Constraining the $R$-symmetric chargino NLSP at the LHC

TL;DR

This paper investigates the phenomenology of Dirac electroweakinos in an $R$-symmetric extension of the MSSM, analyzing LHC constraints on a chargino NLSP scenario with a gravitino LSP, and finds viable parameter regions with low fine-tuning.

Contribution

It provides the first detailed LHC analysis of the chargino NLSP in the $R$-symmetric MRSSM, including prompt and long-lived decay constraints.

Findings

Chargino NLSP can be lighter than the neutralino in the MRSSM.

Viable parameter space exists that satisfies current LHC and Higgs constraints.

Model fine-tuning can be reduced to below 1%.

Abstract

We present a phenomenological study of Dirac electroweakinos in a $U(1)_R$ extension of the MSSM with a strictly $R$-symmetric Higgs sector (MRSSM) and gauge-mediated supersymmetry breaking. One of the distinguishing features of the MRSSM is that the lightest chargino can be lighter than the lightest neutralino. Decays from the NLSP chargino to the gravitino LSP will produce exotic signals. We apply LHC-13 mass limits from both prompt and long-lived searches to the chargino NLSP regime of the MRSSM. Imposing the additional constraints coming from the 125 GeV Higgs and from the electroweak sector, regions of the parameter space are found where the gravitino LSP, chargino NLSP scenario survives all current bounds. We also show that the fine-tuning of the model can reach a level slightly better than sub-percent with our choice of parameters.