Abstract
The HIBEAM/NNBAR program is a proposed two-stage experiment at the European Spallation Source focusing on searches for baryon number violation via processes in which neutrons convert to antineutrons. This paper outlines the computing and detector simulation framework for the HIBEAM/NNBAR program. The simulation is based on predictions of neutron flux and neutronics together with signal and background generation. A range of diverse simulation packages are incorporated, including Monte Carlo transport codes, neutron ray-tracing simulation packages, and detector simulation software. The common simulation package in which these elements are interfaced together is discussed. Data management plans and triggers are also described.
Highlights
The HIBEAM/NNBAR program [1] for the European Spallation Source (ESS) is a future sequence of experiments to search for beyond Standard Model (BSM) physics appearing as baryon number violation (BNV)
The characteristic semi-spherical topology generated from an n A annihilation following extranuclear n → ncan retain up to ∼ 1.88 GeV of total invariant mass and a rather low total momentum across an average of 4-5 pions expected to be emitted from an event [8, 9]
The simulation needs for the HIBEAM/NNBAR program are mostly driven by the reconstruction of the annihilation event in a detector, as well as computing of topological, kinematic, and timing characteristics of any backgrounds for their comparative rejection; neutron optics, as well as magnetic and radiation shielding along the beamline, are major contributors to the overall computational scheme
Summary
The HIBEAM/NNBAR program [1] for the European Spallation Source (ESS) is a future sequence of experiments to search for beyond Standard Model (BSM) physics appearing as baryon number violation (BNV). As a search for a rare BNV process, any definitive discovery would require the observation of at least one free neutron oscillating into an antineutron above what are expected to be, following appropriate trigger and analysis selections, tiny backgrounds, as was achieved at the last such experiment [5]. As the HIBEAM/NNBAR program is searching for a rare process, the average data taking trigger rate is mainly driven by natural and neutron beam-generated backgrounds. Given the high neutron fluxes reaching the target of the experiments, one still expects around 105 and 107 photons/s from neutron capture for HIBEAM and NNBAR, respectively Such rates are quite manageable for a modern trigger system, but it can provide high counting rates within sub-detector elements, and can be a potential source of background to the signal in random coincidence with fast neutrons released during the spallation process, along with cosmic rays. All of these components are key simulation and computation drivers within the HIBEAM/NNBAR program
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