Title: HIBEAM-NNBAR Cluster
DNr: NAISS 2023/22-154
Project Type: NAISS Small Compute
Principal Investigator: Bernhard Meirose <bernhard.meirose@hep.lu.se>
Affiliation: Lunds universitet
Duration: 2023-03-01 – 2024-03-01
Classification: 10301
Homepage: https://nnbar.eu/


HIBEAM-NNBAR is a proposed two-stage program of experiments at the European Spallation Source (ESS) designed to search for neutrons converting into antineutrons and/or sterile neutrons. Such an observation would indicate baryon number violation, a fundamental condition for baryogenesis, the physical process that is hypothesized to have taken place during the early universe to produce baryonic asymmetry, i.e. the imbalance of matter (baryons) and antimatter (antibaryons) in the observed universe. In addition to shedding light on the baryon asymmetry of the universe, neutron conversions would provide the first falsification outside of the neutrino sector of the Standard Model (SM) of particle physics. Taking advantage of the unique potential of the ESS, the high precision searches for neutron conversions to be performed by the HIBEAM-NNBAR collaboration will culminate in an ultimate sensitivity increase of three orders of magnitude beyond the previously attained limit obtained at the Institut Laue Langevin (ILL) in the early 1990s. The Lund HIBEAM-NNBAR group is involved in many aspects of the experiment, including but not limited to the design of the annihilation detector and of the software framework, which are currently under intense development by the collaboration. The annihilation detector is the main necessary instrumentation of the experiments, which is used to reconstruct the final state (~5 pions with momenta 100-300 MeV) arising from an antineutron annihilating with a nucleon in the carbon target. The computing resources being applied for, will be used to run several detector simulations (different geometries, materials, etc) in Geant4. Backgrounds to the experiment will be generated both in Geant4 and with the general purpose Monte Carlo particle transport simulation code PHITS (Particle and Heavy Ion Transport code System).