Mass and spin-parity character of the Τ-meson

Abstract

In this paper we present analyses of 41 Τ- and Τ′-meson decay events. Since the emulsion density was accurately known, and an improved range-energy curve is available, aQ-value for the Τ-decay was obtained which is more precise than that available heretofore. It is 75.08 ± 0.20 MeV. Analysis to determine the character of the Τ-meson was made by comparing the experimental data with the 5 spin-parity combinations that lead to unique energy and angular distributions. It is found on employing a χ2 test that there is a probability of 18% that the χ2 for the (0,−) choice may exceed that observed, whereas the next most probable choice, (3, −), yields a probability of only 2.8%. The data could not distinguish between the (0,−) and (2,−) states of the Τ-meson. The Τ′/Τ ratio observed is 0.25 ± 0.12, which is consistent with the hypothesis of charge independence. The energy distribution of the π+-meson in the Τ′-decay is consistent with a decay scheme Τt → π+ + 2π0, and an associated electron pair also confirms this supposed mode of decay.