Search

We report the results of a study of the three-prong-decay mode of the tau in data taken with the DELCO detector at the SLAC e/sup +/e/sup -/ storage ring PEP. We determine the total three-prong branching ratio to be B(3) = (12.1 +- 0.5 +- 1.2)% and the exclusive branching ratios B(tau..--> pi../sup +/..pi../sup -/..pi../sup + -/..nu..) = (5.0 +- 1 .0)% and B(tau..--> pi../sup +/..pi../sup -/..pi../sup + -/..pi../sup 0/..nu..) = (6 .0 +- 1.2)%, respectively. The data with three charged pions allow for the determination of the mass and width of the A/sub 1/ resonance as M/sub A//sub 1/ = 1056 +- 20 +- 15 MeV and GAMMA/sub a//sub 1/ = 476/sub -/120/sup +132/ +- 5 4 MeV.

We have studied inclusive D/sup asteriskplus-or-minus/ production using the DELCO detector at PEP. Our technique involved kaon identification in the momentum range above 3.2 GeV/c using a threshold gas Cerenkov counter. This leads to a model-independent upper limit on D/sup 0/-D-bar /sup 0/ mixing of 8.1% (90% confidence level). We also have measured the charm fragmentation function, which peaks at xequivalentP/sub D/(/(E/sub beam//sup 2/-M* /sup 2/)/sup 1/2/ of 0.56 +- 0.06(stat.), and the total cross section for D( production, sigma(D/sup asteriskplus-or-minus/) = 0.140 +- 0.021(stat.) +- 0.032(syst.) nb (x > 0.3, with radiative correction).

In the reaction e/sup +/e/sup -/..-->..psi''(3770), events containint either one or two electrons have been observed originating in semileptonic decays of D mesons. A comparison of these samples provides a determination of the branching ratios: b(D/sup 0/..-->..Xe..nu..) ..Xe..nu..)22.0 -2.2$(per-cent)=. These values imply that the ratio of D/sup 0/ and D/sup +/ lifetimes is tau(D/sup +/)/tau(D/sup 0/)>4.3 (at 95% confidence level).

The electron energy spectrum in the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\psi}}^{\ensuremath{'}\ensuremath{'}}(3770)\ensuremath{\rightarrow}{e}^{\ifmmode\pm\else\textpm\fi{}}+(g2 \mathrm{charged}\mathrm{particles})$ has been used to determine the $D(56%{D}^{0}+44%{D}^{+})$ semileptonic branching ratio. Assuming the Glashow-Iliopoulos-Maiani model, it is found that the inclusive branching ratio is $b(D\ensuremath{\rightarrow}\mathrm{Xe}\ensuremath{\nu})=0.080\ifmmode\pm\else\textpm\fi{}0.015$ and the state $X$ is dominated by $K$ and $K\ensuremath{\pi}$. The fraction of $K\ensuremath{\pi}e\ensuremath{\nu}$ is (37 \ifmmode\pm\else\textpm\fi{} 16)% if the $K\ensuremath{\pi}$ system is entirely ${K}^{*}(890)$, or (55 \ifmmode\pm\else\textpm\fi{} 21)% if the $K\ensuremath{\pi}$ system is nonresonant. Within the assumptions of the analysis, the $D$ lifetime is calculated to be (2.5 \ifmmode\pm\else\textpm\fi{} 1.6) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}13}$ sec.

A sample of events enriched with b b production is obtained with the DELCO detector at PEP and is used to measure the mean multiplicity and spectra of charged particles in bottom-quark jets. Bottom-quark jets are found to be significantly softer and more spherical than jets in general hadronic events.

Inclusive electrons have been studied in hadronic events from e/sup +/e/sup -/ annihilation at 29 GeV. The cross section is measured as sigma(e/sup +/e/sup -/..-->..e/sup + -/X) = 35.8 +- 4.6 pb in the momentum range 0.5 = 0.78 +- 0.05 and = 0.69 +- 0.06. No evidence of anomalous electron production is observed.

A measurement of the D/sup 0/ lifetime using the impact-parameter method is presented. The D/sup 0/ sample is obtained from identified D/sup asteriskplus-or-minus/ decays in e/sup +/e/sup -/ annihilations into hadrons at center-of-mass energy of 29 GeV. The maximum-likelihood method used is found to be insensitive to the specific choice of cuts and uncertainties in backgrounds, giving the D/sup 0/ lifetime of (4.6 +- 1.5 (statistical)/sub -0.5//sup +0.6/(systematic)) x 10/sup -13/ sec. The consistency and bias of the method are checked. Combining the measurement with the semileptonic branching ratio of D/sup 0/, we estimate the semileptonic decay rate of D/sup 0/ to be (1.6 +- 0.6) x 10/sup 11/ sec/sup -1/. The corresponding value of the effective charm-quark mass is found to be consistent with the typical constituent mass of charm quark.

Results are reported from a study of the impact parameters of electrons in hadronic events produced at the PEP ${e}^{+}{e}^{\ensuremath{-}}$ storage ring. Electrons in hadronic events are produced by bottom and charm decay and their impact parameters show hadrons containing bottom quarks to have a lifetime of ${1.16}_{\ensuremath{-}0.34}^{+0.37}$(stat.) \ifmmode\pm\else\textpm\fi{}0.23 (syst.) psec. This result is used to constrain elements of the Kobayashi-Maskawa mixing matrix.

On the basis of a sample of 41 events of the type e/sup +/e/sup -/ ..-->.. e/sup asterisk/X/sup - +/ (X not = e) and no observed photons, we have observed a clear signal of the decay tau/sup -/ ..-->.. ..pi../sup -/..nu../sub tau/. We measure the branching ratio for this decay to be b/sub ..pi../ = 0.080 +- 0.032 +- 0.013 and for the decay tau/sup -/ ..-->.. ..mu../sup -/nu-bar/sub ..mu../..nu../sub tau/, b/sub ..mu../ systematic. Both measurements agree with theoretical values derived under the assumption that the tau decays via the standard weak current.

We report a measurement of the branching ratios for two decay modes of the tau lepton: R/sub B/(tau/sup + -/..-->..K/sup + -/K/sup - +/..pi../sup + -/..nu../sub tau/) = (0.22/sub -0.11//sup +0.17/)% and R/sub B/(tau/sup + -/..-->..k/sup + -/..pi../sup - +/..pi../sup + -/(..pi../sup 0/ )..nu../sub tau/) = (0.22/sub -0.13//sup +0.16/)%. The separation of these channels is accomplished in the DELCO detector by use of a gas Cerenkov counter to identify fast kaons. The invariant-mass distribution of the k/sup + -/K/sup - +/..pi../sup + -/ system has been used to set an upper bound on the tau neutrino mass of 157 MeV at 95% confidence level.

We report final results on prompt electron production in hadronic events from e/sup +/e/sup -/ annihilations at ..sqrt..s = 29 GeV, obtained with the DELCO detector at the SLAC storage ring PEP. We find the semielectronic branching ratios of charm and bottom quarks to be B(c..-->..se/sup +/..nu../sub e/) = (11.6/sub -0.9/ /sup +1.1/)% and B(b..-->..ce/sup -/nu-bar/sub e/) = (14.9/sub -1.9/ /sup +2.2/)% respectively. These results, from the complete data set, are consistent with an earlier analysis of partial data and indicate hard fragmentation functions for both c and b quarks, with mean values = 0.59 +- 0.04 and = 0.72 +- 0.05. The errors indicated here are a combination of statistical and systematic uncertainties.