Precision measurement of the ratio $\mathcal{B}$$\left(\Upsilon(3S)\rightarrow\tau^+\tau^-\right)/\mathcal{B}$$\left(\Upsilon(3S)\rightarrow\mu^+\mu^-\right)$

Abstract

The BaBar collaboration has measured the ratio $R_{\tau\mu}^{\Upsilon(3S)}=\mathcal{B}(\Upsilon(3S)\rightarrow\tau^+\tau^-)/\mathcal{B}(\Upsilon(3S)\rightarrow\mu^+\mu^-)$ with a high level of precision. This measurement utilized a 28 fb$^{-1}$ dataset collected at a center-of-mass energy of 10.355 GeV. The measured ratio, $R_{\tau\mu}^{\Upsilon(3S)}$, is measured to be $R_{\tau\mu}^{\Upsilon(3S)}=0.966\pm0.008_{\textrm{stat}}\pm0.014_{\textrm{syst}}$. This value is within 2 standard deviations of the standard model prediction $R_{\tau\mu}^{\Upsilon(3S)}$=0.9948. The new measurement is approximately a factor of 6$\times$ more precise than the only prior measurement. This increased precision is in part due to a more complete analysis of the radiative tail in the $\Upsilon(3S)$ decay, in addition to a significant increase in statistics.