High-multiplicity neutron events registered by NEMESIS experiment

Discussion timeslot (ZOOM-Meeting): 16. July 2021 - 18:00
ZOOM-Meeting URL: https://icrc2021.desy.de/pf_access_abstracts
Corresponding Session: https://icrc2021-venue.desy.de/channel/Presenter-Forum-1-Evening-All-Categories/48
Abstract:
'Neutron-induced interactions contribute to the signal-mimicking background in deep-underground searches for exotic phenomena such as Dark Matter, neutrino-less double beta decay, proton decay, etc. Apart from radioactive decay, the primary source of neutrons underground are high-energy muons from cosmic showers. While the maximum number of fission neutrons is around six and energies around one MeV, muon-induced interactions may generate hundreds of neutrons, also with high energies. Furthermore, these processes are not yet reproduced numerically with sufficient reliability. The main goal of the NEMESIS experiment is to improve our knowledge and understanding of cosmic muon-induced neutron production in high-Z targets. NEMESIS (New Emma MEasurement with neutronS In cosmic Showers) is taking data at a depth of 210 m.w.e. in Callio Lab at the Pyhäsalmi mine in Finland. The neutron setup consists of 14 $^{3}He$ counters in polyethylene blocks. Data from the helium counters and muon scintillation arrays are collected by proprietary electronics digitizing signal waveforms with adequate time overlap to detect delayed coincidences. The presented neutron spectra will include a 300-day run with a 565 kg Pb target, a 150-day run without the target, and the outcome of the relevant Geant4 simulations. The extracted neutron multiplicity spectrum shows a linear behaviour on a doubly logarithmic scale. The largest registered event had 36 neutrons. Correcting for a 10% detection efficiency, determined with Geant4, indicates the emission of 360 neutrons in this mega-event.'

Authors: Marcin Kasztelan | Timo Enqvist | Jacek Szabelski | Wladyslaw Henryk Trzaska | Karol Jędrzejczak | Pasi Kuusiniemi | Julia Puputti | Marika Przybylak | Jari Joutsenvaara | Jerzy Orzechowski
Collaboration: NEMESIS

Indico-ID: 597
Proceeding URL: https://pos.sissa.it/395/497