Measurement of stopping beam distributions in the PIBETA detector

TL;DR

This paper presents four independent methods to measure beam stopping distributions in the PIBETA detector, crucial for accurate geometrical acceptance calculations, and compares their results for consistency.

Contribution

It introduces and validates four novel approaches for determining beam stopping distributions in a large solid angle detector.

Findings

All four methods yield consistent results.

Beam stopping distributions significantly influence detector acceptance.

The methods improve the precision of geometrical acceptance calculations.

Abstract

Precise calculation of the geometrical acceptance of a large solid angle detector with an integrated stopping target relies on precise knowledge of the beam geometry. We describe four alternative methods that we used to measure the beam stopping distributions in the PIBETA detector active target: (i) light response of segmented target elements to incident beam particles, (ii) back-tracking of charged particles from pi+ and mu+ decays using multi-wire proportional chambers, (iii) volume distribution of the Dalitz decay (pi0->gamma e+e-) event vertices, and (iv) the opening angle distribution of two pi0 photons originating from the beta decay of pi+ at rest. We demonstrate consistent results obtained by these four independent approaches and show how particular beam stopping distributions affect the detector's geometrical acceptance.