$\ddot{I}„$ lepton mass measurement at Belle II

Abstract

The reconstruction of tau-pair production, $e^{+}{e}^{-}\to \ddot{I}{„}^{+}\ddot{I}{„}^{-}$, from the subsequent 3-prong ($\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$) and 1-prong ($\ddot{I}{„}^{-}\to {\ell }^{-}\bar{\hat{I}}{½}_{\ell }\hat{I}{½}_{\ddot{I}}„$, $\ddot{I}{„}^{-}\to h^{-}\hat{I}{½}_{\ddot{I}}„$ or $\ddot{I}{„}^{-}\to \ddot{I}{€}^{-}\ddot{I}{€}^0\hat{I}{½}_{\ddot{I}}„$) decays, is presented using 8.8 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data of Belle II at the center-of-mass energy $\sqrt{s}=m_{\hat{I}\yen (4S)}$. The pseudomass technique developed by the ARGUS experiment is used to measure the $\ddot{I}„$-lepton mass $m_{\ddot{I}}„$ in the 3-prong $\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$ decay, resulting in $m_{\ddot{I}}„=1777.28\pm 0.75(stat.)\pm 0.33(sys.)\mathrm{MeV}/{\mathrm{c}}^2$.