The HIBEAM/NNBAR Calorimeter Prototype

TL;DR

This paper discusses the development of a novel calorimeter prototype for the HIBEAM/NNBAR experiment, aiming to detect neutron oscillations and annihilation events with specialized calorimetry techniques.

Contribution

The paper presents a new calorimeter design using plastic scintillator layers and lead glass for the HIBEAM/NNBAR experiment, including the construction of a prototype for in situ testing.

Findings

Prototype calorimeter being constructed for in situ testing.

Design aims to improve detection of low-energy particles in neutron oscillation experiments.

Plans for installation at an ESS test beam line for background studies.

Abstract

The HIBEAM/NNBAR experiment is a free-neutron search for $n \rightarrow$ sterile $n$ and $n \rightarrow \bar{n}$ oscillations planned to be installed at the European Spallation Source under construction in Lund, Sweden. A key component in the experiment is the detector to identify $n-\bar{n}$ annihilation events, which will produce on average four pions with a final state invariant mass of two nucleons, around $1.9\,$GeV. The beamline and experiment are shielded from magnetic fields which would suppress $n \rightarrow \bar{n}$ transitions, thus no momentum measurement will be possible. Additionally, calorimetry for particles with kinetic energies below $600\,$MeV is challenging, as traditional sampling calorimeters used in HEP would suffer from poor shower statistics. A design study is underway to use a novel approach of a hadronic range measurement in multiple plastic scintillator layers, followed by EM calorimetery with lead glass. A prototype calorimeter system is being built, and will eventually be installed at an ESS test beam line for \textit{in situ} neutron background studies.