Supersymmetry with a Chargino NLSP and Gravitino LSP

TL;DR

This paper explores a unique supersymmetric scenario where the lightest chargino is lighter than the neutralino, leading to distinctive collider signatures involving charginos decaying into W bosons and gravitinos, especially in R-symmetric models.

Contribution

It identifies conditions under which the chargino can be lighter than the neutralino and analyzes the resulting collider signals, highlighting the role of R-symmetry and specific MSSM parameter regions.

Findings

Chargino can be lighter than neutralino in certain models.

Distinctive collider signatures involve chargino decays to W and gravitino.

The scenario is more generic in R-symmetric supersymmetry.

Abstract

We demonstrate that the lightest chargino can be lighter than the lightest neutralino in supersymmetric models with Dirac gaugino masses as well as within a curious parameter region of the MSSM. Given also a light gravitino, such as from low scale supersymmetry breaking, this mass hierarchy leads to an unusual signal where every superpartner cascades down to a chargino that decays into an on-shell W and a gravitino, possibly with a macroscopic chargino track. We clearly identify the region of parameters where this signal can occur. We find it is generic in the context of the R-symmetric supersymmetric standard model, whereas it essentially only occurs in the MSSM when sign(M1) is not equal to sign(M2) = sign(\mu) and tan(beta) is small. We briefly comment on the search strategies for this signal at the LHC.