The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been predicted to cause anomalous fluctuations in the relative production of charged and neutral pions in high-energy hadronic and nuclear collisions. The WA98 experiment has been used to measure charged and photon multiplicities in the central region of 158 AGeV Pb+Pb collisions at the CERN SPS. In a sample of 212646 events, no clear DCC signal can be distinguished. Using a simple DCC model, we have set a 90% C.L. upper limit on the maximum DCC production allowed by the data.
amples of La0.4Bi0.6Mn1−xTixO3 have been prepared and their microstructure, composition, and magnetic properties have been investigated for x = 0.05, 0.1, and 0.5.The deviation in the inverse susceptibility behavior from Curie-Weiss law and increase in susceptibility exponent indicates the evolution of the Griffith's phase in La0.4Bi0.6Mn1−xTixO3 around TC. The presence of Griffith's Phase is inferred due to magnetic frustration with increasing Ti concentration. The deviation between field cooled and zero field cooled magnetization curves is observed in these samples and is attributed to the appearance of the spin glass or cluster glass state that arises due to the magnetic anisotropy.
A high granularity preshower detector has been fabricated and installed in the WA98 Experiment at the CERN SPS for measuring the spatial distribution of photons produced in the forward region in lead ion induced interactions. Photons are counted by detecting the preshower signal in plastic scintillator pads placed behind a 3 radiation length thick lead converter and applying a threshold on the scintillator signal to reject the minimum ionizing particles. Techniques to improve the imaging of the fibre and performance of the detector in the high multiplicity environment of lead-lead collisions are described. Using Monte-Carlo simulation methods and test beam data of π − and e − at various energies the photon counting efficiency is estimated to be 68% for central and 73% for peripheral Pb+Pb collisions. : 24.85.+p, 25.75.-q
PACS
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