Performance study of the polarization measurement in decays at CEPC by using the template method

Y. Y. Du; J. X. Ma; B. Li

doi:10.1140/epjp/s13360-023-04523-y

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2024 Impact factor 2.9

EPJ PLUS - Condensed Matter and Complex Systems

Eur. Phys. J. Plus (2023) 138: 887
https://doi.org/10.1140/epjp/s13360-023-04523-y

Regular Article

Performance study of the $τ$ $\tau$ polarization measurement in $Z \to π ν$ $\mathrm Z\rightarrow \pi \nu$ decays at CEPC by using the template method

Y. Y. Du, J. X. Ma and B. Li^c

College of Nuclear Equipment and Nuclear Engineering, Yantai University, 264005, Yantai, Shandong, China

^c boli@ytu.edu.cn

Received: 23 August 2023
Accepted: 25 September 2023
Published online: 6 October 2023

Abstract

The Circular Electron Positron Collider (CEPC) is designed to operate at around 91.2 GeV as a Z factory. It will produce close to one trillion Z bosons, including the vast amount of $τ$ $\tau$ leptons in the leptonic Z decays. In this study, the $τ$ $\tau$ polarization has been studied with the CEPC Monte Carlo (MC) samples around the Z resonance through the decay channel $τ \to π ν_{τ}$ $\tau \rightarrow \pi \nu _{\tau }$ . Assuming the $τ$ $\tau$ lepton decays conforming to V-A theory, the $τ$ $\tau$ polarization parameter, $P_{τ}$ $P_{\tau }$ , can be fitted out from the reconstructed data by using a template method in which the templates are based on the linear combinations of kinematic spectra of positive helicity $τ$ $\tau$ and negative helicity $τ$ $\tau$ . Based on the statistic of $τ \to π ν_{τ}$ $\tau \rightarrow \pi \nu _{\tau }$ which is expected to reach $10^{9}$ $$10^9$$ at CEPC, the statistical uncertainty is estimated to be about $10^{- 6}$ $10^{-6}$ , which means that $τ$ $\tau$ polarization measurement will no longer be limited by statistics. In this study, the systematic errors which mainly arise from the physical modelling and detector effects are also investigated based on the latest world average values and CEPC detector concept. A conservative estimation of the systematic error is discussed for the $τ$ $\tau$ polarization in $τ \to π ν_{τ}$ $\tau \rightarrow \pi \nu _{\tau }$ at CEPC in this study.

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© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2023. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

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Performance study of the τ polarization measurement in Z→πν decays at CEPC by using the template method

Conference announcements

Performance study of the $τ$ $\tau$ polarization measurement in $Z \to π ν$ $\mathrm Z\rightarrow \pi \nu$ decays at CEPC by using the template method