# Response of CsI[Na] to Nuclear Recoils: Impact on Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS)

## TL;DR

This paper presents a refined measurement of the quenching factor in CsI[Na], improving the accuracy of CE$
u$NS detection and enhancing the agreement with Standard Model predictions, which is crucial for new physics searches.

## Contribution

The study provides a new, more precise quenching factor measurement for CsI[Na], correcting systematic effects and reducing uncertainty, thereby improving CE$
u$NS experimental analysis.

## Key findings

- Reduced uncertainty in quenching factor by a factor of four.
- Enhanced agreement between experimental data and Standard Model predictions.
- Highlighting the importance of accurate quenching factors in new physics searches.

## Abstract

A new measurement of the quenching factor for low-energy nuclear recoils in CsI[Na] is presented. Past measurements are revisited, identifying and correcting several systematic effects. The resulting global data are well-described by a physics-based model for the generation of scintillation by ions in this material, in agreement with phenomenological considerations. The uncertainty in the new model is reduced by a factor of four with respect to an energy-independent quenching factor initially adopted as a compromise by the COHERENT collaboration. A significantly improved agreement with Standard Model predictions for the first measurement of CE$\nu$NS is generated. We emphasize the critical impact of the quenching factor on the search for new physics via CE$\nu$NS experiments.