Physics Letters B 270 ( 1991 ) 105-I 10 North-Holland PHYSICS LETTERS B and muon-pair cross-sections in proton-nucleus and nucleus-nucleus collisions at 200 GeV per nucleon NA38 Collaboration C. Baglin, A. Baldisseri ~, A. Bussi~re, J.P. Guillaud, R. Kossakowski, P. Liaud, F. Staley Laboratoire d'Annecy-le-Vieux de Physique des Particules, 1N2P3-CNRS, B.P. 110, F- 74941 Annecy-le-Vieux Cedex, France A. Baldit, J. Castor, T. Chambon, A. Devaux, J. Fargeix, X. Felgeyrolles, P. Force, L. Fredj, G. Landaud, F. Vazeille Laboratoire de Physique Corpusculaire de Clerrnont-Ferrand, IN2P3-CNRS et Universitd Blaise Pascal F-63177Aubibre Cedex, France P. Sonderegger CERN. CH-1211 Geneva 23, Switzerland M.C. Abreu 2, p. Bordalo 3, R. Ferreira, J.M. Gago 3, C. Lourengo 4, L. Peralta 2, S. Ramos 3, S. Silva, J. Varela 3 LIP, Av. E. Garcia 14-1, P-IO00 Lisbon, Portugal C. Gerschel, D. Jouan, S. Papillon, X. Tarrago Institut de Physique Nucl~aire, IN2P3-CNRS et Universit~ de Paris-Sud, F-91406 Orsay Cedex, France P. Busson, C. Chariot, B. Chaurand, L. Kluberg, A. Romana, R.A. Salmeron Laboratoire de Physique Nucldaire des Hautes Energies, Ecole Polytechnique, IN2P3-CNRS, F-91128 Palaiseau Cedex, France P. Gorodetzky, B. Grosdidier, C. Racca Centre de Recherches Nucl~aires, IN2P3-CNRS et Universitk Louis Pasteur, B.P. 20, F-6 703 7 Strasbourg Cedex, France R. Cases IFIC, Centro Mixto Universidad de Valencia-CSIC, E-46100 Burjasot, Valencia, Spain M. Alirni 5, M. Bedjidian, D. Contardo, E. Descroix, O. Drapier, J.Y. Grossiord, A. Guichard, R. Haroutunian and J.R. Pizzi Institut de Physique Nucl~aire de Lyon, IN2P3-CNRS et Universitk Claude Bernard, 43, boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France Received 27 June 1991 Muon-pair production has been measured in p-Cu, p--U, O-Cu, O-U and S-U collisions at 200 GeV per nucleon. The cross sections are compatible with the atomic number dependence (Avroj.Atarg.) c~ where a=0.91 ___0.04 for the J/~ resonance and or= 1.01 _+ 0.04 for muon pairs produced in the mass continuum between 1.7 and 2.7 GeV/c 2. 0370-2693/91/$ 03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved. 105