An event mixing technique for Bose-Einstein correlations of two pions in photoproduction around 1 GeV

Abstract

Abstract:We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.

An Event Mixing Method with Invariant-mass/energy Hierarchy Correspondence cut for Bose--Einstein Correlations in $\pi \pi X$ System

“…Inspired by the idea in Ref. [15] that one pion with relatively higher/lower energy can only be swapped with another pion from another event with relatively higher/lower energy in order to maintain the original kinematical correlations of two pions in the sequential decay reactions γp → π 0 ∆ → π 0 π 0 p, in this work a new mixing constraint, named invariant-mass/energy hierarchy correspondence (IMEHC) cut, is proposed for measuring BEC effects in exclusive reactions with ππX final states.…”

“…In other words, the two bosons being swapped should be equal in invariant mass m(π, X) hierarchy at a time or in energy hierarchy at another time. In the new mixing method, the MMC cut [15] and the energy sum order (ESO) cut [16] are still included in the mixing method. The ESO cut is expressed by the definition min(E (ori,1)…”

“…It is still a challenging work to find appropriate event mixing method to suppress the influence of kinematical correlations arising from global conservation laws and intermediate resonances. In 2016, a mixing technique with two mixing cuts, named missing mass consistency (MMC) cut and pion energy (PE) cut, is proposed for π 0 π 0 BEC measurement in the γp → π 0 π 0 p reaction at incident photon energies E γ around 1 GeV (a non-perturbative QCD region) [15]. The MMC cut that requires the missing mass in the mixed event should be identical to that of the original event, was introduced for the sake of energy momentum conservation in the mixed events.…”

Measuring Intensity Interference in a Low Multiplicity System \(\pi \pi X\) with a New Observing Method

“…The new event mixing method is composed of two constraints. The MMC cut [30] is still included in the mixing method, which requires |m mix X − m ori X | < M cut , where M cut is the cut window, and m mix X and m ori X are the missing particle mass for the mixed event and that for the original event, respectively, in order to force the mixed events to be physically equal to original events and to be located in the allowed phase space region. In addition to the MMC cut, a new constraint, named energy sum range cut (ESR), is introduced.…”

“…In the work of Ref. [30] they tried to develop an event mixing method for ππ BEC observations in a three final state system ππX, taking the reaction γp → π 0 π 0 p at incident photon energies around 1 GeV (a non-QCD region) as an example. The effects of kinematical correlations due to energy-momentum conservation was investigated, and an event mixing method which contains two mixing cuts was proposed.…”