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Although the generation of disoriented chiral condensates (DCCs), where the order parameter for chiral symmetry breaking is misaligned with respect to the vacuum direction in isospin state, is quite natural in the theory of strong interactions, they have so far eluded experiments in accelerators and cosmic rays. If DCCs are formed in high-energy nuclear collisions, the relevant outcome are very large event-by-event fluctuations in the neutral-to-charged pion fraction. In this note we search for fingerprints of DCC formation in observables of ultra-high energy cosmic ray showers. We present simulation results for the depth of the maximum ($X_{max}$) and number of muons on the ground, evaluating their sensitivity to the neutral-to-charged pion fraction asymmetry produced in the primary interaction.
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We show that an event-by-event fluctuation of the ratio of neutral pions or resulting photons to charged pions can be used as an effective probe for the formation of disoriented chiral condensates. The fact that the neutral pion fraction produced in case of disoriented chiral condensate formation has a characteristic extended non gaussian shape, is shown to be the key factor which forms the basis of the present analysis.
A new method to search for localized domains of disoriented chiral condensates (DCC) has been proposed by utilising the (eta-phi) phase space distributions of charged particles and photons. Using the discrete wavelet transformation (DWT) analysis technique, it has been found that the presence of DCC domains broadens the distribution of wavelet coefficients in comparison to that of normal events. Strength contours have been derived from the differences in rms deviations of these distributions by taking into account the size of DCC domains and the probability of DCC production in ultra-relativistic heavy ion collisions. This technique can be suitably adopted to experiments measuring multiplicities of charged particles and photons.
We study the dynamics of the chiral phase transition expected during the expansion of the quark-gluon plasma produced in a high energy hadron or heavy ion collision, using the $O(4)$ linear sigma model in the mean field approximation. Imposing boost invariant initial conditions at an initial proper time $tau_0$ and starting from an approximate equilibrium configuration, we investigate the possibility of formation of disoriented chiral condensate during the expansion. In order to create large domains of disoriented chiral condensates low-momentum instabilities have to last for long enough periods of time. Our simulations show no instabilities for an initial thermal configuration. For some of the out-of-equilibrium initial states studied, the fluctuation in the number of particles with low transverse momenta become large at late proper times.
In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an extensive air shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 10^{17} and 10^{19} eV and zenith angles up to 65 degs. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte-Carlo results showing how LTP functions from data are in good agreement with simulations.
We present results from MiniMax (Fermilab T-864), a small test/experiment at the Tevatron designed to search for the production of disoriented chiral condensate (DCC) in $p - bar p$ collisions at $sqrt{s} = 1.8$ TeV in the forward direction, $sim 3.4 < eta < sim 4.2$. Data, consisting of $1.3 times 10^6$ events, are analyzed using the robust observables developed in an earlier paper. The results are consistent with generic, binomial-distribution partition of pions into charged and neutral species. Limits on DCC production in various models are presented.
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