Search for disoriented chiral condensate at the Fermilab Tevatron

Abstract

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 −p collisions at √ s = 1.8 TeV in the forward direction, ∼ 3.4 < η <∼ 4.2. Data, consisting of 1.3 × 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. I. INTRODUCTIONThe purpose of the MiniMax test/experiment (T-864) at the Fermilab Tevatron as set out in its proposal was to: (1) demonstrate the feasibility of operating spectrometers in the hostile environment of the far-forward, small angle region in high-energy hadron colliders; (2) search for the presence of disoriented chiral condensate (DCC) and possibly related exotic phenomena such as Centauro events; and (3) contribute data on inclusive spectra and multiplicity distributions in an unexplored region of phase space [1,2]. The experiment was proposed in April 1993, commissioned by January 1994, and upgraded in several stages during the next two years. The data reported here were acquired in January 1996.The principal purpose of this paper is to report the results of our DCC search. A signal for the formation and decay of disoriented chiral condensates [3,4] in hadronic and heavy-ion collisions is an anomalous joint multiplicity distribution of neutral and charged secondary pions, reflected in the probability density * Now where f is the fraction of the total number of pions which are neutral. (There are a variety of proposed mechanisms other than DCC which might also lead to this distribution [5]. We will not hereafter explicitly make this distinction.) Note that the distribution Eq. (1) differs markedly from the "generic", binomial partition of pions into charged and neutral species expected from ordinary production mechanisms. Neutral pions were not reconstructed in this experiment. Instead, we studied the joint multiplicity distribution of charged particles and gamma rays. In a recent publication [6], we showed that robust observables can be constructed from such data which still contain much of the information in Eq. (1) regarding the presence (or absence) of DCC. It is this method which we apply to the MiniMax data.The basic detector requirements of a DCC search, then, are to be able to count, event by event, the number of charged particles and photons in a given acceptance. The detailed design of the MiniMax detector was determined by a variety of considerations. The far-forward direction of production angles less than ∼ 50 mrad was chosen because cosmic ray data provide hints of novel phenomena in this region of phase space, and because it is largely unexplored at hadron colliders. In this region it is necessary to determine carefully the production angles of charged particles and the conversion products of photons. We therefore designed a forward spectrometer with a large nu...

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