Tau decays to five and seven charged particles and the tau neutrino mass

Benjamin Glenn Bylsma, Purdue University

Abstract

The production of $\tau$-lepton pairs in e$\sp+$e$\sp-$ collisions at 29 GeV has been used to study the inclusive $\tau$ decay into five and seven charged particles. The results obtained in this analysis are based on a data sample corresponding to a total integrated luminosity of 300 pb$\sp{-1}$. Thirteen events are observed in which the $\tau$ decays to five charged particles giving a branching ratio of B($\tau$ $\to$ 5$\pi\sp\pm\nu\sb\tau$ + n$\gamma$) = (10.2 $\pm$ 2.9) $\times$ 10$\sp{-4}$. Six of these events contain neutral energy consistent with a single $\pi\sp{o}$. With this interpretation the exclusive branching ratios are measured to be B($\tau$ $\to$ 5$\pi\sp\pm\nu\sb\tau$) = (5.1 $\pm$ 2.0) $\times$ 10$\sp{-4}$ and B($\tau$ $\to$ 5$\pi\sp\pm\pi\sp{o}\nu\sb\tau$) = (5.1 $\pm$ 2.2) $\times$ 10$\sp{-4}$. No $\tau$ decays to seven charged particles were observed giving an upper limit on the branching ratio of B($\tau$ $\to$ 7$\pi\sp\pm\nu\sb\tau$ + n$\gamma$) $<$ 1.9 $\times$ 10$\sp{-4}$ at the 90% confidence level. This data was used to look for $\tau$ $\to$ K$\sp{o}$3$\pi\sp\pm\nu\sb\tau$ + n$\gamma$. No K$\sp{o}$'s were found in the sample of 13 events, yielding an upper limit on the branching ratio of B($\tau$ $\to$ K$\sp{o}$3$\pi\sp\pm\nu\sb\tau$ + n$\gamma$) $<$ 2.1 $\times$ 10$\sp{-3}$ at the 90% confidence level. The 5$\pi\sp\pm\pi\sp{o}$ events were also used to place limits on $\tau$ decays involving one or two $\eta$'s. The 90% confidence level upper limits are found to be B($\tau$ $\to$ $\eta$3$\pi\sp\pm$n$\pi\sp{o}\nu\sb\tau$) $<$ 0.005 and B($\tau$ $\to$ $\eta\eta\pi\sp\pm$n$\pi\sp{o}\nu\sb\tau$) $<$ 0.007 (n $\ge$ 0). The hadronic mass spectrum of the five-prong $\tau$ events was used to place an upper limit on the mass of the $\tau$ neutrino. At the 95% confidence level the upper limit is M$\sb\nu\sb\tau$ $<$ 76MeV/c$\sp2$.

Degree

Ph.D.

Advisors

Koltick, Purdue University.

Subject Area

Particle physics

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