A mass reconstruction technique for a heavy resonance decaying to $\tau^+\tau^-$

TL;DR

This paper introduces a novel mass reconstruction method for heavy resonances decaying to tau pairs, utilizing the perpendicular momentum component and decay product masses, enabling accurate mass determination without efficiency loss.

Contribution

The method reconstructs resonance mass by sampling kinematic variables based on their probability distributions, independent of the tau's origin, demonstrated through MC simulations at 13 TeV.

Findings

Achieves 20-40% mass resolution ratio.

No efficiency loss in mass reconstruction.

Validated with MC simulations of pp collisions.

Abstract

For a resonance decaying to $\tau^+\tau^-$, it is difficult to reconstruct its mass accurately because of the presence of neutrinos in the decay products of the $\tau$ leptons. If the resonance is heavy enough, we show that its mass can be well determined by the momentum component of the $\tau$ decay products perpendicular to the velocity of the $\tau$ lepton, $p_{\perp}$, and the mass of the visible/invisible decay products, $m_{vis/inv}$, for $\tau$ decaying to hadrons/leptons. By sampling all kinematically allowed values of $p_{\perp}$ and $m_{vis/inv}$ according to their joint probability distributions determined by the MC simulations, the mass of the mother resonance is assumed to lie at the position with the maximal probability. Since $p_{\perp}$ and $m_{vis/inv}$ are invariant under the boost in the $\tau$ lepton direction, the joint probability distributions are independent upon $\tau$'s origin. Thus this technique is able to determine the mass of an unknown resonance with no efficiency loss. It is tested using the MC simulations of the physics processes $ pp \to Z/h(125)/h(750)+X\to \tau\tau+X$ at 13~TeV. The ratio of the full width at half maximum and the peak value of the reconstructed mass distribution is found to be 20\%-40\% using the information of missing transverse energy.