Reconstruction and classification of tau lepton decays with ILD

T. H. Tran; V. Balagura; V. Boudry; J.-C. Brient; H. Videau

doi:10.1140/epjc/s10052-016-4315-2

EPJ

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2016) 76: 468
https://doi.org/10.1140/epjc/s10052-016-4315-2

Special Article - Tools for Experiment and Theory

Reconstruction and classification of tau lepton decays with ILD

T. H. Tran^*, V. Balagura, V. Boudry, J.-C. Brient and H. Videau

Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Université Paris-Saclay, 91128, Palaiseau, France

^* e-mail: trong.hieu.tran@llr.in2p3.fr

Received: 21 October 2015
Accepted: 10 August 2016
Published online: 20 August 2016

Abstract

Tau lepton decays with up to two $\pi ^0$ s in the final state – $\tau ^+ \rightarrow \pi ^+ \bar{\nu }_\tau$ , $\rho ^+ (\pi ^+\pi ^0) \bar{\nu }_\tau$ , and $\mathrm {a}_{1}^{+}(\pi ^+\pi ^0\pi ^0) \bar{\nu }_\tau$ – are used to study the performance of the barrel region of the silicon-tungsten electromagnetic calorimeter (Si-W ECAL) of the International Large Detector (ILD) at the future $\mathrm{e}^{+} \mathrm{e}^{-}$ International Linear Collider. Correct reconstruction of the tau decay mode is crucial for constraining the spin state of tau lepton and measuring the Higgs boson CP state in $\mathrm{H}{}{} \rightarrow \tau ^+\tau ^-$ decays. We find that about 95 % of $\pi ^+ \bar{\nu }_\tau$ , and 90 % of $\rho ^+\bar{\nu }_\tau$ and $\mathrm {a}_{1}^{+}\bar{\nu }_\tau$ decays produced by the $\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow {\mathrm{Z}^{0}}^*\rightarrow \tau ^+\tau ^-$ process at an $e^\pm$ beam energy of 125 GeV are correctly reconstructed. In a smaller ILD detector, with the inner Si-W ECAL radius reduced by about 20 %, these efficiencies are reduced by at most 2 %. The $\pi ^0$ mass resolution remains below 10 %. Since failures in tau lepton reconstruction are mainly due to photons, an increase of the ILD magnetic field from 3.5 to 4 T does not bring any significant improvement.