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1. Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor

   https://doi.org/10.1140/epjc/s10052-022-11150-x  

   Augier, C.; Baulieu, G.; Belov, V.; Berge, L.; Billard, J.; Bres, G.; Bret, J-. L.; Broniatowski, A.; Calvo, M.; Cazes, A.; et al (January 2023, The European Physical Journal C)

   Abstract The futureRicochetexperiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 m away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, theRicochetCollaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment’s shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present theRicochetneutron background characterization using$$^3$$ ${}^3$He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to theRicochetGeant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the futureRicochetexperiment and the resulting CENNS detection significance. Our results show that depending on the effectiveness of the muon veto, we expect a total nuclear recoil background rate between 44 ± 3 and 9 ± 2 events/day/kg in the CENNS region of interest, i.e. between 50 eV and 1 keV. We therefore found that theRicochetexperiment should reach a statistical significance of 4.6 to 13.6 $$\sigma $$ $\sigma$for the detection of CENNS after one reactor cycle, when only the limiting neutron background is considered. 

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2. Monitoring the SNS basement neutron background with the MARS detector

   https://doi.org/10.1088/1748-0221/17/03/P03021  

   Akimov, D.; An, P.; Awe, C.; Barbeau, P.S.; Becker, B.; Belov, V.; Bernardi, I.; Blackston, M.A.; Bock, C.; Bolozdynya, A.; et al (March 2022, Journal of Instrumentation)

   Abstract We present the analysis and results of the first datasetcollected with the MARS neutron detectordeployed at the Oak Ridge NationalLaboratory Spallation Neutron Source (SNS) for the purpose ofmonitoring and characterizing the beam-related neutron (BRN) backgroundfor the COHERENT collaboration. MARS was positionednext to the COH-CsI coherent elastic neutrino-nucleus scattering detectorin the SNS basement corridor. This is the basement location ofclosest proximity to the SNS target and thus, of highest neutrino flux,but it is also well shielded from the BRN flux by infill concreteand gravel. These data show the detector registered roughly one BRN per day.Using MARS' measured detection efficiency, the incomingBRN flux is estimated to be 1.20 ± 0.56 neutrons/m^2/MWhfor neutron energies above ∼3.5 MeV and up to a few tens of MeV.We compare our results with previous BRN measurements in the SNS basement corridorreported by other neutron detectors. 

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3. Neutron tagging can greatly reduce spallation backgrounds in Super-Kamiokande

   https://doi.org/10.1103/PhysRevD.111.023014  

   Nairat, Obada; Beacom, John F; Li, Shirley Weishi (January 2025, Physical Review D)

   Super-Kamiokande’s spallation backgrounds—the delayed beta decays of nuclides following cosmic-ray muons—are nearly all produced by the small fraction of muons with hadronic showers. We show that these hadronic showers also produce neutrons; their captures can be detected with high efficiency due to the recent addition of dissolved gadolinium to Super-Kamiokande. We show that new cuts based on the neutron tagging of showers could reduce spallation backgrounds by a factor of at least four beyond present cuts. With further work, this could lead to a near elimination of detector backgrounds above about 6 MeV, which would significantly improve the sensitivity of Super-Kamiokande. These findings heighten the importance of adding gadolinium to Hyper-Kamiokande, which is at a shallower depth. Further, a similar approach could be used in other detectors, for example, the JUNO liquid-scintillator detector, which is also at a shallower depth. Published by the American Physical Society2025 

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4. Demonstration of neutron identification in neutrino interactions in the MicroBooNE liquid argon time projection chamber

   https://doi.org/10.1140/epjc/s10052-024-13423-z  

   Abratenko, P; Alterkait, O; Aldana, D Andrade; Arellano, L; Asaadi, J; Ashkenazi, A; Balasubramanian, S; Baller, B; Barnard, A; Barr, G; et al (October 2024, The European Physical Journal C)

   Abstract A significant challenge in measurements of neutrino oscillations is reconstructing the incoming neutrino energies. While modern fully-active tracking calorimeters such as liquid argon time projection chambers in principle allow the measurement of all final state particles above some detection threshold, undetected neutrons remain a considerable source of missing energy with little to no data constraining their production rates and kinematics. We present the first demonstration of tagging neutrino-induced neutrons in liquid argon time projection chambers using secondary protons emitted from neutron-argon interactions in the MicroBooNE detector. We describe the method developed to identify neutrino-induced neutrons and demonstrate its performance using neutrons produced in muon-neutrino charged current interactions. The method is validated using a small subset of MicroBooNE’s total dataset. The selection yields a sample with$$60\%$$ $60\%$of selected tracks corresponding to neutron-induced secondary protons. At this purity, the integrated efficiency is 8.4% for neutrons that produce a detectable proton. 

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5. Evaluation of gadolinium’s action on water Cherenkov detector systems with EGADS

   https://doi.org/10.1016/j.nima.2020.163549  

   Marti, LI; et, al (January 2020, Nuclear instruments methods n physics research)

   Used for both proton decay searches and neutrino physics, large water Cherenkov (WC) detectors have been very successful tools in particle physics. They are notable for their large masses and charged particle detection capabilities. While current WC detectors reconstruct charged particle tracks over a wide energy range, they cannot efficiently detect neutrons. Gadolinium (Gd) has the largest thermal neutron capture cross section of all stable nuclei and produces an 8 MeV gamma cascade that can be detected with high efficiency. Because of the many new physics opportunities that neutron tagging with a Gd salt dissolved in water would open up, a large-scale R&D; program called EGADS was established to demonstrate this technique’s feasibility. EGADS features all the components of a WC detector, chiefly a 200-ton stainless steel water tank furnished with 240 photo-detectors, DAQ, and a water system that removes all impurities from water while keeping Gd in solution. In this paper we discuss the milestones towards demonstrating the feasibility of this novel technique, and the features of EGADS in detail. 

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