A prototype large-angle photon veto detector for the P326 experiment at CERN

TL;DR

This paper presents the development and testing of a prototype large-angle photon veto detector using scintillating fibers for the CERN P326 experiment, aiming for high rejection of  decays.

Contribution

It introduces a novel scintillating fiber-based veto detector prototype and evaluates its performance in comparison with tile and lead-glass detectors.

Findings

Fiber prototype achieved good linearity and energy resolution.

Detection efficiency comparable to other detector types.

Prototype meets the requirements for the P326 photon veto system.

Abstract

The P326 experiment at the CERN SPS has been proposed with the purpose of measuring the branching ratio for the decay K^+ \to \pi^+ \nu \bar{\nu} to within 10%. The photon veto system must provide a rejection factor of 10^8 for \pi^0 decays. We have explored two designs for the large-angle veto detectors, one based on scintillating tiles and the other using scintillating fibers. We have constructed a prototype module based on the fiber solution and evaluated its performance using low-energy electron beams from the Frascati Beam-Test Facility. For comparison, we have also tested a tile prototype constructed for the CKM experiment, as well as lead-glass modules from the OPAL electromagnetic barrel calorimeter. We present results on the linearity, energy resolution, and time resolution obtained with the fiber prototype, and compare the detection efficiency for electrons obtained with all three instruments.