Monojet plus soft dilepton signal from light higgsino pair production at LHC14

TL;DR

This paper explores the detection prospects of light higgsinos at the LHC14 by analyzing monojet events with soft dileptons, proposing a method to improve signal sensitivity amidst challenging backgrounds.

Contribution

It introduces a novel approach of requiring soft dileptons in monojet events to enhance higgsino detection sensitivity at the LHC, addressing previous background suppression challenges.

Findings

LHC14 can detect higgsinos with  < 170 GeV at 5c with 300 fb^{-1}.

Sensitivity extends to over 200 GeV with 1000 fb^{-1} at high luminosity.

Rate asymmetry measurements offer a systematic uncertainty-resistant detection method.

Abstract

Naturalness arguments imply the existence of higgsinos lighter than 200-300 GeV. However, because these higgsinos are nearly mass degenerate, they release very little visible energy in their decays, and (even putting aside triggering issues) signals from electroweak higgsino pair production typically remain buried under Standard Model backgrounds. Prospects for detecting higgsino pair production via events with monojets or mono-photons from initial state radiation are also bleak because of signal-to-background rates typically at the 1% level. Here, we consider the possibility of reducing backgrounds by requiring the presence of soft daughter leptons from higgsino decays in monojet events. We find that LHC14 experiments with an integrated luminosity of 300 fb^{-1} should be sensitive to light higgsinos at the 5\sigma level for \mu < 170 GeV with a S/B ~ 8.5%. For an integrated luminosity of 1000 fb^{-1} (which should be possible at a high luminosity LHC) the corresponding sensitivity to \mu extends to over 200 GeV though the systematic uncertainty would have to be controlled to considerably better than 5%. The corresponding reach from measurements of the rate asymmetry between monojet events with same flavour vs. opposite flavour dileptons is ~10-15 GeV smaller, but does not suffer the systematic uncertainty from the normalization of the background.