CE$\hat{I}½$NS Search with Cryogenic Sapphire Detectors at MINER: Results from the TRIGA reactor data and Future Sensitivity at HFIR

Abstract

We report on a search for coherent elastic neutrino--nucleus scattering (CE$\hat{I}½$NS) using cryogenic sapphire (Al${}_2$O${}_3$) detectors deployed at the Mitchell Institute Neutrino Experiment at Reactor (MINER), located near the 1~MW${}_{\text{th}}$ TRIGA research reactor at Texas A\&M University. The experiment operated with a primary detector mass of 72~g and achieved a baseline energy resolution of $\sim 40$~eV. Using exposures of 158~g-days (reactor-on) and 381~g-days (reactor-off), we performed a statistical background subtraction in the energy region of 0.25--3~keV. A GEANT4 simulation has been performed to understand the reactor-correlated background present in the data and it agrees with our observations. The resulting best-fit ratio of the observed CE$\hat{I}½$NS rate to the Standard Model prediction after rejecting the reactor induced background from the data with the help of simulation, is $\ddot{I}=0.26\pm 1534.74(\mathrm{stat})\pm 0.05(\mathrm{sys})$ with a significance of $0.007\pm 0.022(\mathrm{stat})\pm 0.001(\mathrm{sys})$. This low significance indicates a high background rate at low energies. To have enhanced sensitivity, the MINER collaboration plans to relocate the experiment to the 85~MW${}_{\text{th}}$ High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). With improved shielding, increased detector mass, and higher antineutrino flux, the upgraded setup is projected to achieve a 3$\ddot{I}ƒ$ CE$\hat{I}½$NS detection within 30~kg$\cdot$days of exposure.

12 pages and 12 figures