Speaker
Description
The European Spallation Source (ESS) under construction in Lund, Sweden, is set to become the brightest cold spallation neutron source in the world. Neutrons are produced by a 2 GeV proton beam hitting a tungsten target and moderated in cold and thermal moderators.
The HIBEAM/NNBAR program is a proposed two-stage experiment at the ESS to search for baryon number violation [1]. The primary goal of the program is to produce new insights into the origins of baryogenesis by performing searches for neutron–antineutron oscillations and conversions of a neutron into a sterile neutron. The first stage of the program, HIBEAM (High-Intensity Baryon Extraction and Measurement) represents the first search for neutron to antineutron oscillations at a spallation source [2] and will be able to provide the most stringent limit of the free neutron-antineutron oscillation time to date.
In this talk, an overview over the planned beamline and detection systems will be given and the current status of development will be discussed. The neutron optics system as well as the radiation shielding have been designed and optimized using Monte Carlo simulations. The beamline is also being designed so that the magnetic field inside it can be controlled, as the processes intended to be studied are highly sensitive to external fields.
The HIBEAM annihilation detector must be able to identify the multi-pion state created by the annihilation of an antineutron in a carbon target. The planned design consists of a TPC surrounded by the WASA electromagnetic calorimeter [3] as well as scintillation detectors used to veto cosmic background. The performance of this detector has been evaluated in simulations and detector prototypes have been constructed. A first in-beam test of these prototypes was performed at the Cyclotron Centre Bronowice in Krakow, Poland. Elastic scattering of 190 MeV protons from a CD2 target was measured. First results from this experiment will be presented.
[1] Addazi et al. “New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the HIBEAM/NNBAR experiment at the European Spallation Source”, J.Phys.G: Nucl. Part. Phys. 48 (2021) 7, 070501
[2] Santoro et al. “The HIBEAM Instrument at the European Spallation Source”, J. Phys. G: Nucl. Part. Phys. 52 (2025) 040501
[3] Bargholtz et al. “The WASA Detector Facility at CELSIUS“ , Nucl.Instrum.Meth. A594 (2008) 339-350