An Experimental study of neutral and charged particle fluctuations in Pb Pb collisions at 158-A-GeV

Relativistic quantum field theory treats the vacuum as a medium, with bulk properties characterized by long-range order parameters. This has led to suggestions that regions of disoriented chiral condensate might be formed in high energy colli sion processes. In particular, the approximate chiral symmetry of QCD could lead to regions of vacuum which have chiral order parameters disoriented to directions which have non-zero isospin, i.e. disoriented chiral condensate. The prime accessible signature of DCC is the ratio of neutral to charged pions in a certain range of phase space which should exhibit non-statistical fluctuations. The WA98 experiment has been used to measure the charged and photon multiplicities in the central region of Pb+Pb collisions at the CERN SPS. PMD which has the ability to count photons is positioned at 21.5m from the target, covering the pseudorapidity range 2.9 region as compared to mixed events (I and II) and V+G events. To test the authenticity of the filtered events, these events are passed through various checks. The domains are found to be distributed uniformly in azimuth. The fraction of events having anomalous / values increases with decrease in centrality and increases with decrease in patch size. Search is also made for the ring type DCC formation. No positive evidence has been obtained regarding this search. The results obtained for data are consistent with mixed and V+G events. The top 15-65% of the events are analysed globally in the overlap region of PMD and SPMD. We have found « (0.67+0.04)% events with E? = 50 - 100 GeV and (0.16+0.03)% events with E? — 100 - 150 GeV, having neutral pion fraction, / > 0.70. Some events have been filtered which have shown excess of photons either in small 7y — 4> phase space or in the entire available phase space. It is worth mentioning that these events closely resemble the “anticentauro events” seen by JACEE collaboration in cosmic ray interactions. This is for the first time that anticentauro type events have been observed in heavy ion collisions in an accelerator based experiments