Neutron capture-induced nuclear recoils as background for CE$\nu$NS~measurements at reactors

Abstract

Nuclear reactors represent a promising neutrino source for CE$\nu$NS (coherent-elastic neutrino-nucleus scattering) searches. However, reactor sites also come with high ambient neutron flux. Neutron capture-induced nuclear recoils can create a spectrum that strongly overlaps the CE$\nu$NS signal for recoils $\lesssim$\,100\,eV for nuclear reactor measurements in silicon or germanium detectors. This background can be particularly critical for low-power research reactors providing a moderate neutrino flux. In this work we quantify the impact of this background and show that, for a measurement 10\,m from a 1\,MW reactor, the effective thermal neutron flux should be kept below $\sim$~7$\times$~10${}^{-4}$\,n/cm${}^2$s so that the CE$\nu$NS events can be measured at least at a 5$\sigma$ level with germanium detectors in 100~kg\,yr exposure time. This flux corresponds to 60\% of the sea-level flux but needs to be achieved in a nominally high-flux (reactor) environment. Improved detector resolution can help the measurements, but the thermal flux is the key parameter for the sensitivity of the experiment. For silicon detectors, the constraint is even stronger and thermal neutron fluxes must be near an order of magnitude lower. This constraint highlights the need of an effective thermal neutron mitigation strategy for future low threshold CE$\nu$NS searches. In particular, the neutron capture-induced background can be efficiently reduced by active veto systems tagging the deexcitation gamma following the capture.

arXiv comment7 pages, 3 figures, 1 table

References in corpus (38)

• Improved Predictions of Reactor Antineutrino Spectra
• Observation of Coherent Elastic Neutrino-Nucleus Scattering
• First results from the CRESST-III low-mass dark matter program
• SENSEI: Direct-Detection Results on sub-GeV Dark Matter from a New Skipper-CCD
• Exclusive Vector Meson Production in Relativistic Heavy Ion Collisions
• First Dark Matter Constraints from a SuperCDMS Single-Charge Sensitive Detector
• Single-electron and single-photon sensitivity with a silicon Skipper CCD
• Searching for low-mass dark matter particles with a massive Ge bolometer operated above-ground
• First germanium-based constraints on sub-MeV Dark Matter with the EDELWEISS experiment
• Constraints on low-mass, relic dark matter candidates from a surface-operated SuperCDMS single-charge sensitive detector
• First results from the NEWS-G direct dark matter search experiment at the LSM
• Reactor Neutrino Spectra
• Light Dark Matter Search with a High-Resolution Athermal Phonon Detector Operated Above Ground
• Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes
• Coherent Neutrino Scattering with Low Temperature Bolometers at Chooz Reactor Complex
• Improved Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay
• Constraints on elastic neutrino nucleus scattering in the fully coherent regime from the CONUS experiment
• Measurement of Coherent Elastic Neutrino-Nucleus Scattering from reactor antineutrinos
• Exploring low-energy neutrino physics with the Coherent Neutrino Nucleus Interaction Experiment (CONNIE)
• Results on Low-Mass Weakly Interacting Massive Particles from an 11 kg-day Target Exposure of DAMIC at SNOLAB
• Exploring CEvNS with NUCLEUS at the Chooz Nuclear Power Plant
• EXCESS workshop: Descriptions of rising low-energy spectra
• Gram-scale cryogenic calorimeters for rare-event searches
• Coherent Elastic Neutrino-Nucleus Scattering at the European Spallation Source
• Sterile Neutrinos, Coherent Scattering and Oscillometry Measurements with Low-temperature Bolometers
• Thermal detection of single e-h pairs in a biased silicon crystal detector
• Charge Coupled Devices for detection of coherent neutrino-nucleus scattering
• Search for coherent elastic neutrino-nucleus scattering at a nuclear reactor with CONNIE 2019 data
• First results from a search for coherent elastic neutrino-nucleus scattering (CE$\nu$NS) at a reactor site
• First results of the nuGeN experiment on coherent elastic neutrino-nucleus scattering
• First upper limits on neutrino electromagnetic properties from the CONUS experiment
• First ground-level laboratory test of the two-phase xenon emission detector RED-100
• Pulse-shape discrimination between electron and nuclear recoils in a NaI(Tl) crystal
• First observation of isolated nuclear recoils following neutron capture for dark matter calibration
• Constraints on Bosonic Dark Matter with Low Threshold Germanium Detector at Kuo-Sheng Reactor Neutrino Laboratory
• Unfolding Neutron Spectrum with Markov Chain Monte Carlo at MIT Research Reactor with He-3 Neutral Current Detectors
• $\text{nrCascadeSim}$ -- A simulation tool for nuclear recoil cascades resulting from neutron capture
• Discrimination of nuclear and electronic recoil events using plasma effect in germanium detectors