Reconstruction and classification of tau lepton decays with ILD

TL;DR

This study evaluates the performance of the ILD detector's electromagnetic calorimeter in reconstructing tau lepton decays, crucial for Higgs boson CP measurements, showing high reconstruction efficiency and stable performance under design variations.

Contribution

It demonstrates the effectiveness of the ILD Si-W ECAL in accurately reconstructing tau decay modes, essential for future Higgs and tau physics analyses.

Findings

Approximately 95% of $ au^+ o ar{ u}_ au ext{ and } ho^+ ext{ decays are correctly reconstructed.

Reconstruction efficiency remains high even with a 20% reduction in detector size.

Photon-related failures limit tau reconstruction accuracy, unaffected by increased magnetic field.

Abstract

Tau-lepton decays with up to two $\pi^0$'s in the final state, $\tau^+ \to \pi^+ \bar{\nu}_\tau$, $\rho^+ (\pi^+\pi^0) \bar{\nu}_\tau$, $a^+_1 (\pi^+\pi^0\pi^0) \bar{\nu}_\tau$, 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 $H\to \tau^+\tau^-$ decays. About 95% of $\pi^+ \bar{\nu}_\tau$ and 90% of $\rho^+\bar{\nu}_\tau$ and $a^+_1\bar{\nu}_\tau$ decays from $e^+e^-\to Z^0\to \tau^+\tau^-$ 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 $\pi^0$ 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.