909 research outputs found
Hadronic decays of the D/sub s/ meson
No full textThe D/sub s//sup +/ is the lowest-lying pseudoscalar meson containing charm and anti-strange quarks. Evidence for this state was first reported in 1977, although more recent observations disagree with some of the early results. Since 1983 the weakly decaying D/sub s//sup +/ has been observed in many experiments. Relative branching fractions have been measured for many non-leptonic decay modes, including D/sub s//sup +/ /yields/ /phi//pi//sup +/, /phi//pi//sup +//pi//sup +//pi//sup /minus//, /bar K/*/sup 0/K/sup +/, and f/sub 0/(975)/pi//sup +/. The absolute branching fractions are estimated in high energy e/sup +/e/sup /minus// annihilation from the observed numbers of reconstructed D/sub s//sup +/ decays and the expected D/sub s//sup +/ production cross section. The lowest-lying vector c/bar s/ meson, the D/sub s/*/sup +/, has also been seen in its decay to /gamma/D/sub s//sup +/. Weak decays of the heavy quark and lepton flavors are relevant to the development of the Standard Model of both the electroweak and the strong interactions. Measurements of charmed particle weak decay are useful for determining the parameter of the Standard Model and for testing phenomenological models which include strong effects. 83 refs., 56 figs., 12 tabs
Leptonic decays of the meson and production of orbitally excited D and mesons
No full textThe purely leptonic decays D/sub s/ to mu nu and D/sub s/ to tau nu are studied in a sample of four million hadronic Z decays collected in 1991-1995 with the ALEPH detector at LEP. A linear discriminant analysis is used to measure the branching fraction B(D/sub s/ to mu nu )=(0.64+or-0.08[stat]+or-0.21[syst]+or-0.15[ phi pi ])% (preliminary), where the last uncertainty is from the branching fraction B(D/sub s/ to phi pi ). Within the standard model, this result corresponds to f/sub Ds/=(284+or-18[stat]+or-49[syst]+or-34[ phi pi ]) MeV. Preliminary results are also reported from an investigation of orbitally excited (L=1) charm mesons in Z to cc and bb events. Significant production of such mesons is observed, and the production rates are measured. (10 refs)
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Results on D and D/sub s/ decays from Mark III
No full textThe decays D/sup 0/ /yields/ /pi//sup /minus//e/sup +//nu//sub e/ and D/sup 0/ /yields/ K/sup /minus//e/sup +//nu//sub e/ are observed in a sample of e/sup +/e/sup /minus// /yields/ /psi/(3770) events collected with the Mark III detector at SPEAR. The branching fractions B(D/sup 0/ /yields/ /pi//sup /minus//e/sup +//nu//sub e/) = (0.39/sub /minus/0.11//sup +0.23//plus minus/0.04)% and B(D/sup 0/ /yields/ K/sup /minus//e/sup +//nu//sub e/) = (3.4/plus minus/0.5/plus minus/0.4)% are measured. The ratio of Kobayashi-Maskawa matrix elements V/sub cd//V/sub cs/ /sup 2/ = (0.057/sub /minus/0.015//sup +0.0.38//plus minus/0.005) is obtained under the assumption that the form factors f/sub +//sup K/(0) and f/sub +//sup /pi// are equal. A study of the absolute D/sub s//sup +/ hadronic branching fractions is made by searching for fully reconstructed e/sup +/e/sup /minus// /yields/ D/sub s//sup /asterisk//plus minus//D/sub s//sup /minus plus// events at /radical/s = 4.14 GeV. The 90% confidence level limit B(D/sub s//sup +/ /yields/ /phi//pi//sup +/) < 5.9% is established. 23 refs., 2 figs
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Results on charmed meson decays from Mark III
No full textWe report recent results on charmed meson decays, obtained using the Mark III detector at SPEAR. The first topic discussed is the observation of e/sup +/e/sup -/ ..-->.. D/sub s/D/sub s/* at ..sqrt..s = 4.14 GeV. The D/sub s/* is detected as a peak in the mass distribution recoiling from D/sub s//sup + -/ ..-->.. phi..pi../sup + -/. The mass of the D/sub s/* is found to be (2109.3 +- 2.1 +- 3.1)MeV/c/sup 2/, yielding a D/sub s/*-D/sub s/ mass difference of (137.9 +- 2.1 +- 4.3) MeV/c/sup 2/. The production cross section times branching ratio is also measured. Next, a search for the decay D/sup +/ ..-->.. ..mu../sup +/nu/sub ..mu../ is described. A preliminary upper limit (90% CL) on B(D/sup +/ ..-->.. ..mu../sup +/nu/sub ..mu../) of 8.4 x 10/sup -4/ is obtained, corresponding to an upper limit on the decay constant f/sub D/ of 340 MeV/c/sup 2/. Finally, we present results of a search for the lepton family number violating decay D/sup 0/ ..-->.. ..mu..e. We find B(D/sup 0/ ..-->.. ..mu..e) < 1.5 x 10/sup -4/ at 90% CL
Review of lifetime measurements
No full textThe measurements of the mean lifetime of the tau lepton are reviewed. The conditions for measuring the lifetime at various e+e- colliders are compared and the analysis methods are briefly described. The new developments since the previous Workshop on Tau Lepton Physics are listed. The world average is tau_tau = 290.5 +- 1.0 fs. The LEP experiments dominate this average and have analyzed nearly all of their data. In anticipation of the next era of precision measurements at CLEO and the b factories, the important sources of systematic errors and the treatment of systematic biases are discussed
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