A New Mass Reconstruction Technique for Resonances Decaying to di-tau

TL;DR

This paper introduces a novel mass reconstruction technique for resonances decaying into tau pairs, overcoming limitations of previous methods by using likelihood minimization to accurately determine the original resonance mass.

Contribution

The new method replaces the collinear approximation with a likelihood-based approach, improving mass reconstruction accuracy for tau decays in collider experiments.

Findings

Effective in simulated Z/γ*→ττ and H→ττ events

Validated on real data from the CDF experiment

Expected to enhance Higgs boson searches at LHC and Tevatron

Abstract

Accurate reconstruction of the mass of a resonance decaying to a pair of $\tau$ leptons is challenging because of the presence of multiple neutrinos from $\tau$ decays. The existing methods rely on either a partially reconstructed mass, which has a broad spectrum that reduces sensitivity, or the collinear approximation, which is applicable only to the relatively small fraction of events. We describe a new technique, which provides an accurate mass reconstruction of the original resonance and does not suffer from the limitations of the collinear approximation. The major improvement comes from replacing assumptions of the collinear approximation by a requirement that mutual orientations of the neutrinos and other decay products are consistent with the mass and decay kinematics of a $\tau$ lepton. This is achieved by minimizing a likelihood function defined in the kinematically allowed phase space region. In this paper we describe the technique and illustrate its performance using $Z/\gamma^{*}\to\tau\tau$ and $H\to\tau\tau$ events simulated with the realistic detector resolution. The method is also tested on a clean sample of data $Z/\gamma^{*}\to\tau\tau$ events collected by the CDF experiment at the Tevatron. We expect that this new technique will allow for a major improvement in searches for the Higgs boson at both the LHC and the Tevatron.