APS » Phys. Rev. D » Volume 79 » Issue 1

I. Abt,²⁴ M. Adams,¹¹ M. Agari,¹⁴ H. Albrecht,¹³ A. Aleksandrov,³⁰ V. Amaral,⁹ A. Amorim,⁹ S. J. Aplin,¹³ V. Aushev,¹⁷ Y. Bagaturia,^13,37 V. Balagura,²³ M. Bargiotti,⁶ O. Barsukova,¹² J. Bastos,⁹ J. Batista,⁹ C. Bauer,¹⁴ Th. S. Bauer,¹ A. Belkov,¹² Ar. Belkov,¹² I. Belotelov,¹² A. Bertin,⁶ B. Bobchenko,²³ M. Böcker,²⁷ A. Bogatyrev,²³ G. Bohm,³⁰ M. Bräuer,¹⁴ M. Bruinsma,^29,1 M. Bruschi,⁶ P. Buchholz,²⁷ T. Buran,²⁵ J. Carvalho,⁹ P. Conde,^2,13 C. Cruse,¹¹ M. Dam,¹⁰ K. M. Danielsen,²⁵ M. Danilov,²³ S. De Castro,⁶ H. Deppe,¹⁵ X. Dong,³ H. B. Dreis,¹⁵ V. Egorytchev,¹³ K. Ehret,¹¹ F. Eisele,¹⁵ D. Emeliyanov,¹³ S. Essenov,²³ L. Fabbri,⁶ P. Faccioli,⁶ M. Feuerstack-Raible,¹⁵ J. Flammer,¹³ B. Fominykh,²³ M. Funcke,¹¹ Ll. Garrido,² A. Gellrich,³⁰ B. Giacobbe,⁶ J. Gläß,²¹ D. Goloubkov,^13,34 Y. Golubkov,^13,35 A. Golutvin,²³ I. Golutvin,¹² I. Gorbounov,^13,27 A. Gorišek,¹⁸ O. Gouchtchine,²³ D. C. Goulart,⁸ S. Gradl,¹⁵ W. Gradl,¹⁵ F. Grimaldi,⁶ J. Groth-Jensen,¹⁰ Yu. Guilitsky,^23,36 J. D. Hansen,¹⁰ J. M. Hernández,³⁰ W. Hofmann,¹⁴ M. Hohlmann,¹³ T. Hott,¹⁵ W. Hulsbergen,¹ U. Husemann,²⁷ O. Igonkina,²³ M. Ispiryan,¹⁶ T. Jagla,¹⁴ C. Jiang,³ H. Kapitza,¹³ S. Karabekyan,²⁶ N. Karpenko,¹² S. Keller,²⁷ J. Kessler,¹⁵ F. Khasanov,²³ Yu. Kiryushin,¹² I. Kisel,²⁴ E. Klinkby,¹⁰ K. T. Knöpfle,¹⁴ H. Kolanoski,⁵ S. Korpar,^22,18 C. Krauss,¹⁵ P. Kreuzer,^13,20 P. Križan,^19,18 D. Krücker,⁵ S. Kupper,¹⁸ T. Kvaratskheliia,²³ A. Lanyov,¹² K. Lau,¹⁶ B. Lewendel,¹³ T. Lohse,⁵ B. Lomonosov,^13,33 R. Männer,²¹ R. Mankel,³⁰ S. Masciocchi,¹³ I. Massa,⁶ I. Matchikhilian,²³ G. Medin,⁵ M. Medinnis,¹³ M. Mevius,¹³ A. Michetti,¹³ Yu. Mikhailov,^23,36 R. Mizuk,²³ R. Muresan,¹⁰ M. zur Nedden,⁵ M. Negodaev,^13,33 M. Nörenberg,¹³ S. Nowak,³⁰ M. T. Núñez Pardo de Vera,¹³ M. Ouchrif,^29,1 F. Ould-Saada,²⁵ C. Padilla,¹³ D. Peralta,² R. Pernack,²⁶ R. Pestotnik,¹⁸ B. AA. Petersen,¹⁰ M. Piccinini,⁶ M. A. Pleier,¹⁴ M. Poli,^6,32 V. Popov,²³ D. Pose,^12,15 S. Prystupa,¹⁷ V. Pugatch,¹⁷ Y. Pylypchenko,²⁵ J. Pyrlik,¹⁶ K. Reeves,¹⁴ D. Reßing,¹³ H. Rick,¹⁵ I. Riu,¹³ P. Robmann,³¹ I. Rostovtseva,²³ V. Rybnikov,¹³ F. Sánchez,¹⁴ A. Sbrizzi,¹ M. Schmelling,¹⁴ B. Schmidt,¹³ A. Schreiner,³⁰ H. Schröder,²⁶ U. Schwanke,³⁰ A. J. Schwartz,⁸ A. S. Schwarz,¹³ B. Schwenninger,¹¹ B. Schwingenheuer,¹⁴ F. Sciacca,¹⁴ N. Semprini-Cesari,⁶ S. Shuvalov,^23,5 L. Silva,⁹ L. Sözüer,¹³ S. Solunin,¹² A. Somov,¹³ S. Somov,^13,34 J. Spengler,¹³ R. Spighi,⁶ A. Spiridonov,^30,23 A. Stanovnik,^19,18 M. Starič,¹⁸ C. Stegmann,⁵ H. S. Subramania,¹⁶ M. Symalla,^13,11 I. Tikhomirov,²³ M. Titov,²³ I. Tsakov,²⁸ U. Uwer,¹⁵ C. van Eldik,^13,11 Yu. Vassiliev,¹⁷ M. Villa,⁶ A. Vitale,^6,7 I. Vukotic,^5,30 H. Wahlberg,²⁹ A. H. Walenta,²⁷ M. Walter,³⁰ J. J. Wang,⁴ D. Wegener,¹¹ U. Werthenbach,²⁷ H. Wolters,⁹ R. Wurth,¹³ A. Wurz,²¹ S. Xella-Hansen,¹⁰ Yu. Zaitsev,²³ M. Zavertyaev,^13,14,33 T. Zeuner,^13,27 A. Zhelezov,²³ Z. Zheng,³ R. Zimmermann,²⁶ T. Živko,¹⁸ and A. Zoccoli⁶

(HERA-B Collaboration)

¹NIKHEF, 1009 DB Amsterdam, The Netherlands
²Department ECM, Faculty of Physics, University of Barcelona, E-08028 Barcelona, Spain
³Institute for High Energy Physics, Beijing 100039, P.R. China
⁴Institute of Engineering Physics, Tsinghua University, Beijing 100084, P.R. China
⁵Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany
⁶Dipartimento di Fisica dell' Università di Bologna and INFN Sezione di Bologna, I-40126 Bologna, Italy
⁷Fondazione Giuseppe Occhialini, I-61034 Fossombrone (Pesaro Urbino), Italy
⁸Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA
⁹LIP Coimbra, P-3004-516 Coimbra, Portugal
¹⁰Niels Bohr Institutet, DK 2100 Copenhagen, Denmark
¹¹Institut für Physik, Universität Dortmund, D-44221 Dortmund, Germany
¹²Joint Institute for Nuclear Research Dubna, 141980 Dubna, Moscow, Russia
¹³DESY, D-22603 Hamburg, Germany
¹⁴Max-Planck-Institut für Kernphysik, D-69117 Heidelberg, Germany
¹⁵Physikalisches Institut, Universität Heidelberg, D-69120 Heidelberg, Germany
¹⁶Department of Physics, University of Houston, Houston, Texas 77204, USA
¹⁷Institute for Nuclear Research, Ukrainian Academy of Science, 03680 Kiev, Ukraine
¹⁸J. Stefan Institute, 1001 Ljubljana, Slovenia
¹⁹University of Ljubljana, 1001 Ljubljana, Slovenia
²⁰University of California, Los Angeles, California 90024, USA
²¹Lehrstuhl für Informatik V, Universität Mannheim, D-68131 Mannheim, Germany
²²University of Maribor, 2000 Maribor, Slovenia
²³Institute of Theoretical and Experimental Physics, 117218 Moscow, Russia
²⁴Max-Planck-Institut für Physik, Werner-Heisenberg-Institut, D-80805 München, Germany
²⁵Department of Physics, University of Oslo, N-0316 Oslo, Norway
²⁶Fachbereich Physik, Universität Rostock, D-18051 Rostock, Germany
²⁷Fachbereich Physik, Universität Siegen, D-57068 Siegen, Germany
²⁸INRNE-BAS, Sofia, Bulgaria
²⁹Universiteit Utrecht/NIKHEF, 3584 CB Utrecht, The Netherlands
³⁰DESY, D-15738 Zeuthen, Germany
³¹Physik-Institut, Universität Zürich, CH-8057 Zürich, Switzerland
³²Dipartimento di Energetica dell' Università di Firenze and INFN Sezione di Bologna, Italy
³³P.N. Lebedev Physical Institute, 117924 Moscow B-333, Russia
³⁴Moscow Physical Engineering Institute, 115409 Moscow, Russia
³⁵Moscow State University, 119992 Moscow, Russia
³⁶Institute for High Energy Physics, Protvino, Russia
³⁷High Energy Physics Institute, 380086 Tbilisi, Georgia

A measurement of the ratio R_chic=(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_F^J/psi<0.15 is presented. Both µ⁺µ^- and e⁺e^- J/psi decay channels are observed with an overall statistics of about 15 000 chi_c events, which is by far the largest available sample in pA collisions. The result is R_chic=0.188±0.013_st((+0.024)/(-0.022))_sys averaged over the different materials, when no J/psi and chi_c polarizations are considered. The chi_c1 to chi_c2 production ratio R₁₂=R_chic1/R_chic2 is measured to be 1.02±0.40, leading to a cross section ratio ((sigma(chi[sub c1]))/(sigma(chi[sub c2])))=0.57±0.23. The dependence of R_chic on the Feynman-x of the J/psi, x_F^J/psi, and its transverse momentum, p_T^J/psi, 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_chic and R₁₂ 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_chic could change by a factor between 1.02 and 1.21 and R₁₂ by a factor between 0.89 and 1.16.

©2009 The American Physical Society

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