Reconstruction of interaction vertices for background rejection for the COH-CryoCsI-1

Coherent elastic neutrino-nucleus scattering (CEvNS) is a neutral-current interaction predicted by the standard model whose sole observable is a low-energy nuclear recoil. The first detection of CEvNS was achieved by the COHERENT collaboration using a cesium iodide (CsI) detector in 2017, at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Such a discovery took nearly 40 years after its prediction given the experimental challenges, among them, the presence of background noise, the keV-scale recoil energies of the elastically scattered nuclei. Further data analysis revealed the detection of CEvNS on argon in 2021, followed by a subsequent observation on germanium in 2023. In addition to being another test of the the standard model, CEvNS can be used as a probe for the discovery of new physics.

Another detector using a 10 kg undoped CsI crystal has been planned (COH-CryoCsI-1) to continue the search for accelerator-produced dark matter at the SNS, a task that remains unresolved, using SiPM's and operating at a temperature near 40 K to increase the light yield. I present the progress and challenges of developing a reconstruction technique that could lead to the distinction between neutron backgrounds and nuclear recoils produced by the CEvNS interactions. All the findings have been developed so far by analyzing simulations of scintillations inside a CsI crystal in a GEANT4-based application called Gears.