Sub-regional event mixing constraints for two-pion Bose–Einstein correlations measurements in ππx system

Abstract

Current BEC measurements in exclusive reactions with very low multiplicities is still a big challenge due to lack of effective observing method. Previously proposed observing approaches using event mixing technique still face problems of sample reduction and introducing extra and unnecessary fitting parameters. Here, we show the viability of a new event mixing approach with sub-regional mixing constraints related to energy hierarchy and energy sum observables. Extensive numerical simulations are performed to test the new mixing technique. Its ability to observe BEC parameters is validated and the systematic bias of the fit BEC parameter [Formula: see text] is improved since this new approach reduces the fitting parameters from 4 to 3 compared to the previously proposed mixing method.