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Observation of the $χ_{c 2} (2 P)$ meson in the reaction $γ γ \to D \bar{D}$ at BABAR

B. Aubert¹, Y. Karyotakis¹, J. P. Lees¹, V. Poireau¹, E. Prencipe¹, X. Prudent¹, V. Tisserand¹, J. Garra Tico², E. Grauges² et al. (BABAR Collaboration)

E. Grauges², M. Martinelli^3a,3b, A. Palano^3a,3b, M. Pappagallo^3a,3b, G. Eigen⁴, B. Stugu⁴, L. Sun⁴, M. Battaglia⁵, D. N. Brown⁵, B. Hooberman⁵, L. T. Kerth⁵, Yu. G. Kolomensky⁵, G. Lynch⁵, I. L. Osipenkov⁵, K. Tackmann⁵, T. Tanabe⁵, C. M. Hawkes⁶, N. Soni⁶, A. T. Watson⁶, H. Koch⁷, T. Schroeder⁷, D. J. Asgeirsson⁸, C. Hearty⁸, T. S. Mattison⁸, J. A. McKenna⁸, M. Barrett⁹, A. Khan⁹, A. Randle-Conde⁹, V. E. Blinov¹⁰, A. D. Bukin^10,*, A. R. Buzykaev¹⁰, V. P. Druzhinin¹⁰, V. B. Golubev¹⁰, A. P. Onuchin¹⁰, S. I. Serednyakov¹⁰, Yu. I. Skovpen¹⁰, E. P. Solodov¹⁰, K. Yu. Todyshev¹⁰, M. Bondioli¹¹, S. Curry¹¹, I. Eschrich¹¹, D. Kirkby¹¹, A. J. Lankford¹¹, P. Lund¹¹, M. Mandelkern¹¹, E. C. Martin¹¹, D. P. Stoker¹¹, H. Atmacan¹², J. W. Gary¹², F. Liu¹², O. Long¹², G. M. Vitug¹², Z. Yasin¹², V. Sharma¹³, C. Campagnari¹⁴, T. M. Hong¹⁴, D. Kovalskyi¹⁴, M. A. Mazur¹⁴, J. D. Richman¹⁴, T. W. Beck¹⁵, A. M. Eisner¹⁵, C. A. Heusch¹⁵, J. Kroseberg¹⁵, W. S. Lockman¹⁵, A. J. Martinez¹⁵, T. Schalk¹⁵, B. A. Schumm¹⁵, A. Seiden¹⁵, L. O. Winstrom¹⁵, C. H. Cheng¹⁶, D. A. Doll¹⁶, B. Echenard¹⁶, F. Fang¹⁶, D. G. Hitlin¹⁶, I. Narsky¹⁶, P. Ongmongkolkul¹⁶, T. Piatenko¹⁶, F. C. Porter¹⁶, R. Andreassen¹⁷, M. S. Dubrovin¹⁷, G. Mancinelli¹⁷, B. T. Meadows¹⁷, K. Mishra¹⁷, M. D. Sokoloff¹⁷, P. C. Bloom¹⁸, W. T. Ford¹⁸, A. Gaz¹⁸, J. F. Hirschauer¹⁸, M. Nagel¹⁸, U. Nauenberg¹⁸, J. G. Smith¹⁸, S. R. Wagner¹⁸, R. Ayad^19,†, W. H. Toki¹⁹, E. Feltresi²⁰, A. Hauke²⁰, H. Jasper²⁰, T. M. Karbach²⁰, J. Merkel²⁰, A. Petzold²⁰, B. Spaan²⁰, K. Wacker²⁰, M. J. Kobel²¹, K. R. Schubert²¹, R. Schwierz²¹, D. Bernard²², E. Latour²², M. Verderi²², P. J. Clark²³, S. Playfer²³, J. E. Watson²³, M. Andreotti^24a,24b, D. Bettoni^24a, C. Bozzi^24a, R. Calabrese^24a,24b, A. Cecchi^24a,24b, G. Cibinetto^24a,24b, E. Fioravanti^24a,24b, P. Franchini^24a,24b, E. Luppi^24a,24b, M. Munerato^24a,24b, M. Negrini^24a,24b, A. Petrella^24a,24b, L. Piemontese^24a, V. Santoro^24a,24b, R. Baldini-Ferroli²⁵, A. Calcaterra²⁵, R. de Sangro²⁵, G. Finocchiaro²⁵, S. Pacetti²⁵, P. Patteri²⁵, I. M. Peruzzi^25,‡, M. Piccolo²⁵, M. Rama²⁵, A. Zallo²⁵, R. Contri^26a,26b, E. Guido^26a,26b, M. Lo Vetere^26a,26b, M. R. Monge^26a,26b, S. Passaggio^26a, C. Patrignani^26a,26b, E. Robutti^26a, S. Tosi^26a,26b, M. Morii²⁷, A. Adametz²⁸, J. Marks²⁸, S. Schenk²⁸, U. Uwer²⁸, F. U. Bernlochner²⁹, H. M. Lacker²⁹, T. Lueck²⁹, A. Volk²⁹, P. D. Dauncey³⁰, M. Tibbetts³⁰, P. K. Behera³¹, M. J. Charles³¹, U. Mallik³¹, C. Chen³², J. Cochran³², H. B. Crawley³², L. Dong³², V. Eyges³², W. T. Meyer³², S. Prell³², E. I. Rosenberg³², A. E. Rubin³², Y. Y. Gao³³, A. V. Gritsan³³, Z. J. Guo³³, N. Arnaud³⁴, M. Davier³⁴, D. Derkach³⁴, J. Firmino da Costa³⁴, G. Grosdidier³⁴, F. Le Diberder³⁴, V. Lepeltier³⁴, A. M. Lutz³⁴, B. Malaescu³⁴, P. Roudeau³⁴, M. H. Schune³⁴, J. Serrano³⁴, V. Sordini^34,§, A. Stocchi³⁴, G. Wormser³⁴, D. J. Lange³⁵, D. M. Wright³⁵, I. Bingham³⁶, J. P. Burke³⁶, C. A. Chavez³⁶, J. R. Fry³⁶, E. Gabathuler³⁶, R. Gamet³⁶, D. E. Hutchcroft³⁶, D. J. Payne³⁶, C. Touramanis³⁶, A. J. Bevan³⁷, C. K. Clarke³⁷, F. Di Lodovico³⁷, R. Sacco³⁷, M. Sigamani³⁷, G. Cowan³⁸, S. Paramesvaran³⁸, A. C. Wren³⁸, D. N. Brown³⁹, C. L. Davis³⁹, A. G. Denig⁴⁰, M. Fritsch⁴⁰, W. Gradl⁴⁰, A. Hafner⁴⁰, K. E. Alwyn⁴¹, D. Bailey⁴¹, R. J. Barlow⁴¹, G. Jackson⁴¹, G. D. Lafferty⁴¹, T. J. West⁴¹, J. I. Yi⁴¹, J. Anderson⁴², A. Jawahery⁴², D. A. Roberts⁴², G. Simi⁴², J. M. Tuggle⁴², C. Dallapiccola⁴³, E. Salvati⁴³, R. Cowan⁴⁴, D. Dujmic⁴⁴, P. H. Fisher⁴⁴, S. W. Henderson⁴⁴, G. Sciolla⁴⁴, M. Spitznagel⁴⁴, R. K. Yamamoto⁴⁴, M. Zhao⁴⁴, P. M. Patel⁴⁵, S. H. Robertson⁴⁵, M. Schram⁴⁵, P. Biassoni^46a,46b, A. Lazzaro^46a,46b, V. Lombardo^46a, F. Palombo^46a,46b, S. Stracka^46a,46b, L. Cremaldi⁴⁷, R. Godang^47,∥, R. Kroeger⁴⁷, P. Sonnek⁴⁷, D. J. Summers⁴⁷, H. W. Zhao⁴⁷, X. Nguyen⁴⁸, M. Simard⁴⁸, P. Taras⁴⁸, H. Nicholson⁴⁹, G. De Nardo^50a,50b, L. Lista^50a, D. Monorchio^50a,50b, G. Onorato^50a,50b, C. Sciacca^50a,50b, G. Raven⁵¹, H. L. Snoek⁵¹, C. P. Jessop⁵², K. J. Knoepfel⁵², J. M. LoSecco⁵², W. F. Wang⁵², L. A. Corwin⁵³, K. Honscheid⁵³, H. Kagan⁵³, R. Kass⁵³, J. P. Morris⁵³, A. M. Rahimi⁵³, S. J. Sekula⁵³, N. L. Blount⁵⁴, J. Brau⁵⁴, R. Frey⁵⁴, O. Igonkina⁵⁴, J. A. Kolb⁵⁴, M. Lu⁵⁴, R. Rahmat⁵⁴, N. B. Sinev⁵⁴, D. Strom⁵⁴, J. Strube⁵⁴, E. Torrence⁵⁴, G. Castelli^55a,55b, N. Gagliardi^55a,55b, M. Margoni^55a,55b, M. Morandin^55a, M. Posocco^55a, M. Rotondo^55a, F. Simonetto^55a,55b, R. Stroili^55a,55b, C. Voci^55a,55b, P. del Amo Sanchez⁵⁶, E. Ben-Haim⁵⁶, G. R. Bonneaud⁵⁶, H. Briand⁵⁶, J. Chauveau⁵⁶, O. Hamon⁵⁶, Ph. Leruste⁵⁶, G. Marchiori⁵⁶, J. Ocariz⁵⁶, A. Perez⁵⁶, J. Prendki⁵⁶, S. Sitt⁵⁶, L. Gladney⁵⁷, M. Biasini^58a,58b, E. Manoni^58a,58b, C. Angelini^59a,59b, G. Batignani^59a,59b, S. Bettarini^59a,59b, G. Calderini^59a,59b,¶, M. Carpinelli^59a,59b,**, A. Cervelli^59a,59b, F. Forti^59a,59b, M. A. Giorgi^59a,59b, A. Lusiani^59a,59c, M. Morganti^59a,59b, N. Neri^59a,59b, E. Paoloni^59a,59b, G. Rizzo^59a,59b, J. J. Walsh^59a, D. Lopes Pegna⁶⁰, C. Lu⁶⁰, J. Olsen⁶⁰, A. J. S. Smith⁶⁰, A. V. Telnov⁶⁰, F. Anulli^61a, E. Baracchini^61a,61b, G. Cavoto^61a, R. Faccini^61a,61b, F. Ferrarotto^61a, F. Ferroni^61a,61b, M. Gaspero^61a,61b, P. D. Jackson^61a, L. Li Gioi^61a, M. A. Mazzoni^61a, S. Morganti^61a, G. Piredda^61a, F. Renga^61a,61b, C. Voena^61a, M. Ebert⁶², T. Hartmann⁶², H. Schröder⁶², R. Waldi⁶², T. Adye⁶³, B. Franek⁶³, E. O. Olaiya⁶³, F. F. Wilson⁶³, S. Emery⁶⁴, L. Esteve⁶⁴, G. Hamel de Monchenault⁶⁴, W. Kozanecki⁶⁴, G. Vasseur⁶⁴, Ch. Yèche⁶⁴, M. Zito⁶⁴, M. T. Allen⁶⁵, D. Aston⁶⁵, D. J. Bard⁶⁵, R. Bartoldus⁶⁵, J. F. Benitez⁶⁵, R. Cenci⁶⁵, J. P. Coleman⁶⁵, M. R. Convery⁶⁵, J. C. Dingfelder⁶⁵, J. Dorfan⁶⁵, G. P. Dubois-Felsmann⁶⁵, W. Dunwoodie⁶⁵, R. C. Field⁶⁵, M. Franco Sevilla⁶⁵, B. G. Fulsom⁶⁵, A. M. Gabareen⁶⁵, M. T. Graham⁶⁵, P. Grenier⁶⁵, C. Hast⁶⁵, W. R. Innes⁶⁵, J. Kaminski⁶⁵, M. H. Kelsey⁶⁵, H. Kim⁶⁵, P. Kim⁶⁵, M. L. Kocian⁶⁵, D. W. G. S. Leith⁶⁵, S. Li⁶⁵, B. Lindquist⁶⁵, S. Luitz⁶⁵, V. Luth⁶⁵, H. L. Lynch⁶⁵, D. B. MacFarlane⁶⁵, H. Marsiske⁶⁵, R. Messner^65,*, D. R. Muller⁶⁵, H. Neal⁶⁵, S. Nelson⁶⁵, C. P. O’Grady⁶⁵, I. Ofte⁶⁵, M. Perl⁶⁵, B. N. Ratcliff⁶⁵, A. Roodman⁶⁵, A. A. Salnikov⁶⁵, R. H. Schindler⁶⁵, J. Schwiening⁶⁵, A. Snyder⁶⁵, D. Su⁶⁵, M. K. Sullivan⁶⁵, K. Suzuki⁶⁵, S. K. Swain⁶⁵, J. M. Thompson⁶⁵, J. Va’vra⁶⁵, A. P. Wagner⁶⁵, M. Weaver⁶⁵, C. A. West⁶⁵, W. J. Wisniewski⁶⁵, M. Wittgen⁶⁵, D. H. Wright⁶⁵, H. W. Wulsin⁶⁵, A. K. Yarritu⁶⁵, C. C. Young⁶⁵, V. Ziegler⁶⁵, X. R. Chen⁶⁶, H. Liu⁶⁶, W. Park⁶⁶, M. V. Purohit⁶⁶, R. M. White⁶⁶, J. R. Wilson⁶⁶, M. Bellis⁶⁷, P. R. Burchat⁶⁷, A. J. Edwards⁶⁷, T. S. Miyashita⁶⁷, S. Ahmed⁶⁸, M. S. Alam⁶⁸, J. A. Ernst⁶⁸, B. Pan⁶⁸, M. A. Saeed⁶⁸, S. B. Zain⁶⁸, A. Soffer⁶⁹, S. M. Spanier⁷⁰, B. J. Wogsland⁷⁰, R. Eckmann⁷¹, J. L. Ritchie⁷¹, A. M. Ruland⁷¹, C. J. Schilling⁷¹, R. F. Schwitters⁷¹, B. C. Wray⁷¹, B. W. Drummond⁷², J. M. Izen⁷², X. C. Lou⁷², F. Bianchi^73a,73b, D. Gamba^73a,73b, M. Pelliccioni^73a,73b, M. Bomben^74a,74b, L. Bosisio^74a,74b, C. Cartaro^74a,74b, G. Della Ricca^74a,74b, L. Lanceri^74a,74b, L. Vitale^74a,74b, V. Azzolini⁷⁵, N. Lopez-March⁷⁵, F. Martinez-Vidal⁷⁵, D. A. Milanes⁷⁵, A. Oyanguren⁷⁵, J. Albert⁷⁶, Sw. Banerjee⁷⁶, B. Bhuyan⁷⁶, H. H. F. Choi⁷⁶, K. Hamano⁷⁶, G. J. King⁷⁶, R. Kowalewski⁷⁶, M. J. Lewczuk⁷⁶, I. M. Nugent⁷⁶, J. M. Roney⁷⁶, R. J. Sobie⁷⁶, T. J. Gershon⁷⁷, P. F. Harrison⁷⁷, J. Ilic⁷⁷, T. E. Latham⁷⁷, G. B. Mohanty⁷⁷, E. M. T. Puccio⁷⁷, H. R. Band⁷⁸, X. Chen⁷⁸, S. Dasu⁷⁸, K. T. Flood⁷⁸, Y. Pan⁷⁸, R. Prepost⁷⁸, C. O. Vuosalo⁷⁸, and S. L. Wu⁷⁸ (BABAR Collaboration)

¹Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Université de Savoie, CNRS/IN2P3, F-74941 Annecy-Le-Vieux, France
²Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
^3aINFN Sezione di Bari, I-70126 Bari, Italy
^3bDipartimento di Fisica, Università di Bari, I-70126 Bari, Italy
⁴University of Bergen, Institute of Physics, N-5007 Bergen, Norway
⁵Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
⁶University of Birmingham, Birmingham, B15 2TT, United Kingdom
⁷Ruhr Universität Bochum, Institut für Experimentalphysik 1, D-44780 Bochum, Germany
⁸University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
⁹Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom
¹⁰Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
¹¹University of California at Irvine, Irvine, California 92697, USA
¹²University of California at Riverside, Riverside, California 92521, USA
¹³University of California at San Diego, La Jolla, California 92093, USA
¹⁴University of California at Santa Barbara, Santa Barbara, California 93106, USA
¹⁵University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA
¹⁶California Institute of Technology, Pasadena, California 91125, USA
¹⁷University of Cincinnati, Cincinnati, Ohio 45221, USA
¹⁸University of Colorado, Boulder, Colorado 80309, USA
¹⁹Colorado State University, Fort Collins, Colorado 80523, USA
²⁰Technische Universität Dortmund, Fakultät Physik, D-44221 Dortmund, Germany
²¹Technische Universität Dresden, Institut für Kern- und Teilchenphysik, D-01062 Dresden, Germany
²²Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, F-91128 Palaiseau, France
²³University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
^24aINFN Sezione di Ferrara, I-44100 Ferrara, Italy
^24bDipartimento di Fisica, Università di Ferrara, I-44100 Ferrara, Italy
²⁵INFN Laboratori Nazionali di Frascati, I-00044 Frascati, Italy
^26aINFN Sezione di Genova, I-16146 Genova, Italy
^26bDipartimento di Fisica, Università di Genova, I-16146 Genova, Italy
²⁷Harvard University, Cambridge, Massachusetts 02138, USA
²⁸Universität Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany
²⁹Humboldt-Universität zu Berlin, Institut für Physik, Newtonstrasse 15, D-12489 Berlin, Germany
³⁰Imperial College London, London, SW7 2AZ, United Kingdom
³¹University of Iowa, Iowa City, Iowa 52242, USA
³²Iowa State University, Ames, Iowa 50011-3160, USA
³³Johns Hopkins University, Baltimore, Maryland 21218, USA
³⁴Laboratoire de l’Accélérateur Linéaire, IN2P3/CNRS et Université Paris-Sud 11, Centre Scientifique d’Orsay, B. P. 34, F-91898 Orsay Cedex, France
³⁵Lawrence Livermore National Laboratory, Livermore, California 94550, USA
³⁶University of Liverpool, Liverpool L69 7ZE, United Kingdom
³⁷Queen Mary, University of London, London, E1 4NS, United Kingdom
³⁸University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom
³⁹University of Louisville, Louisville, Kentucky 40292, USA
⁴⁰Johannes Gutenberg-Universität Mainz, Institut für Kernphysik, D-55099 Mainz, Germany
⁴¹University of Manchester, Manchester M13 9PL, United Kingdom
⁴²University of Maryland, College Park, Maryland 20742, USA
⁴³University of Massachusetts, Amherst, Massachusetts 01003, USA
⁴⁴Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA
⁴⁵McGill University, Montréal, Québec, Canada H3A 2T8
^46aINFN Sezione di Milano, I-20133 Milano, Italy
^46bDipartimento di Fisica, Università di Milano, I-20133 Milano, Italy
⁴⁷University of Mississippi, University, Mississippi 38677, USA
⁴⁸Université de Montréal, Physique des Particules, Montréal, Québec, Canada H3C 3J7
⁴⁹Mount Holyoke College, South Hadley, Massachusetts 01075, USA
^50aINFN Sezione di Napoli, I-80126 Napoli, Italy
^50bDipartimento di Scienze Fisiche, Università di Napoli Federico II, I-80126 Napoli, Italy
⁵¹NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands
⁵²University of Notre Dame, Notre Dame, Indiana 46556, USA
⁵³The Ohio State University, Columbus, Ohio 43210, USA
⁵⁴University of Oregon, Eugene, Oregon 97403, USA
^55aINFN Sezione di Padova, I-35131 Padova, Italy
^55bDipartimento di Fisica, Università di Padova, I-35131 Padova, Italy
⁵⁶Laboratoire de Physique Nucléaire et de Hautes Energies, IN2P3/CNRS, Université Pierre et Marie Curie-Paris6, Université Denis Diderot-Paris7, F-75252 Paris, France
⁵⁷University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
^58aINFN Sezione di Perugia, I-06100 Perugia, Italy
^58bDipartimento di Fisica, Università di Perugia, I-06100 Perugia, Italy
^59aINFN Sezione di Pisa, I-56127 Pisa, Italy
^59bDipartimento di Fisica, Università di Pisa, I-56127 Pisa, Italy
^59cScuola Normale Superiore di Pisa, I-56127 Pisa, Italy
⁶⁰Princeton University, Princeton, New Jersey 08544, USA
^61aINFN Sezione di Roma, I-00185 Roma, Italy
^61bDipartimento di Fisica, Università di Roma La Sapienza, I-00185 Roma, Italy
⁶²Universität Rostock, D-18051 Rostock, Germany
⁶³Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
⁶⁴CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
⁶⁵SLAC National Accelerator Laboratory, Stanford, California 94309 USA
⁶⁶University of South Carolina, Columbia, South Carolina 29208, USA
⁶⁷Stanford University, Stanford, California 94305-4060, USA
⁶⁸State University of New York, Albany, New York 12222, USA
⁶⁹Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
⁷⁰University of Tennessee, Knoxville, Tennessee 37996, USA
⁷¹University of Texas at Austin, Austin, Texas 78712, USA
⁷²University of Texas at Dallas, Richardson, Texas 75083, USA
^73aINFN Sezione di Torino, I-10125 Torino, Italy
^73bDipartimento di Fisica Sperimentale, Università di Torino, I-10125 Torino, Italy
^74aINFN Sezione di Trieste, I-34127 Trieste, Italy
^74bDipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy
⁷⁵IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
⁷⁶University of Victoria, Victoria, British Columbia, Canada V8W 3P6
⁷⁷Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
⁷⁸University of Wisconsin, Madison, Wisconsin 53706, USA

^*Deceased.
^†Present address: Temple University, Philadelphia, PA 19122, USA.
^‡Also at Università di Perugia, Dipartimento di Fisica, Perugia, Italy.
^§Also at Università di Roma La Sapienza, I-00185 Roma, Italy.
^∥Present address: University of South Alabama, Mobile, AL 36688, USA.
^¶Also at Laboratoire de Physique Nucléaire et de Hautes Energies, IN2P3/CNRS, Université Pierre et Marie Curie-Paris6, Université Denis Diderot-Paris7, F-75252 Paris, France.
^**Also at Università di Sassari, Sassari, Italy.

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Phys. Rev. D 81, 092003 – Published 19 May, 2010

DOI: https://doi.org/10.1103/PhysRevD.81.092003

Abstract

A search for the $Z (3930)$ resonance in $γ γ$ production of the $D \bar{D}$ system has been performed using a data sample corresponding to an integrated luminosity of $384 {fb}^{- 1}$ recorded by the BABAR experiment at the PEP-II asymmetric-energy electron-positron collider. The $D \bar{D}$ invariant mass distribution shows clear evidence of the $Z (3930)$ state with a significance of $5.8 σ$ . We determine mass and width values of $(3926.7 \pm 2.7 \pm 1.1) MeV / c^{2}$ and $(21.3 \pm 6.8 \pm 3.6) MeV$ , respectively. A decay angular analysis provides evidence that the $Z (3930)$ is a tensor state with positive parity and $C$ parity ( $J^{P C} = 2^{++}$ ); therefore we identify the $Z (3930)$ state as the $χ_{c 2} (2 P)$ meson. The value of the partial width $Γ_{γ γ} \times B (Z (3930) \to D \bar{D})$ is found to be $(0.24 \pm 0.05 \pm 0.04) keV$ .