726 research outputs found

    A High Statistics Measurement of the Lambdac+ Lifetime

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    A high statistics measurement of the Lambdac+ lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat.) +/- 2.5 (syst.) fs from 8034 +/- 122 Lambdac -> pKpi decays represents a significant improvement over the present world average.Comment: Submitted to Physical Review Letter

    Search for CP Violation in the decays D+ -> K_S pi+ and D+ -> K_S K+

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    A high statistics sample of photo-produced charm from the FOCUS(E831) experiment at Fermilab has been used to search for direct CP violation in the decays D+->K_S pi+ and D+ -> K_S K+. We have measured the following asymmetry parameters relative to D+->K-pi+pi+: A_CP(K_S pi+) = (-1.6 +/- 1.5 +/- 0.9)%, A_CP(K_S K+) = (+6.9 +/- 6.0 +/- 1.5)% and A_CP(K_S K+) = (+7.1 +/- 6.1 +/- 1.2)% relative to D+->K_S pi+. The first errors quoted are statistical and the second are systematic. We also measure the relative branching ratios: \Gamma(D+->\bar{K0}pi+)/\Gamma(D+->K-pi+pi+) = (30.60 +/- 0.46 +/- 0.32)%, \Gamma(D+->\bar{K0}K+)/\Gamma(D+->K-pi+pi+) = (6.04 +/- 0.35 +/- 0.30)% and \Gamma(D+->\bar{K0}K+)/\Gamma(D+->\bar{K0}pi+) = (19.96 +/- 1.19 +/- 0.96)%.Comment: 4 pages, 3 figure

    New FOCUS results on charm mixing and CP violation

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    We present a summary of recent results on CP violation and mixing in the charm quark sector based on a high statistics sample collected by photoproduction experiment FOCUS (E831 at Fermilab). We have measured the difference in lifetimes for the D0D^0 decays: D0→K−π+D^0 \to K^-\pi^+ and D0→K−K+D^0 \to K^-K^+. This translates into a measurement of the yCPy_{CP} mixing parameter in the \d0d0 system, under the assumptions that K−K+K^-K^+ is an equal mixture of CP odd and CP even eigenstates, and CP violation is negligible in the neutral charm meson system. We verified the latter assumption by searching for a CP violating asymmetry in the Cabibbo suppressed decay modes D+→K−K+π+D^+ \to K^-K^+\pi^+, D0→K−K+D^0 \to K^-K^+ and D0→π−π+D^0 \to \pi^-\pi^+. We show preliminary results on a measurement of the branching ratio Γ(D∗+→π+(K+π−))/Γ(D∗+→π+(K−π+))\Gamma(D^{*+}\to \pi^+ (K^+\pi^-))/\Gamma(D^{*+}\to \pi^+ (K^-\pi^+)).Comment: 9 pages, 6 figures, requires espcrc2.sty. Presented by S.Bianco at CPConf2000, September 2000, Ferrara (Italy). In this revision, fixed several stylistic flaws, add two significant references, fixed a typo in Tab.

    A measurement of branching ratios of D+D^+ and Ds+D^+_s hadronic decays to four-body final states containing a KSK_S

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    We have studied hadronic four-body decays of D+D^+ and Ds+D^+_s mesons with a KSK_S in the final state using data recorded during the 1996-1997 fixed-target run at Fermilab high energy photoproduction experiment FOCUS. We report a new branching ratio measurement of Γ(D+→KSK−π+π+)/Γ(D+→KSπ+π+π−)=0.0768±0.0041±0.0032\Gamma(D^+\to K_S K^-\pi^+\pi^+)/\Gamma(D^+\to K_S \pi^+\pi^+\pi^-)=0.0768\pm0.0041\pm0.0032. We make the first observation of three new decay modes with branching ratios Γ(D+→KSK+π+π−)/Γ(D+→KSπ+π+π−)=0.0562±0.0039±0.0040\Gamma(D^+\to K_S K^+\pi^+\pi^-)/\Gamma(D^+\to K_S \pi^+\pi^+\pi^-)=0.0562\pm0.0039\pm0.0040, \Gamma(D^+\to\K_S K^+ K^-\pi^+)/\Gamma(D^+\to K_S \pi^+\pi^+\pi^-)=0.0077\pm0.0015\pm0.0009, and Γ(Ds+→KSK+π+π−)/Γ(Ds+→KSK−π+π+)=0.586±0.052±0.043\Gamma(D^+_s\to K_S K^+\pi^+\pi^-)/\Gamma(D^+_s\to K_S K^-\pi^+\pi^+)=0.586\pm0.052\pm0.043, where in each case the first error is statistical and the second error is systematic.Comment: 4 pages, 1 table, 2 figures, submitted to Physical Review Letter

    The Target Silicon Detector for the FOCUS Spectrometer

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    We describe a silicon microstrip detector interleaved with segments of a beryllium oxide target which was used in the FOCUS photoproduction experiment at Fermilab. The detector was designed to improve the vertex resolution and to enhance the reconstruction efficiency of short-lived charm particles.Comment: 18 pages, 14 figure

    Search for CP violation in D0 and D+ decays

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    A high statistics sample of photoproduced charm particles from the FOCUS (E831) experiment at Fermilab has been used to search for CP violation in the Cabibbo suppressed decay modes D+ to K-K+pi+, D0 to K-K+ and D0 to pi-pi+. We have measured the following CP asymmetry parameters: A_CP(K-K+pi+) = +0.006 +/- 0.011 +/- 0.005, A_CP(K-K+) = -0.001 +/- 0.022 +/- 0.015 and A_CP(pi-pi+) = +0.048 +/- 0.039 +/- 0.025 where the first error is statistical and the second error is systematic. These asymmetries are consistent with zero with smaller errors than previous measurements.Comment: 12 pages, 4 figure

    Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-

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    Using the FOCUS spectrometer with photon beam energies between 20 and 160 \gev, we confirm the existence of a diffractively photoproduced enhancement in K+K−K^+K^- at 1750 \mevcc with nearly 100 times the statistics of previous experiments. Assuming this enhancement to be a single resonance with a Breit-Wigner mass shape, we determine its mass to be 1753.5±1.5±2.31753.5\pm 1.5\pm 2.3 \mevcc and its width to be 122.2±6.2±8.0122.2\pm 6.2\pm 8.0 \mevcc. We find no corresponding enhancement at 1750 \mevcc in K∗KK^*K, and again neglecting any possible interference effects we place limits on the ratio Γ(X(1750)→K∗K)/Γ(X(1750)→K+K−)\Gamma (X(1750) \to K^*K)/\Gamma (X(1750) \to K^+K^-). Our results are consistent with previous photoproduction experiments, but, because of the much greater statistics, challenge the common interpretation of this enhancement as the ϕ(1680)\phi (1680) seen in e+e−e^+e^- annihilation experiments.Comment: 10 pages, 5 figure
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