Physics LettersB 283 (1992) 465-470 PHYSICS LETTERS B North-Holland An observation of exclusive Ac + decays into Z + and mesons ACCMOR Collaboration Amsterdam-Bristol-CERN-Cracow-Munich-Rutherford-Valencia S. Barlag "~, H. Becker "-', A. Bo~ek b, T. B6hringer ,-.3, M. Bosman ", V. Castillo ,,.4 V. Chabaud ", C. Damerell a, C. Daum ~, H. Dietl ~, A. Gillman a, R. Gilmore f, T. Gooch ~, L. G6rlich h, p. Gras ~, Z. Hajduk b, E. Higon g, D.P. Kelsey ,-.5, R. Klanner ,.6, S. Kwan ,..7 B. Lficking ", G. LiJtjens ", G. Lutz a, j. Malos t~ W. Manner ~, E. Neugebauer a.S, H. Palka h M. Pep6 ,~.v, j. Richardson d.~O, K. Rybicki b, H.J. Seebrunner ~, U. Stierlin ~, H.G. Tiecke ~, G. Waltermann ~, S. Watts h, p. Weilhammer ", F. Wickens d, L.W. Wiggers ~, M. Witek b and T. Zeludziewicz b.~m Ma~;-l'lanck-lnstttut )eur Physik, 14-8000 .'~lunich, FRG ~' Institute o['Nuclear Physics. PL-30-055 Cracow, Poland ~" CERN. CH-1211 Geneva 23. Switzerland '~ Rutherford-Appleton Laboratoo', Chilton. Dtdcot OXI 10QX, C'K NIKHEb~II, NL- 1009 DB Amsterdam. The Netherlands r ['ntversJty ~?/'Bristol. BristoIBS8 ITL. UK 8 1t.7(', CSIC and Universtt)" of I "alencta, I "alenc'ia, Spam h Brunel University. U~:hrtdge UB8 3PH. UK Received 25 February 1992 Using data from the NA32 experiment at CERN we have studied the A+ decays containing a 'E ~ among the decay products. The interactions of 230 GeV n- with a Cu target were analysed using a precise vertex telescope (charge-coupled devices and silicon microstrip detectors) and the ACCMOR spectrometer. We have found eleven A, + ~Y*n* n-, one A¢' -..E+K+K-, two Ag ~E÷K+rc - and one Ag .E+n+n - n'a- decays practically without any background. We have measured the branching ratios with respect to the A~ + -.pK- n + channel. ' Present address: KNMI, De Bilt, The Netherlands. ' Present address: Gesamthochschule, W-6600 Saarbr[icken, FRG. ~ Present address: University of Lausanne. CH-1015 Lausanne, Switzerland. "* Present address: IFIC, CSIC and Universit~ of Valencia, Val- encia. Spain. s Present address: Rutherford-Appleton Laboratory, Chilton, Didcot OXI 1 0QX, UK. ~' Present address: DESY, W-2000 Hamburg, FRG. ? Present address: FNAL, Batavia. IL 60510. USA. Present address: Universit~it-GH Siegen, W-5900 Siegen, FRG. '~ Present address: CERN, CH-121 l Geneva 23, Switzerland. "' Present address: University of Geneva, CH-121 I Geneva 04, Switzerland. ~ Present address: University of Melbourne, Melbourne, Victoria. Australia. 1. Introduction Some A~. ~ properties such as its mass and lifetime have already been measured quite precisely. The list of A{ decays is, however, far from complete. In one of our previous papers [ 1 ] we reported on A, + decay modes. Our analysis of single and double charm events led to the determination of branching ratios for fully reconstructed decay modes including those with K ° or A ~ and even for some channels with rt°'s. In the case of A~ + -,Z*X (throughout the paper a particle symbol stands for particle and antiparticle) we are dealing with a special situation. Because of its relatively short lifetime the Z + decays into nTt + or pnO before reaching the first group of our drift chain- 0370-2693/92/$ 05.00 ~3 1992 Elsevier Science Publishers B.V. All rights reserved. 465