Mass Splitting between Charged and Neutral Winos at Two-Loop Level

TL;DR

This paper provides a precise two-loop calculation of the mass splitting between charged and neutral winos, crucial for interpreting LHC searches for long-lived charged winos in supersymmetric models.

Contribution

It presents the first full two-loop level calculation of wino mass splitting, refining previous estimates and impacting experimental constraints.

Findings

Mass splitting is reduced by a few MeV at two-loop level.

Charged wino lifetime increases by about 30%.

Current experimental bounds on wino mass are improved by approximately 10%.

Abstract

The recent result of the higgs search at the LHC experiment has lead to more attention to the supersymmetric standard models with heavy sfermions. Among them, the models with the almost pure wino being the lightest supersymmetric particle (LSP) have been widely discussed due to their success in providing a consistent dark matter candidate. The notable phenomenological feature of the wino LSP is the degeneracy with its charged SU(2)_L partner (the charged wino) in mass. The tiny mass splitting makes the charged wino long-lived, which allows us to detect the wino production at the LHC experiment by searching for the disappearing charged tracks inside the detectors. Since the reach of the experiment is sensitive to the mass splitting, it is mandatory to estimate it very precisely. We therefore perform a full calculation of the mass splitting at two-loop level, and find that the splitting is reduced by a few MeV compared to the one-loop calculation. This reduction leads to about a 30 % longer lifetime of the charged wino, with which the current constraint on the wino mass by the ATLAS experiment is improved by about 10 %.