Search for a disoriented chiral condensate signal in particles produced by high-energy heavy ion interactions

Charged particles created by interaction of 200 GeV/nucleon sulfur nuclei with a thin lead target were observed in emulsion plates placed normal to a magnetic field and the beam direction. By measuring the positions of the secondary particle tracks in successive emulsion plates in a magnetic field, momenta and charge-signs of the particles were determined. A new analysis method to search for the existence of periodic charge-sign clusters among the secondary particles emerging from S (200 GeV/nucleon) + Pb collisions was developed and performed using canonical Fourier analysis. The Fourier coefficients reveal sinusoidal wave patterns in the distributions of negative and positive charged particles in pseudorapidity-azimuth (η-&phis;) space, which might be a consequence of disoriented chiral condensate (DCC) in high-energy heavy ion collisions. The possibility of a DCC phase in such interactions has been discussed by a number of theorists. The CERN heavy ion collision experiments, EMU05, EMU09, and EMU16, provide necessary physical quantities for the analysis such as multiplicities, angular distributions, momenta, and charge-signs of secondary particles. A total number of 42 central events were fully measured and analyzed. A few events were found to contain periodic charge-sign clusters in η-&phis; space in the first analysis. A new canonical Fourier analysis method was examined for reliability of signal detection against statistical coincidence. Our current analysis method using 95% confidence level was proven to accept the noise level of 60% in the multiplicity range of EMU05 and EMU09 events and could not show any unique positive evidence for the existence of periodic charge-sign clusters among secondary charged particle distribution beyond the statistical coincidence. This test significantly improves its power of discrimination of signals when the confidence level of detecting one cluster is raised to a 99% confidence level. Possible improvement of the canonical Fourier analysis method and its use is suggested for further study of multi-particle isospin correlation that is theoretically expected by the disoriented chiral condensate model at high energy densities.