Precise Estimate of Charged Wino Decay Rate

Abstract

The Wino is an $\mathrm{SU}(2)_{L}$ triplet Majorana fermion and a well-motivated dark matter candidate. The mass difference between the charged and the neutral Winos is small thanks to the $\mathrm{SU}(2)_{L}$ symmetry. The small mass difference makes the charged Wino meta-stable, which provides disappearing charged track signatures at collider experiments. The constraint on the Wino dark matter at the LHC strongly depends on the Wino lifetime. We compute the next-to-leading order (NLO) correction of the charged Wino decay and make the most precise estimate of the decay rate. We find that the NLO decay rate is determined by the mass difference and scarcely depend on the Wino mass itself in the heavy Wino limit. As a result, we find the NLO correction gives a minor impact on the lifetime of 2-4% increase.