Probing the 3+1 neutrino model in the SHiP experiment

TL;DR

This paper evaluates the SHiP experiment's ability to detect or constrain the 3+1 neutrino model using a dual-baseline setup and advanced statistical methods, improving sensitivity to sterile neutrino parameters.

Contribution

It extends previous work by applying a dual-baseline approach and refined statistical analysis to enhance sensitivity to sterile neutrino mixing parameters in the 3+1 model.

Findings

NSND-only configuration probes |U_{α4}|^2 ≥ 0.1 near Δm_{41}^2 ≈ 10^3 eV^2

Including FSND improves sensitivity by a factor of 2 to 10

Dual-baseline approach removes sensitivity curve kinks caused by flavor cancellation

Abstract

In this study, as an extension of our previous work, we estimate the sensitivity of the Search for Hidden Particles (SHiP) experiment to the 3+1 model using the charged-current deep inelastic scattering event spectrum. We employ the Feldman-Cousins method with a parametric bootstrap to account for nuisance parameters and systematic uncertainties. In the previous study, we proposed a dual baseline approach by suggesting Far SND (FSND) at 120 m with Near SND (NSND) at 27 m. We employ the same approach in this study. The NSND-only configuration can probe mixing parameters of $|U_{\alpha4}|^2 \gtrsim 0.1$ near $\Delta m_{41}^2 \sim 10^3\,\mathrm{eV}^2$, with a reduction of normalized systematic uncertainties from 20\% to 10\% improving sensitivity by roughly a factor of two. Moreover, the inclusion of FSND significantly enhances the sensitivity by a factor of 2 to 10 depending on the flavor and the systematic uncertainty. In two-flavor mixing scenarios, a cancellation between neutrino appearance and disappearance generates kinks in the sensitivity curves, that are vanished in the dual-baseline approach.