Probing compressed Higgsinos at the FASER experiment

TL;DR

This paper explores the potential of the FASER experiment to detect long-lived neutral Higgsinos in compressed spectra, which are challenging for main LHC detectors, and finds FASER 2 can probe Higgsino masses up to 130 GeV.

Contribution

It demonstrates the discovery prospects of FASER 2 for long-lived neutral Higgsinos in compressed spectra, filling a gap left by other LHC searches.

Findings

FASER 2 can detect Higgsinos up to 130 GeV mass.

FASER is sensitive to small mass splittings between 4 to 30 MeV.

Complementary to other LHC searches for different Higgsino mass splittings.

Abstract

In the Minimal Supersymmetric Standard Model (MSSM), compressed Higgsinos spectrum ($\Delta m^0 \lesssim 1$ GeV) occurs when $|\mu| \ll |M_1|, |M_2|$ and ${\rm sign}(M_1\cdot M_2)<0$, which leads to a long-lived next-to-lightest neutralino. Such a long-lived neutralino could be copiously produced at the LHC, however escape the detection at the LHC main detectors. We examine the discovery potential at the FASER experiment and find that the FASER 2 could cover the neutral Higgsino mass up to about 130 GeV with mass splitting between 4 to 30 MeV. It is complementary to both the LHC Higgsino search in the $\Delta m^{0,\pm} \gtrsim 1$ GeV region, and displaced vertex and disappearing track searches of charginos with $\Delta m^\pm \lesssim 1$ GeV.