Design and characterization of the POKERINO prototype for the POKER/NA64 experiment at CERN

TL;DR

This paper presents the design, optimization, and experimental characterization of the POKERINO prototype electromagnetic calorimeter, developed for the NA64 experiment at CERN to achieve high energy resolution in dark matter searches.

Contribution

The paper introduces the POKERINO prototype, demonstrating its performance aligns with the requirements for the NA64 experiment's high-energy positron-beam program.

Findings

Achieved energy resolution compatible with experimental requirements

Successfully mitigated SiPM saturation effects at high light levels

Demonstrated stable gain despite beam intensity fluctuations

Abstract

The NA64 experiment at CERN H4 beamline recently started a high-energy positron-beam program to search for light dark matter particles through a thick-target, missing-energy measurement. To fulfil the energy resolution requirement of the physics measurement $\sigma_E/E\simeq2.5\%/\sqrt{E\mathrm{[GeV}]} \oplus 0.5\%$ and cope with the constraints and performance requests of the NA64 setup, a new high-resolution homogeneous electromagnetic calorimeter PKR-CAL has been designed. The detector is based on PbWO$_4$ crystals, each read by multiple SiPM sensors to maximize the light collection. The PKR-CAL design has been optimized to mitigate and control unavoidable SiPM saturation effects at high light levels, as well as to minimize the gain fluctuations induced by instantaneous variations of the H4 beam intensity. The $R\&D$ program culminated in the construction of a small-scale prototype, POKERINO. In this work, we present the results from the experimental characterization campaign of the POKERINO aiming at demonstrating that the obtained performances are compatible with the application requirements.