Z. Phys. C - Particles and Fields 21, 205-218 (1984) Zeitschriff Partic~ iQr Physik C and Fic:Nds 9 Springer-Verlag 1984 Measurement of the Reaction 77~r~+r~+rc-rc - at PETRA CELLO Collaboration H.-J. Behrend, H. Fenner, M.-J. Schachter 1, V. Schr6der, H. Sindt Deutsches Elektronen-Synchrotron, DESY, D-2000 Hamburg, Federal Republic of Germany O. Achterberg, G. D'Agostini, W.-D. Apel, J. Engler, G. Fliigge, B. Forstbauer, D.C. Fries, W. Fues, K. Gamerdinger, Th. Henkes, G. Hopp, M. Kriiger, H. Kiister, H. Mtiller, H. Randoll 2, G. Schmidt 3, H. Schneider Kernforschungszentrum Karlsruhe and Universitgt Karlsruhe, D-7500 Karlsruhe, Federal Republic of Germany W. de Boer, G. Buschhorn, G. Grindhammer, P. Grosse-Wiesmann, B. Gunderson, C. Kiesling, R. Kotthaus, U. Kruse ~, H. Lierl, D. Liiers, H. Oberlack, P. Schacht Max-Planck-Institut fiir Physik und Astrophysik, D-8000 Miinchen, Federal Republic of Germany G. Bonneaud s, p. Colas, A. Cordier, M. Davier, D. Fournier, J.F. Grivaz, J. Haissinski, V. Journ6, F. Laplanche, F. Le Diberder, U. Mallik 6, E. Ros, J.-J. Veillet Laboratoire de l'Acc616rateur Lin6aire, F-91405 Orsay, France J.H. Field 7, R. George, M. Goldberg, B. Grossetate, O. Hamon, F. Kapusta, F. Kovacs, G. London, R. Pain, L. Poggioli, M. Rivoal Laboratoire de la Physique Nucl~aire et Hautes Energies, Universit6 de Paris, F-75230 Paris, France R. Aleksan, J. Bouchez, G. Carnesecchi, G. Cozzika, Y. Ducros, A. Gaidot, P. Jarry, Y. Lavagne, J. Pamela, J.P. Pansart, F. Pierre Centre d'Etudes Nucl6aires, Saclay, F-91190 Gif-sur-Yvette, France Received 7 September 1983 Abstract. We have determined the cross section for ?,y--~+Tc+~ ~z in a way free of assumptions about the relative contributions from pOpO, p02~ and 4~ (uncorrelated phase space). We find a sharp onset above threshold and a rather high cross section of about 200nb around W~= 1.5 GeV which consists to about 40 % of pOpO production with sizeable con- tributions from p~ and 47c (PS). The total cross section as well as the pOpO content fall rather fast at higher c.m. energies. Attempts to explain this be- 1 Now at SCS, Hamburg, FRG 2 Now at Blaupunkt, Hildesheim, FRG 3 Now at Siemens, Mtinchen, FRG 4 Now at University of Illinois, Urbana, USA 5 Now at CRN Strasbourg, France 6 Now at University of Purdue, Purdue, USA 7 On leave of absence from DESY, Hamburg, FRG haviour in terms of production of known resonances are not successful so far. The angular distributions do not show any significant structure pointing to resonance formation in the 4re-system. Only the pO_ meson is observed in the moment analysis. The de- cay distributions of the pO for forward produced rhos are fairly consistent with helicity conservation of the produced rhos in accordance with the VDM picture. 1. Introduction Since higher energies became available at electron positron colliders (PETRA, PEP), the interest in photon photon collisions has increased considerably.