Measurement of the 𝜏 Neutrino Helicity and Michel Parameters in Polarized 𝑒⁺⁢𝑒⁻ Collisions

Here, we present a new measurement of the 𝜏 neutrino helicity ℎ_{𝜈_𝜏} and the 𝜏 Michel parameters 𝜌, 𝜂, 𝜉, and the product 𝛿⁢𝜉. The analysis exploits the highly polarized SLC electron beam to extract these quantities directly from a measurement of the 𝜏 decay spectra, using the 1993–1995 SLD data sample of 4328 𝑒⁺⁢𝑒⁻ →𝑍⁰ →𝜏⁺⁢𝜏⁻ events. From the decays 𝜏 →𝜋⁢𝜈_𝜏 and 𝜏 →𝜌⁢𝜈_𝜏 we obtain a combined value ℎ_{𝜈_𝜏} = −0.93 ±0.10 ±0.04. The leptonic decay channels yield combined values of 𝜌 = 0.72 ±0.09 ±0.03, 𝜉 = 1.05 ±0.35 ±0.04, and 𝛿⁢𝜉 = 0.88 ±0.27 ±0.04.. Authors: Abe, K.; Abe, K.; Akagi, T.; Allen, N. J.; Ash, W. W.. DOE Contract: AC02-76SF00515. Subjects: 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS