2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 13, 433-452
DOI 10.1007/s100520000314

Excess of continuum dimuon production at masses
between threshold and the $J/\Psi$ in S-W interactions
at 200 GeV/c/nucleon

The HELIOS/3 Collaboration

A.L.S. Angelis2 - J. Antos3 - M. Beaulieu4 - H. Beker2 - J. Bystricky8 - M.-G. Catanesi1 - P. Cerello9 - S. Dagan2 - G. Dellacasa9 - S. Di Liberto7 - B. Dolgoshein5 - M. Esten2 - C. W. Fabjan2 - A. Gaidot8 - M. Gallio1 - P. Giubellino9 - U. Goerlach2 - C. Guerra8 - L.-A. Hamel4 - S. Konovalov6 - I. Kralik3 - G. London8 - F. Martelli9 - J.-P. Martin4 - M. Masera9 - M.-A. Mazzoni7 - F. Meddi7 - M.-T. Muciaccia1 - S. Muraviev6 - A. Nomerotsky2 - Y. Oren2 - J.-P. Pansart8 - G. Poulard2 - L. Ramello9 - L. Riccati9 - G. Rosa7 - L. Sandor3 - M. Sarris2 - E. Scomparin9 - A. Shmeleva6 - S. Simone1 - S. Smirnov5 - P. Taras4 - J. Urban3 - E. Vercellin9

1 University of Bari and INFN, Bari, Italy
2 CERN, CH-1211 Geneva, Switzerland
3 Slovak Academy of Sciences, Kosice, Slovak Republic
4 University of Montreal, Montreal, Canada
5 Lebedev Institute of Physics, Moscow, Russia
6 Institute of Physics and Engineering, Moscow, Russia
7 University of Rome "La Sapienza" and INFN Rome Italy
8 DAPNIA, CE-Saclay, Gif/Yvette, France
9 University of Turin and INFN Turin Italy

Received: 7 July 1999 / Revised version: 16 September 1999 /
Published online: 17 February 2000 - © Springer-Verlag 2000

Results are presented on dimuon production for invariant masses ranging from the dimuon threshold up to the $J/\Psi$ meson. Proton-tungsten and sulphur-tungsten interactions at 200 GeV/c/nucleon were measured over a large kinematic region, using the HELIOS/3 dimuon spectrometer at the CERN SPS. In the continuum regions between the dimuon threshold and the $\rho/\omega$ mesons, and between the $\phi$and $J/\Psi$ mesons, an excess is observed in S-W interactions relative to minimum bias p-W interactions. The observed excess is continuous over the explored mass range and has no apparent resonant structure. In the low mass region the dimuon yield increases by $(76\pm 4)$% of the corresponding p-W dimuon spectrum, whereas in the higher mass region the excess amounts to $2.4\pm 0.3$ times the p-W yield. The observed excess for the low mass region follows an exponential transverse mass distribution with an average inverse slope parameter T of $(190\pm5)$MeV/c2, constant for all but the lowest charged multiplicity interval and consistent with the slope of the excess in the higher mass region. In the invariant mass range of 1.35-2.5 GeV/c2 the continuum dimuon mass distribution observed in p-W interactions can be quantitatively understood as a sum of three expected contributions (vector meson decays, semileptonic charm decays and Drell-Yan process), but both in central and in minimum bias S-W interactions an excess is observed with respect to these sources which does not depend on centrality, nor very strongly on the transverse momentum.

Copyright Società Italiana di Fisica, Springer-Verlag 2000