Loop effect in the coherent neutrino-nucleus scattering

TL;DR

This paper explores how neutrino interactions with nuclei can be affected by exotic fermions and loop effects, revealing new recoil spectra and constraining model parameters using experimental data.

Contribution

It introduces a comprehensive analysis of loop-level contributions in neutrino-nucleus scattering within a simplified model, extending previous tree-level studies.

Findings

Loop effects significantly alter the recoil spectrum.

Constraints on couplings are derived from COHERENT data.

Parameter space with heavy fermions is constrained by loop contributions.

Abstract

A connection between the neutrino and an exotic fermion is described in the general neutrino model. In this model the neutrinos can convert into the new fermion and thus the interaction leads to novel recoil spectrum in the neutrino scattering experiments. We study the general neutrino interaction by evaluating both the tree-level and loop-level contributions to the coherent elastic neutrino-nucleus scattering. We illustrate the scattering by taking the framework of a simplified neutrino model with a Dirac fermion $\chi$ and a spin-0 mediator. For the CP phase in the quark sector being 0 and $\pi/2$, the detection processes are dominated by the tree-level and loop-level contribution, respectively. We investigate the constraints on the couplings between the mediator and the new particle $\chi$ or the quarks by fitting to the COHERENT data. The parameter space with $m_\chi$ larger than the maximal energy of incoming neutrinos can be also constrained by including the loop-level contribution.