Search for disoriented chiral condensates in 158 AGeV Pb+Pb collisions

Abstract

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.

Langevin evolution of disoriented chiral condensate

“…Finally, if the transition is a crossover, as is likely at RHIC where µ B is small, and if this crossover is traversed sufficiently quickly that the dynamics can be treated as a "maximally out of equilibrium" quench, then long wavelength oscillations of the chiral condensate are excited to amplitudes which are greatly in excess of those present in equilibrium [10]. The primary signal of these disorientations of the chiral condensate (DCC) is a large number of soft pions exhibiting large fluctuations in isospin [11][12][13][14]10], which have been looked for and not seen in lower energy heavy ion collisions at the CERN SPS [15]. Many other DCC signatures have also been discussed [16].…”

Localized charged-neutral fluctuations in158AGeV Pb+Pb collisions

“…The anti-Centauro events, reported by the JACEE collaboration [9], with large charged-neutral fluctuations are possible candidates for DCC events. The studies carried out so far in p −p [10] and heavy ion [11,12] reactions have searched for fluctuations which extend over a large region of phase space. These measurements have provided upper limits on the presence of DCC-like fluctuations.…”

“…The analysis makes use of a subset of detectors of the WA98 experiment which are used to measure the multiplicities of charged particles and photons. Charged particle hits (N ch ) were counted using a circular Silicon Pad Multiplicity Detector (SPMD) [11] located 32.8 cm downstream from the target. It provided uniform pseudorapidity coverage in the region 2.35 < η < 3.75.…”

“…Strict data selection and cleanup cuts have been applied as described in Ref. [11,14]. After cuts, a total of 85K central events, corresponding to the top 5% of the minimum bias cross section as determined from the measured total transverse energy, have been analyzed.…”

“…[11] has also been used to search for non-statistical fluctuations. The correlation between N γ−like and N ch has been studied in varying φ intervals, by dividing the entire φ-space into 2, 4, 8, and 16 bins.…”