2020 Impact factor 4.590
Particles and Fields
Eur. Phys. J. C 13, 69-78
DOI 10.1007/s100520000288

Low mass dimuon production
in proton and ion induced interactions at the SPS

The NA38 and NA50 Collaborations

M.C. Abreu7,a - B. Alessandro12 - C. Alexa4 - R. Arnaldi12 - J. Astruc9 - M. Atayan14 - C. Baglin2 - A. Baldisseri2 - A. Baldit3 - M. Bedjidian13 - F. Bellaiche13 - S. Beolè12 - V. Boldea4 - P. Bordalo7,b - A. Bussière2 - V. Capony2 - L. Casagrande7 - J. Castor3 - T. Chambon3 - B. Chaurand10 - I. Chevrot3 - B. Cheynis13 - E. Chiavassa12 - C. Cicalò5 - M.P. Comets9 - N. Constans10 - S. Constantinescu4 - D. Contardo13 - A. De Falco5 - G. Dellacasa1 - N. De Marco12 - E. Descroix13,c - A. Devaux3 - S. Dita4 - O. Drapier13 - B. Espagnon3 - J. Fargeix3 - R. Ferreira7 - S.N. Filippov8 - F. Fleuret10 - P. Force3 - M. Gallio12 - Y.K. Gavrilov8 - C. Gerschel9 - P. Giubellino12 - M.B. Golubeva8 - M. Gonin10 - P. Gorodetzky11,d - A.A. Grigorian14 - J.Y. Grossiord13 - F.F. Guber8 - A. Guichard13 - J.P. Guillaud2 - H. Gulkanyan14 - R. Hakobyan14 - R. Haroutunian13 - M. Idzik12,e - D. Jouan9 - T.L. Karavitcheva8 - L. Kluberg10 - R. Kossakowski2 - A.B. Kurepin8 - Y. Le Bornec9 - P. Liaud2 - C. Lourenço6,* - M. Mac Cormick9 - P. Macciotta5 - A. Marzari-Chiesa12 - M. Masera12 - A. Masoni5 - S. Mehrabyan14 - M. Monteno12 - S. Mourgues3 - A. Musso12 - F. Ohlsson-Malek13,f - P. Petiau10 - A. Piccotti12 - J.R. Pizzi13 - F. Prino12 - G. Puddu5 - C. Quintans7 - C. Racca11 - L. Ramello1 - S. Ramos7b - P. Rato-Mendes12 - L. Riccati12 - A. Romana10 - B. Ronceux2 - I. Ropotar6 - P. Saturnini3 - E. Scomparin6,g - S. Serci5 - R. Shahoyan7,h - S. Silva7 - M. Sitta1 - C. Soave12 - P. Sonderegger6,b - F. Staley2 - X. Tarrago9 - N.S. Topilskaya8 - G.L. Usai5 - J. Varela7b,i - E. Vercellin12 - N. Willis9

1Università del Piemonte Orientale, Alessandria and INFN-Torino, Italy
2Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, Annecy-le-Vieux, France
3Laboratoire de Physique Corpusculaire (LPC), Université Blaise Pascal, IN2P3-CNRS, Aubière, France
4Institute of Atomic Physics (IFA), Bucharest, Romania
5Università di Cagliari/INFN, Cagliari, Italy
6CERN, Geneva, Switzerland
7Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Lisbon, Portugal
8Institute for Nuclear Research (INR), Moscow, Russia
9Institut de Physique Nucléaire de Orsay (IPNO), Université Paris-Sud, IN2P3-CNRS, Orsay, France
10Laboratoire de Physique Nucléaire des Hautes Energies (LPNHE), Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
11Centre de Recherches Nucléaires, Université Louis Pasteur, IN2P3-CNRS, Strasbourg, France
12Università di Torino/INFN, Torino, Italy
13Institut de Physique Nucléaire de Lyon (IPNL), Université Claude Bernard, IN2P3-CNRS, Villeurbanne, France
14Yerevan Physics Institute (YerPhI), Yerevan, Armenia
aAlso at UCEH, Universidade do Algarve, Faro, Portugal
bAlso at IST, Universidade Técnica de Lisboa, Lisbon, Portugal
cNow at Université Jean Monnet, Saint-Etienne, France
dNow at PCC Collège de France, Paris, France
eNow at FPNT, University of Mining and Metallurgy, Cracow, Poland
fNow at ISN, University Joseph Fourier and CNRS-IN2P3, Grenoble, France
gNow at Università di Torino/INFN, Torino, Italy
hOn leave of absence from YerPhI, Yerevan, Armenia
iNow at CERN, Geneva, Switzerland
*Corresponding author: Carlos.Lourenco@cern.ch

Received: 14 July 1999 / Revised version: 3 November 1999 /
Published online: 27 January 2000 - © Springer-Verlag 2000

Abstract
The low mass dimuon spectra collected in p-U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The `excess' events have a harder pT distribution than the muon pairs from $\eta$ and $\omega$ Dalitz decays, expected to dominate the mass window 0.4-0.65GeV/c2. We conjecture that the excess events may be due to $q\bar{q}$ annihilations, negligible at low pT but made visible by the mT cut applied in the NA38 data. Taking this assumption to parametrise the p-U spectra, we proceed with the corresponding analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, comparing the measured low mass dimuon spectra with the `expected cocktail'.


Copyright Società Italiana di Fisica, Springer-Verlag 2000