Precision measurement of the branching fraction for the decay $\psi(2S)\rightarrow\tau^{+}\tau^{-}$

TL;DR

This paper reports a precise measurement of the branching fraction for the decay of $ ext{psi}(2S)$ into tau pairs using a large data sample, confirming lepton universality and determining the total width of $ ext{psi}(2S)$.

Contribution

The study provides an improved measurement of the $ ext{psi}(2S) o au^+ au^-$ branching fraction, consistent with lepton universality, and calculates the total width of $ ext{psi}(2S)$ with reduced uncertainties.

Findings

Branching fraction $ ext{psi}(2S) o au^+ au^-$ measured as (3.240 ± 0.023 ± 0.081)×10⁻³.

Results agree with the sequential lepton hypothesis within one standard deviation.

Total width of $ ext{psi}(2S)$ determined to be (287 ± 9) keV.

Abstract

Using $(2259.3 \pm 11.1)\times10^{6}$ $\psi(2S)$ events acquired with the BESIII detector, the branching fraction of $\psi(2S)\rightarrow\tau^{+}\tau^{-}$ is measured with improved precision to be $\mathcal{B}_{\psi(2S)\rightarrow\tau^{+}\tau^{-}}=(3.240~\pm~0.023~\pm~0.081)\times 10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, which is consistent with the world average value within one standard deviation. This value, along with those for the branching fractions of the $\psi(2S)$ decaying into $e^{+}e^{-}$ and $\mu^{+}\mu^{-}$, is in good agreement with the relation predicted by the sequential lepton hypothesis. Combining the branching fraction values with the leptonic width of the $\psi(2S)$, the total width of the $\psi(2S)$ is determined to be (287 $\pm$ 9) keV.