Development of an innovative neutron detector for the European Spallation Source (ESS)

ESS will be the world´s most powerful facility for research using neutrons.

The HIBEAM (High Intensity Baryon Extraction and Measurement) collaboration  proposed a program for neutron conversion searches at ESS to look for baryon number violation and address open questions in physics, such as the origin of the matter-antimatter asymmetry and the nature of the missing mass of the universe, the dark matter.

The HIBEAM project will investigate the existence of sterile neutrons, which are part of a "dark" sector of particles.

These particles can be observed through mixing, which involves the conversion of long-lived, electrically neutral particles with their counterparts in the dark sector, and vice versa.

One of the primary processes with the highest probability for detecting dark neutrons is the search for the transformation of neutrons (n) into their dark counterparts (n´).

Observing the effects of neutron to dark neutron oscillation involves conducting experiments that look for anomalous neutron disappearance that manifests as a reduction in neutron counts, as neutrons that have converted into dark neutrons become undetectable by neutron detectors.

The experimental challenge lies in detecting the loss of neutrons within the intense neutron beams generated by the ESS.

To observe this transition, specialized neutron detectors are required to detect the reduction in neutron counts, indicating the potential conversion of neutrons into dark neutrons.

The requirement for the neutron detector is particularly demanding as it necessitates the capability to detect a minute reduction in the counting rate of incident neutrons, on the order of 10^-6 to 10^-7. This poses a significant challenge, primarily due to the need for highly precise characterization of the neutron beam.

Currently, there is no existing detector with the necessary features to meet these stringent criteria. The primary objective is to conceptualize a detector fulfilling the experiment´s requirements.