Search for New Physics in SHiP and at future colliders

TL;DR

This paper evaluates SHiP's potential to detect hidden particles like sterile neutrinos and dark photons, showing it can significantly improve current sensitivity and complement future collider searches.

Contribution

It provides a comprehensive analysis of SHiP's reach in probing the $ u$MSM and $U(1)$ dark photon models, highlighting its potential to explore new physics parameter spaces.

Findings

SHiP can improve sensitivity to Heavy Neutral Leptons below 2 GeV by several orders of magnitude.

SHiP can explore a large part of the $ u$MSM parameter space below the B meson mass.

SHiP can significantly constrain $U(1)$ dark photons.

Abstract

SHiP is a newly proposed fixed-target experiment at the CERN SPS with the aim of searching for hidden particles that interact very weakly with SM particles. The work presented in this document investigates SHiP's physics reach in the parameter space of the Neutrino Minimal Standard Model ($\nu$MSM), which is a theory that could solve most problems left open by the Standard Model with sterile neutrinos. A model introducing an extra $U(1)$ symmetry in the hidden sector, providing a natural candidate for dark matter, is also explored. This work shows that the SHiP experiment can improve by several orders of magnitude the sensitivity to Heavy Neutral Leptons below 2 GeV, scanning a large part of the parameter space below the $B$ meson mass. The remainder of the $\nu$MSM parameter space, dominated by right-handed neutrinos with masses above 2 GeV, can be explored at a future $e^+e^-$ collider. Similarly, SHiP can greatly improve present constraints on $U(1)$ dark photons.