Same Sign versus Opposite Sign Dileptons as a Probe of Low Scale Seesaw Mechanisms

TL;DR

This paper investigates how the ratio of same sign to opposite sign dileptons at colliders can reveal details about low-scale seesaw mechanisms and distinguish between different models like type I and inverse seesaw.

Contribution

It introduces a method to use dilepton charge ratios to probe the nature of low-scale seesaw models and demonstrates how collider measurements can differentiate seesaw types.

Findings

The ratio $R_{\ell\ell}$ varies between 0 and 1 depending on the neutrino mass matrix.

Measurement of $R_{\ell\ell}$ can distinguish between seesaw models at colliders.

Degeneracy of right-handed neutrinos is crucial for observing the effect.

Abstract

We calculate the ratio $R_{\ell\ell}$ of same sign (SS) to opposite sign (OS) dileptons in type I and generalized inverse seesaw models and show that it can be anywhere between 0 and 1 depending on the detailed texture of the right-handed neutrino mass matrix. Measurement of $R_{\ell\ell}$ in hadron colliders can therefore provide a way to probe the nature of seesaw mechanism and also to distinguish between the two types of seesaw mechanisms. We work within the framework of left-right symmetric model as an example. We emphasize that coherence of the final states in the $W_R$ decay is crucial for this discussion and it requires the right-handed neutrinos to be highly degenerate. We isolate the range of parameters in the model where this effect is observable at the LHC and future colliders.