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CLEO Collaboration

Publications and source records attributed to CLEO Collaboration.

269 records · Page 15Linked to original sources

First Observation of Inclusive $B$ Decays to the Charmed Strange Baryons $Ξ_{c}^{0}$ and $Ξ_{c}^{+}$

Using data collected in the region of the Upsilon(4S) resonance with the CLEO II detector operating at the Cornell Electron Storage Ring CESR, we present the first observation of B mesons decaying into the charmed strange baryons Xi_c0 and Xi_c+. We find 79 +/- 27 Xi_c0 and 125 +/- 28 Xi_c+ candidates from B decays, leading to product branching fractions of BR(Bbar -> Xi_c0 X)BR(Xi_c0 -> Xi- pi+) = (0.144 +/- 0.048 +/- 0.021) x 10^-3 and BR(Bbar -> Xi_c+ X)BR(Xi_c+ -> Xi- pi+ pi+) = (0.453 +/- 0.096 +0.085-0.065) x 10^-3.

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Search for the Decays B^0 -> D^{(*)+} D^{(*)-}

Using the CLEO-II data set we have searched for the Cabibbo-suppressed decays B^0 -> D^{(*)+} D^{(*)-}. For the decay B^0 -> D^{*+} D^{*-}, we observe one candidate signal event, with an expected background of 0.022 +/- 0.011 events. This yield corresponds to a branching fraction of Br(B^0 -> D^{*+} D^{*-}) = (5.3^{+7.1}_{-3.7}(stat) +/- 1.0(syst)) x 10^{-4} and an upper limit of Br(B^0 -> D^{*+} D^{*-}) < 2.2 x 10^{-3} at the 90% CL. For B^0 -> D^{*\pm} D^\mp and B^0 -> D^+ D^-, no significant excess of signal above the expected background level is seen, and we calculate the 90% CL upper limits on the branching fractions to be Br(B^0 -> D^{*\pm} D^\mp) < 1.8 x 10^{-3} and Br(B^0 -> D^+ D^-) < 1.2 x 10^{-3}.

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Search for Neutrinoless $τ$ Decays Involving $π^{0}$ or $η$ Mesons

We have searched for lepton family number violating decays of the $τ$ lepton using final states with an electron or a muon and one or more $π^0$ or $η$ mesons but no neutrinos. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.68 $fb^{-1}$. No evidence for signals was found, resulting in much improved limits on the branching fractions for the one-meson modes and the first upper limits for the two-meson modes.

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Studies of the Cabbibo-Suppressed Decays $D^+ \to π^0 \ell^+ ν$ and $D^+ \to ηe^+ ν_e$

Using 4.8 fb$^{-1}$ of data taken with the CLEO II detector, the branching fraction for the Cabibbo-suppressed decay $D^+\toπ^0\ell^+ν$ measured relative to the Cabibbo favored decay $D^+\to\bar{K^0}\ell^+ν$ is found to be $0.046\pm 0.014\pm 0.017$. Using $V_{cs}$ and $V_{cd}$ from unitarity constraints, we determine $| f_+^π(0)/f_+^K(0)|^2=0.9\pm 0.3\pm 0.3$ We also present a 90% confidence level upper limit for the branching ratio of the decay $D^+ \to ηe^+ν_e$ relative to that for $D^+ \to π^0 e^+ν_e$ of 1.5.

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Limit on the Two-Photon Production of the Glueball Candidate $f_{J}(2220)$ at CLEO

We use the CLEO detector at the Cornell electron-positron storage ring, CESR, to search for the two-photon production of the glueball candidate f_J(2220) in its decay to K_s K_s. We present a restrictive upper limit on the product of the two-photon partial width and the K_s K_s branching fraction. We use this limit to calculate a lower limit on the stickiness, which is a measure of the two-gluon coupling relative to the two-photon coupling. This limit on stickiness indicates that the f_J(2220) has substantial glueball content.

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The Inclusive Decays $B\to D X$ and $B\to D^* X$

We report new measurements of the differential and total branching ratios for inclusive B decay to D^0, D^+ and D^{*+} and the first measurement of the same quantities for inclusive B decay to $D^{*0}$. Here B is the mixture of B_d and B_u from $Υ(4S)$ decay. Furthermore, since more than one charm particle (or antiparticle) of the same kind can be produced in B decay, here ``inclusive B branching ratio'' is used to mean the average number of charm particles and their antiparticles of a certain species produced in B decay. We obtain the following results (the first error is statistical, the second systematic of this analysis, the third is propagated from other measurements): ${\cal B}(B\to D^0 X) = (0.636\pm 0.014\pm 0.019\pm 0.018), {\cal B}(B\to D^+ X) = (0.235\pm 0.009\pm 0.009\pm 0.024), {\cal B}(B\to D^{*0} X) = (0.247\pm 0.012\pm 0.018\pm 0.018), {\cal B}(B\to D^{*+} X) = (0.239\pm 0.011\pm 0.014\pm 0.009)$. The following ratio of branching ratios is not affected by most of the systematic errors: ${\cal B}(B\to D^{*0} X)/{\cal B}(B\to D^{*+} X) = (1.03\pm 0.07\pm 0.09\pm 0.08).$ We also report the first measurement of the momentum-dependent $D^{*0}$ polarization and a new measurement of the $D^{*+}$ polarization in inclusive B decay. Using these measurements and other CLEO results and making some additional assumptions, we calculate the average number of c and $\bar c$ quarks produced in B decay to be $< n_c > = 1.10\pm 0.05$.

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Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance

We have made a first measurement of the lepton momentum spectrum in a sample of events enriched in neutral B's through a partial reconstruction of B0 --> D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the Upsilon(4S) resonance by the CLEO II detector, is compared directly to the inclusive lepton spectrum from all Upsilon(4S) events in the same data set. These two spectra are consistent with having the same shape above 1.5 GeV/c. From the two spectra and two other CLEO measurements, we obtain the B0 and B+ semileptonic branching fractions, b0 and b+, their ratio, and the production ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950 (+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57 +- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes, tau+/tau0.

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Tau Neutrino Helicity from $h^{\pm}$ Energy Correlations

We report a measurement of the magnitude of the tau neutrino helicity from tau-pair events taken with the CLEO detector at the CESR electron-positron storage ring. Events in which each tau undergoes the decay tau -> h nu, with h a charged pion or kaon, are analyzed for energy correlations between the daughter hadrons, yielding |xi| = 2*|h_nu| = 1.03 +/- 0.06 +/- 0.04, with the first error statistical and the second systematic.

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Measurement of the Direct Photon Spectrum in $Υ(1S)$ Decays

Using data taken with the CLEO II detector at the Cornell Electron Storage Ring, we have determined the ratio of branching fractions: $R_γ \equiv Γ(Υ(1S) \rightarrow γgg)/Γ(Υ(1S) \rightarrow ggg) = (2.75 \pm 0.04(stat.) \pm 0.15(syst.))%$. From this ratio, we have determined the QCD scale parameter $Λ_{\overline{MS}}$ (defined in the modified minimal subtraction scheme) to be $Λ_{\overline{MS}}= 233 \pm 11 \pm 59$ MeV, from which we determine a value for the strong coupling constant $α_{s}(M_{Υ(1S)}) = 0.163 \pm 0.002 \pm 0.014$, or $α_{s}(M_{Z}) = 0.110 \pm 0.001 \pm 0.007$.

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Measurement of the Inclusive Semi-electronic $D^0$ Branching Fraction

Using the angular correlation between the $π^+$ emitted in a $D^{*+} \rightarrow D^0 π^+$ decay and the $e^+$ emitted in the subsequent $D^0 \rightarrow Xe^+ν$ decay, we have measured the branching fraction for the inclusive semi-electronic decay of the $D^0$ meson to be: {\cal B}(D^0 \rightarrow X e^+ ν) = [6.64 \pm 0.18 (stat.) \pm 0.29 (syst.)] \%. The result is based on 1.7 fb$^{-1}$ of $e^+e^-$ collisions recorded by the CLEO II detector located at the Cornell Electron Storage Ring (CESR). Combining the analysis presented in this paper with previous CLEO results we find, \frac{{\cal B} (D^0 \rightarrow X e^+ ν)} {{\cal B} (D^0 \rightarrow K^- π^+)} = 1.684 \pm 0.056 (stat.) \pm 0.093(syst.) and \frac{{\cal B}(D\rightarrow K^-e^+ν)} {{\cal B}(D\rightarrow Xe^+ν)} = 0.581 \pm 0.023 (stat.) \pm 0.028(syst.). The difference between the inclusive rate and the sum of the measured exclusive branching fractions (measured at CLEO and other experiments) is $(3.3 \pm 7.2) \%$ of the inclusive rate.

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Measurements of the Ratios ${\cal B}(D_s^+\to η\ell^+ν)/{\cal B}(D_s^+\to ϕ\ell^+ν)$ and ${\cal B}(D_s^+\to η'\ell^+ν)/{\cal B}(D_s^+\to ϕ\ell^+ν)$

Using the CLEO~II detector we measure ${\cal B}(D_s^+\to ηe^+ν)/{\cal B}(D_s^+\to ϕe^+ν) =1.24\pm0.12\pm0.15$, ${\cal B}(D_s^+\to η' e^+ν)/{\cal B}(D_s^+\to ϕe^+ν) =0.43\pm0.11\pm0.07$ and ${\cal B}(D_s^+\to η' e^+ν)/{\cal B}(D_s^+\to ηe^+ν) =0.35\pm0.09\pm0.07$. We find the vector to pseudoscalar ratio, ${\cal B}(D_s^+\to ϕe^+ν)/{\cal B}(D_s^+\to (η+η') e^+ν) =0.60\pm0.06\pm0.06$, which is similar to the ratio found in non strange $D$ decays.

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Observation of a Narrow State Decaying into $Ξ_c^+π^-$

Using data recorded by the CLEO-II detector at CESR, we report the first observation of a narrow state decaying into $Ξ_c^+π^-$. The state has mass difference $M(Ξ_c^+π^-)-M(Ξ_c^+)$ of $178.2\pm0.5\pm1.0$ $\rm{MeV/c^2}$, and a width of $<5.5$ $\rm{MeV/c^2}$ (90\% confidence level limit). The most likely explanation of this new state is that it is the $J=\32$ spin excitation of the $Ξ_c^0$ charmed baryon.

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Observation of the $Ξ_c^+$ Charmed Baryon Decays to $Σ^+ K^-π^+$, $Σ^+ \bar{K}^{*0}$, and $ΛK^-π^+π^+$

We have observed two new decay modes of the charmed baryon $Ξ_c^+$ into $Σ^+ K^-π^+$ and $Σ^+ \bar{K}^{*0}$ using data collected with the CLEO II detector. We also present the first measurement of the branching fraction for the previously observed decay mode $Ξ_c^+\toΛK^-π^+π^+$. The branching fractions for these three modes relative to $Ξ_c^+\toΞ^-π^+π^+$ are measured to be $1.18 \pm 0.26 \pm 0.17$, $0.92 \pm 0.27 \pm 0.14$, and $0.58 \pm 0.16 \pm 0.07$, respectively.

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Observation of the Cabibbo Suppressed Charmed Baryon Decay

We report the observation of the Cabibbo-suppressed decays \lcpkk\ and \lcpphi\ using data collected with the CLEO II detector at CESR. The latter mode, observed for the first time with significant statistics, is of interest as a test of color-suppression in charm decays. We have determined the branching ratios for these modes relative to \lcpkpi\ and compared our results with theory.

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Search for Exclusive Charmless Hadronic B Decays

We have searched for two-body charmless hadronic decays of $B$ mesons. Final states include $ππ$, $K π$, and $KK$ with both charged and neutral kaons and pions; $πρ$, $K ρ$, and $K^*π$; and $Kϕ$, $ K^*ϕ$, and $ϕϕ$. The data used in this analysis consist of 2.6~million $B\bar{B}$~pairs produced at the $Υ(4S)$ taken with the CLEO-II detector at the Cornell Electron Storage Ring (CESR). We measure the branching fraction of the sum of $B^0 \rightarrow π^+π^-$ and $B^0 \rightarrow K^+π^-$ to be $(1.8^{+0.6+0.2}_{-0.5-0.3}\pm0.2) \times 10^{-5}$. In addition, we place upper limits on individual branching fractions in the range from $10^{-4}$ to $10^{-6}$.

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Observation of the Isospin-Violating Decay $D_s^{*+}\to D_s^+π^0$

Using data collected with the CLEO~II detector, we have observed the isospin-violating decay $D_s^{*+}\to D_s^+π^0$. The decay rate for this mode, relative to the dominant radiative decay, is found to be $Γ(D_s^{*+}\to D_s^+π^0)/Γ(D_s^{*+}\to D_s^+γ)= 0.062^{+0.020}_{-0.018}\pm0.022$.

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