccioli, P.; FEUERSTACK RAIBLE, M.; Flammer, J.; Fominykh, B.; Funcke, M.; Garrido, L.; Gellrich, A.; Giacobbe, B.; Glaess, J.; Goloubkov, D.; Golubkov, Y.; Golutvin, A.; Golutvin, I.; Gorbounov, I.; Gorisek, A.; Gouchtchine, O.; Goulart, D. C.; Gradl, S.; Gradl, W.; Grimaldi, F.; GROTH JENSEN, J.; Guilitsky, Y. U.; Hansen, J. D.; Hernandez, J. M.; Hofmann, W.; Hohlmann, M.; Hott, T.; Hulsbergen, W.; Husemann, U.; Igonkina, O.; Ispiryan, M.; Jagla, T.; Jiang, C.; Kapitza, H.; Karabekyan, S.; Karpenko, N.; Keller, S.; Kessler, J.; Khasanov, F.; Kiryushin, Y. U.; Kisel, I.; Klinkby, E.; Knoepfle, K. T.; Kolanoski, H.; Korpar, S.; Krauss, C.; Kreuzer, P.; Krizan, P.; Kruecker, D.; Kupper, S.; Kvaratsskheliia, T.; Lanyov, A.; Lau, K.; Lewendel, B.; Lohse, T.; Lomonosov, B.; Maenner, R.; Mankel, R.; Masciocchi, S.; Massa, IGNAZIO GIACOMO; Matchikhilian, I.; Medin, G.; Medinnis, M.; Mevius, M.; Michetti, A.; Mikhailov, Y. U.; Mizuk, R.; Muresan, R.; ZUR NEDDEN, M.; Negodaev, M.; Noerenberg, M.; Nowak, S.; NUNEZ PARDO DE VERA, M. T.; Ouchrif, M.; OULD SAADA, F.; Padilla, C.; Peralta, D.; Pernack, R.; Pestotnik, R.; Petersen, B. A.; Piccinini, Maurizio; Pleier, M. A.; Poli, M.; Popov, V.; Pose, D.; Prystupa, S.; Pugatch, V.; Pylypchenko, Y.; Pyrlik, J.; Reeves, K.; Ressing, D.; Rick, H.; Riu, I.; Robmann, P.; Rostovtseva, I.; Rybnikov, V.; Sanchez, F.; Sbrizzi, Antonio; Schmelling, M.; Schmidt, B.; Schreiner, A.; Schroeder, H.; Schwanke, U.; Schwartz, A. J.; Schwarz, A. S.; Schwenninger, B.; Schwingenheuer, B.; Sciacca, F.; SEMPRINI CESARI, Nicola; Shuvalov, S.; Silva, L.; Sozuer, L.; Solunin, S.; Somov, A.; Somov, S.; Spengler, J.; Spighi, R.; Spiridonov, A.; Stanovnik, A.; Staric, M.; Stegmann, C.; Subramania, H. S.; Symalla, M.; Tikhomirov, I.; Titov, M.; Tsakov, I.; Uwer, U.; VAN ELDIK, C.; Vassiliev, Y. U.; Villa, Mauro; Vitale, Antonio; Vukotic, I.; Wahlberg, H.; Walenta, A. H.; Walter, M.; Wang, J. J.; Wegener, D.; Werthenbach, U.; Wolters, H.; Wurth, R.; Wurz, A.; XELLA HANSEN, S.; Zaitsev, Y. U.; Zavertyaev, M.; Zeuner, T.; Zhelezov, A.; Zheng, Z.; Zimmermann, R.; Zivko, T.; Zoccoli, Antonio

doi:10.1103/PhysRevD.79.012001

A measurement of the ratio R_chi_c=(chi_c-->J/psi+gamma)/J/psi in pC , pTi , and pW interactions at 920 GeV/c ( sqrt(s)=41.6 Gev ) in the Feynman-x range -0.35<x^J/psi_F<0.15 is presented . Both mu^+ mu^- and e^+ e^- J/psi decay channels are observed with an overall statistics of about 15000 chi_c events , which is by far the largest available sample in pA collisions . The result is R_chi_c=0.188+/-0.013^+0.024_st-0.022sys averaged over the different materials , when no J/psi and chi_c polarizations are considered . The chi_c1 to chi_c2 production ratio R_12=R_chi_c1/R_chi_c2 is measured to be 1.02+/- 0.40 , leading to a cross section ratio sigma(chi_c1)/sigma(chi_c2)=0.57+/-0.23 . The dependence of R_chi_c on the Feynman-x of the J/psi , x^J/psi_F , and its transverse momentum , p^J/psi_T , is studied , as well as its dependence on the atomic number , A , of the target . For the first time , an extensive study of possible biases on R_chi_c and R_12 due to the dependence of acceptance on the polarization states of J/psi and chi_c is performed . By varying the polarization parameter , lambda_obs , of all produced J/psi's by two sigma around the value measured by HERA-B , and considering the maximum variation due to the possible chi_c1 and chi_c2 polarizations , it is shown that R_chi_c could change by a factor between 1.02 and R_12 by a factor between 0.89 and 1.16 .

I. ABT , M. ADAMS , M. AGARI , H. ALBRECHT , A. ALEXANDROV , V. AMARAL , et al. (2009). Production of the charmonium states chi_c1 and chi_c2 in proton nucleus interactions at sqrt(s)=41.6 GeV. PHYSICAL REVIEW D, PARTICLES, FIELDS, GRAVITATION, AND COSMOLOGY, d79, 012001-1-012001-18 [10.1103/PhysRevD.79.012001].