Heavy Neutrinos and the Kinematics of Tau Decays

TL;DR

This paper introduces a model-independent method to constrain the coupling of tau leptons to heavy neutrinos using only decay kinematics, enabling more robust limits without relying on specific decay models.

Contribution

A novel approach that derives limits on heavy neutrino coupling from tau decay kinematics alone, applicable to large datasets from B factories.

Findings

Potential to set limits on |U_tau4|^2 as low as 10^-7 to 10^-3

Applicable to heavy neutrino masses between 100 MeV and 1.2 GeV

Requires minimal assumptions about heavy neutrino decay modes

Abstract

Searches for heavy neutrinos often rely on the possibility that the heavy neutrinos will decay to detectable particles. Interpreting the results of such searches requires a particular model for the heavy-neutrino decay. We present a method for placing limits on the probability that a tau can couple to a heavy neutrino, |U_tau4|^2, using only the kinematics of semi-leptonic tau decays, instead of a specific model. Our study suggests that B factories with large datasets, such a Belle and BaBar, may be able to place stringent limits on |U_tau4|^2 as low as O(10^-7 - 10^-3) when 100 MeV < m_4 < 1.2 GeV, utilizing minimal assumptions regarding the decay modes of heavy neutrinos.