Status of the Design of an Annihilation Detector to Observe Neutron-Antineutron Conversions at the European Spallation Source

Abstract

The goal of the HIBEAM/NNBAR program is to search for baryon number violation via the conversion or oscillation of neutrons into sterile neutrons and/or antineutrons at the European Spallation Source. A key experimental component of the program is the construction of an annihilation detector to directly observe the production of an antineutron following the oscillation. Design studies for the annihilation detector are presented. The predicted response of the detector models are studied using Geant4 simulations made with Monte Carlo simulations of the annihilation signal topology and cosmic ray backgrounds. Particle identification and sensitive discriminating observables, such as invariant mass and sphericity, are shown.

Feebly-interacting particles: FIPs 2020 workshop report

“…Different detector choices are under consideration. These include the development of a detector concept based on a TPC, hadronic range detector and lead-glass-based electromagnetic calorimeter [1653], as well as a modified version of the WASA detector [1658]. The propagation region for neutrons in each of the above configurations is magnetically controlled, such that the magnetic field would match that in any dark sector, thereby ensuring degeneracy and avoiding suppression of the neutron-antineutron transition while allowing the feeble mixing to take place.…”

“…Presently under construction, the European Spallation Source (ESS) [1651] will be the world's brightest neutron source and will open a new discovery window for BNV searches. The HIBEAM/NNBAR project [1652,1653,1654,1655] is a proposed multi-stage program for the ESS to take advantage of this that can achieve an ultimate search sensitivity improvement of three orders of magnitude compared to that available at other facilities. The program's first stage is termed High Intensity Baryon Extraction and Measurement (HIBEAM).…”

The Development of the NNBAR Experiment

“…An overview of the design work is given in this Section, which is based on the detector model described in Ref. [43].…”

“…The current baseline detector concept [43] comprises silicon tracking, placed within a 2cm thick aluminium beampipe. The TPC surrounds the beampipe.…”

“…Such quantities include the invariant mass (𝑊) and sphericity (𝑆) of the observed particle system in the detector. Their computation uses algorithms to identify and reconstruct particles (neutral and charged pions and protons) [43]. An example of another sensitive variable is the difference in timing between the first and last scintillator hits (𝛥𝑇).…”