Evidence for a pion condensate formation in pp interactions at U-70

TL;DR

This study presents experimental evidence suggesting the formation of a pion condensate in high-multiplicity proton-proton interactions at 50 GeV, indicated by significant fluctuations in neutral pion numbers.

Contribution

It provides the first experimental indication of pion condensate formation in pp interactions through fluctuation analysis of neutral pions at high multiplicity.

Findings

Noticeable growth of neutral pion fluctuations with increasing multiplicity

Fluctuation growth exceeds 7 standard deviations at about 30 pions

Observed fluctuations differ from simulated event predictions

Abstract

A high multiplicity study (project Thermalization, experiment E-190) is carried out on U-70 accelerator at IHEP (Protvino, Russia). This project is aimed at searching for collective phenomena. It is known that pions are mainly produced at the 50 GeV-proton beam accelerator. Their mean energy decreases while multiplicity increasing. Bose-Einstein condensate (BEC) can be formed in this system. The theoretical and experimental studies of BEC have been performed since 70es. Within the framework of an ideal pion gas model M. Gorenstein and V. Begun have shown that sharp growth of fluctuations of the neutral pion number will be a signal of BEC formation with the increase of the total multiplicity (neutral and charged particle sum). SVD-2 Collaboration (JINR, IHEP and SINP MSU) investigated fluctuations of the neutral pion number in pp interactions at 50 GeV/c incident beam on U-70 versus the total multiplicity and has revealed noticeable growth of the scaled variance with the total multiplicity increase. The growth of these fluctuations reaches more than 7 standard deviations for the scaled variance at the total multiplicity about 30 pions as opposed to the tendency for the simulated events. This growth has been observed both in the registered photons and restored neutral pions.