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

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 monophotons 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 $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ should be sensitive to light higgsinos at the $5\ensuremath{\sigma}$ level for $\ensuremath{\mu}<170\text{ }\text{ }\mathrm{GeV}$ with a $S/B\ensuremath{\sim}8.5%$. For an integrated luminosity of $1000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ (which should be possible at a high-luminosity LHC) the corresponding sensitivity to $\ensuremath{\mu}$ 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 flavor vs opposite flavor dileptons is $\ensuremath{\sim}10--15\text{ }\text{ }\mathrm{GeV}$ smaller, but does not suffer the systematic uncertainty from the normalization of the background.