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Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

1998; Elsevier BV; Volume: 422; Issue: 1-4 Linguagem: Inglês

10.1016/s0370-2693(98)00083-5

1873-2445

G. Agakichiev, Roland Baur, P. Braun-Munzinger, F. Ceretto, A. Drees, S. Esumi, U. Faschingbauer, Z. Fraenkel, C. Fuchs, E. Gatti, P. Glässel, C. Pérez de los Heros, P. Holl, Ch. Jung, B. Lenkeit, M. Messer, Y. Panebrattsev, A. Pfeiffer, J. Rak, I. Ravinovich, S. V. Razin, P. Řehák, M. Richter, M. Sampietro, N. Saveljić, J. Schukraft, S. Shimansky, W. Seipp, E. Socol, Karsten Specht, J. Stachel, G. Tel-Zur, I. Tserruya, T. Ullrich, Christiane Voigt, Chris J. Benmore, J. P. Wessels, T. Wienold, J.P. Wurm, V. I. Yurevich,

Particle physics theoretical and experimental studies

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 ≤m≤ 2.0 GeV/c2 is enhanced by a factor of 3.5 ± 0.4 (stat) ± 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV/c2. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed p⊥.