Low-Mass Lepton Pair Production in Pb-Au Collisions at 40 AGeV

Abstract

The CERES/NA45 experiment at the CERN SPS has previously measured $e^{+}{e}^{-}$ pair production in 160 AGeV Pb-Au collisions. In the mass region m>0.2 GeV/c${}^2$, an enhancement of $2.7\pm 0.4(statist.)\pm 0.5(syst.)$ compared to the expectation from known hadronic decay sources was observed. In the 40 AGeV data taken in 1999, an enhancement is again found; a preliminary analysis gives the even larger value of $4.5\pm 1.2(statist.)$. The results are compared to theoretical model calculations based on ${\pi }^{+}{\pi }^{-}$ annihilation with a modified $\rho$-propagator.

arXiv commentTo appear in the proceedings of International Europhysics Conference on High-Energy Physics (HEP 2001), Budapest, Hungary, 12-18 Jul 2001