2018/05/26 by V. Cherepanov, W. Lohmann, Cherepanov, Vladimir +1
Physics and Astronomy · #Particle physics theoretical and experimental studies #Particle Detector Development and Performance #High-Energy Particle Collisions Research
paper · pdf · doi:10.48550/arxiv.1805.10552
In this paper a general method to measure the longitudinal polarization of τ lepton in the process pp → Z0 → ττ is described. The method of optimal observable allows to distinguish between the τ lepton helicity states with maximum possible sensitivity. The optimal observable for the main τ decay modes (e/μνν, πν, ρν, a1ν) that can be identified by CMS or ATLAS detectors is described. The analyzing power for τ polarization can be further gained by taking into account a correlation between longitudinal spin states of τ+ and τ-. The theoretical systematic uncertainty on the τ polarization measured using the τ→ 3πν decays is estimated to be (ΔPτ)model = (1.41 ± 1.37)× 10-4. This value is approximately 50 times smaller than the best uncertainty on τ polarization measurement given by combination of all LEP results. An approach to propagate the measured τ polarization averaged over the Z0 lineshape and parton density functions to the electroweak parameters is also discussed.