Measurement of the branching fraction for $\Upsilon (1S) \to \tau^+ \tau^-$

TL;DR

This paper measures the decay rate of the $5S$ resonance into tau pairs, confirming lepton universality with high precision using data from the CLEO II detector.

Contribution

The study provides a precise measurement of the branching fraction for $5S \to \tau^+ \tau^-$, the first to confirm lepton universality in this decay mode.

Findings

Branching fraction measured as (2.61 ± 0.12 +0.09/-0.13)%

Result consistent with lepton universality

Uses CLEO II detector data

Abstract

We have studied the leptonic decay of the $\Upsilon (1S)$ resonance into tau pairs using the CLEO II detector. A clean sample of tau pair events is identified via events containing two charged particles where exactly one of the particles is an identified electron. We find $B(\Upsilon(1S) \to \tau^+ \tau^-) = (2.61~\pm~0.12~{+0.09\atop{-0.13}})%$. The result is consistent with expectations from lepton universality.