Reconstruction and classification of tau lepton decays with ILD

Abstract

Tau-lepton decays with up to two $\ddot{I}{€}^0$'s in the final state, $\ddot{I}{„}^{+}\to \ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$, $\ddot{I}{}^{+}(\ddot{I}{€}^{+}\ddot{I}{€}^0)\bar{\hat{I}}{½}_{\ddot{I}}„$, $a_1^{+}(\ddot{I}{€}^{+}\ddot{I}{€}^0\ddot{I}{€}^0)\bar{\hat{I}}{½}_{\ddot{I}}„$, are used to study the performance of the barrel part of the silicon-tungsten electromagnetic calorimeter (Si-W ECAL) of the International Large Detector (ILD) at the future $e^{+}-e^{-}$ International Linear Collider. A correct reconstruction of the tau decay mode is crucial for constraining the tau spin state and measuring the Higgs boson CP state in $H\to \ddot{I}{„}^{+}\ddot{I}{„}^{-}$ decays. About 95% of $\ddot{I}{€}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$ and 90% of $\ddot{I}{}^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$ and $a_1^{+}\bar{\hat{I}}{½}_{\ddot{I}}„$ decays from $e^{+}{e}^{-}\to Z^0\to \ddot{I}{„}^{+}\ddot{I}{„}^{-}$ reaction at $e^{\pm }$-beam energy of 125 GeV are correctly reconstructed. In a smaller ILD detector, with Si-W ECAL radius reduced by about 20% these numbers degrade by at most 2%. The $\ddot{I}{€}^0$ mass resolution stays below 10%. Since the failures in the tau-lepton reconstruction are mainly due to photons, the increase of the ILD magnetic field from 3.5 T to 4 T does not bring any significant improvement.