Precision Measurement of the Mass of the $\tau$ Lepton

TL;DR

This paper reports a highly precise measurement of the tau lepton mass using an energy scan near the tau pair production threshold with the BESIII detector, analyzing various decay channels.

Contribution

The study provides the most precise single-measurement value of the tau lepton mass using a dedicated energy scan and maximum likelihood analysis.

Findings

Tau lepton mass measured as 1776.91 MeV/c^2

Achieved the most precise single-measurement value

Used multiple decay channels for analysis

Abstract

An energy scan near the $\tau$ pair production threshold has been performed using the BESIII detector. About $24$ pb$^{-1}$ of data, distributed over four scan points, was collected. This analysis is based on $\tau$ pair decays to $ee$, $e\mu$, $eh$, $\mu\mu$, $\mu h$, $hh$, $e\rho$, $\mu\rho$ and $\pi\rho$ final states, where $h$ denotes a charged $\pi$ or $K$. The mass of the $\tau$ lepton is measured from a maximum likelihood fit to the $\tau$ pair production cross section data to be $m_{\tau} = (1776.91\pm0.12 ^{+0.10}_{-0.13}$) MeV/$c^2$, which is currently the most precise value in a single measurement.