Event-by-event fluctuations of average transverse momentum in central Pb plus Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transve rse momentum of charged particles produced in Pb + Pb collisions at the CER N SPS. This measurement provides previously unavailable information allowin g sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-ev ent average transverse momentum is consistent with independent particle pro duction modified by the known two-particle correlations due to quantum stat istics and final state interactions and folded with the resolution of the N A49 apparatus. For two specific models of non-statistical fluctuations in t ransverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement. (C) 1999 Publish ed by Elsevier Science B.V. All rights reserved.