Search Results (53 total)

Using the CLEO detector at the Cornell Electron Storage Ring, we have studied the distribution of kinematic variables in the decay Λ_c⁺→Λe⁺ν_e. By performing a four-dimensional maximum likelihood fit, we determine the form factor ratio, R=f₂/f₁=-0.31±0.05(stat)±0.04(syst), the pole mass, M_pole=[2.21±0.08(stat)±0.14(syst)]  GeV/c², and the decay asymmetry parameter of the Λ_c⁺, α_Λc=-0.86±0.03(stat)±0.02(syst), for ⟨q²⟩=0.67 (GeV/c²)². We compare the angular distributions of the Λ_c⁺ and Λ̅ _c^- and find no evidence for CP violation: A_Λc=(α_Λc+α_{Λ̅ c}) / (α_Λc-α_{Λ̅ c})=0.00±0.03(stat)±0.01(syst)±0.02, where the third error is from the uncertainty in the world average of the CP-violating parameter, A_Λ, for Λ→pπ^-.

We report on a search for CP violation in the decay of D⁰ and D̅ ⁰ to K_S⁰π⁺π^-. The data come from an integrated luminosity of 9.0   fb^-1 of e⁺e^- collisions at sqrt[s]≈10  GeV recorded with the CLEO II.V detector. The resonance substructure of this decay is well described by ten quasi-two-body decay channels plus a small nonresonant component. We observe no evidence for CP violation in the amplitudes that describe the decay D⁰→K_S⁰π⁺π^-.

We report on determinations of |V_ub| resulting from studies of the branching fraction and q² distributions in exclusive semileptonic B decays that proceed via the b→u transition. Our data set consists of the 9.7×10⁶ BB̅ meson pairs collected at the Υ(4S) resonance with the CLEO II detector. We measure B(B⁰→π^-l⁺ν)=(1.33±0.18±0.11±0.01±0.07)×10^-4 and B(B⁰→ρ^-l⁺ν)=(2.17±0.34_-0.54^+0.47±0.41±0.01)×10^-4, where the errors are statistical, experimental systematic, systematic due to residual form-factor uncertainties in the signal, and systematic due to residual form-factor uncertainties in the cross-feed modes, respectively. We also find B(B⁺→ηl⁺ν)=(0.84±0.31±0.16±0.09)×10^-4, consistent with what is expected from the B→πlν mode and quark model symmetries. We extract |V_ub| using light-cone sum rules for 0<~q²<16 GeV² and lattice QCD for 16 GeV²<~q²<q_max². Combining both intervals yields |V_ub|=(3.24±0.22±0.13_-0.39^+0.55±0.09)×10^-3 for πlν, and |V_ub|=(3.00±0.21_-0.35-0.38^+0.29+0.49±0.28)×10^-3 for ρlν, where the errors are statistical, experimental systematic, theoretical, and ρlν form-factor shape, respectively. Our combined value from both decay modes is |V_ub|=(3.17±0.17_-0.17-0.39^+0.16+0.53±0.03)×10^-3.

We present final measurements of 13 charmless hadronic B decay modes from the CLEO experiment. The decay modes include the ten ππ, Kπ, and KK final states and new limits on dibaryonic final states, pp̅ , pΛ̅ , and ΛΛ̅ , as well as a new determination of the ratio B(B→DK)/B(B→Dπ). The results are based on the full CLEO II and CLEO III data samples totalling 15.3 fb^-1 at the Υ(4S), and supercede previously published results.

Using data collected on the Υ(4S) resonance and the nearby continuum by the CLEO detector at the Cornell Electron Storage Ring, we have searched for the semileptonic decay of B mesons to ep̅ inclusive final states. We obtain an upper limit for b→c decays of B(B→p̅ e^-ν̅ _eX)<5.9×10^-4. For the b→u decay, we find an upper limit of B(B^-→pp̅ e^-ν̅ _e)<1.2×10^-3 based on a V-A model, while a phase space model gives an upper limit of B(B^-→pp̅ e^-ν̅ _e)<5.2×10^-3. All upper limits are measured at the 90% confidence level.

Based on a measurement of high momentum η^′ production in B decays, we determine the charmless inclusive B→η^′X_nc branching fraction in the lab-frame momentum interval 2.0<P_η^′<2.7 GeV/c. Using 9.7×10⁶BB̅ pairs collected at the Υ(4S) center-of-mass energy with the CLEO II and II.V detector configurations, we find B(B→η^′X_nc)=[4.6±1.1±0.4±0.5]×10^-4 in the 2.0<P_η^′<2.7 GeV/c momentum range, where the uncertainties are statistical, systematic, and from subtraction of background from B decays to charm, respectively.

Using 9.1 fb^-1 of e⁺e^- data collected at the Υ(4S) with the CLEO detector using the Cornell Electron Storage Ring, measurements are reported for both the branching fractions and the helicity amplitudes for the decays B^-→D^*0ρ^- and B⁰→D^*+ρ^-. The fraction of longitudinal polarization in B⁰→D^*+ρ^- is found to be consistent with that in B⁰→D^*+l^-ν̅ at q²=M_ρ², indicating that the factorization approximation works well. The longitudinal polarization in the B^- mode is similar. The measurements also show evidence of nontrivial final-state interaction phases for the helicity amplitudes.

From electron-positron collision data collected with the CLEO detector operating at Cornell Electron Storage Ring near sqrt[s]=10.6  GeV, improved measurements of the branching fractions for τ decays into three explicitly identified hadrons and a neutrino are presented as B(τ^-→π^-π⁺π^-ν_τ)=(9.13±0.05±0.46)%, B(τ^-→K^-π⁺π^-ν_τ)=(3.84±0.14±0.38)×10^-3, B(τ^-→K^-K⁺π^-ν_τ)=(1.55±0.06±0.09)×10^-3, and B(τ^-→K^-K⁺K^-ν_τ)<3.7×10^-5 at 90% C.L., where the uncertainties are statistical and systematic, respectively.

We measure the primary lepton momentum spectrum in B̅ →Xlν̅ decays, for p_l>~1.5 GeV/c in the B rest frame. From this, we calculate various moments of the spectrum. In particular, we find R₀≡∫_{1.7 GeV}(dΓ/dE_sl)dE_l/∫_{1.5 GeV}(dΓ/dE_sl)dE_l=0.6187±0.0014_stat±0.0016_sys and R₁≡∫_{1.5 GeV}E_l(dΓ/dE_sl)dE_l/∫_{1.5 GeV}(dΓ/dE_sl)dE_l=(1.7810±0.0007_stat±0.0009_sys) GeV. We use these moments to determine non-perturbative parameters governing the semileptonic width. In particular, we extract the heavy quark expansion parameters Λ̅ =(0.39±0.03_stat±0.06_sys±0.12_th) GeV and λ₁=(-0.25±0.02_stat±0.05_sys±0.14_th) GeV². The theoretical constraints used are evaluated through order 1/M_B³ in the non-perturbative expansion and β₀α_s² in the perturbative expansion. We use these parameters to extract |V_cb| from the world average of the semileptonic width and find |V_cb|=(40.8±0.5_Γsl±0.4_{(λ1,Λ̅ )exp}±0.9_th)×10^-3. In addition, we extract the short range b-quark mass m_b^1S=(4.82±0.07_exp±0.11_th) GeV/c². Finally, we discuss the implications of our measurements for the theoretical understanding of inclusive semileptonic processes.

Using the CLEO II detector at CESR, we measure the η^′ energy spectra in Υ(1S) decays that we compare with models of the η^′g^*g form factor. This form factor, especially at large η^′ energies, may provide an explanation of the large rate for B→X_sη^′. Our data do not support a large anomalous coupling at higher q² and thus the large η^′ rate remains a mystery, possibly requiring a non-standard-model explanation.

Using 13.8   fb^-1 of data collected at or just below the Υ(4S) with the CLEO detector, we report the result of a search for the flavor changing neutral current process D⁰→γγ. We observe no significant signal for this decay mode and determine 90% confidence level upper limits on the branching fractions B(D⁰→γγ)/B(D⁰→π⁰π⁰)<0.033 and B(D⁰→γγ)<2.9×10^-5.

In the standard model, the charged current of the weak interaction is governed by a unitary quark mixing matrix that also leads to CP violation. Measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements is essential to searches for new physics, either through the structure of the CKM matrix, or a departure from unitarity. We determine the CKM matrix element |V_cb| using a sample of 3×10⁶ BB̅ events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed B⁰→D^*+lν̅ and B^-→D^*0lν̅ decays as a function of w, the boost of the D^* in the B rest frame, and from this we obtain the differential decay rate dΓ/dw. By extrapolating dΓ/dw to w=1, the kinematic end point at which the D^* is at rest relative to the B, we extract the product |V_cb|F(1), where F(1) is the form factor at w=1. We find |V_cb|F(1)=0.0431±0.0013(stat)±0.0018(syst). We combine |V_cb|F(1) with theoretical results for F(1) to determine |V_cb|=0.0469±0.0014(stat)±0.0020(syst)±0.0018(theor). We also integrate the differential decay rate over w to obtain B(B⁰→D^*+lν̅ )=(6.09±0.19±0.40)% and B(B^-→D^*0lν̅ )=(6.50±0.20±0.43)%.

Using data collected by the CLEO III detector at CESR, we report on the first observation of the decays Λ_c⁺→Λπ⁺π⁺π^-π⁰ and Λ_c⁺→Λωπ⁺. The branching fractions are measured relative to the pK^-π⁺ mode; we find B(Λ_c⁺→Λπ⁺π⁺π^-π⁰)/B(Λ_c⁺→pK^-π⁺)=0.36±0.09(stat)±0.09(syst) and B(Λ_c⁺→Λωπ⁺)/B(Λ_c⁺→pK^-π⁺)=0.24±0.06(stat)±0.06(syst). We also observe a small excess of events in Λ_c⁺→Ληπ⁺, η→π⁺π^-π⁰ from which we find B(Λ_c⁺→Ληπ⁺)/B(Λ_c⁺→pK^-π⁺)=0.41±0.17±0.10 with a corresponding limit of <0.65% at 90% confidence level. This rate is consistent with previous measurements of Λ_c⁺→Ληπ⁺, η→γγ. We find that the combined branching fractions for Λ_c⁺→Λωπ⁺ and Λ_c⁺→Ληπ⁺ comprise (87±13)% of the total Λ_c⁺→Λπ⁺π⁺π^-π⁰ rate. We set an upper limit on B(Λ_c⁺→Λπ⁺π⁺π^-π⁰)/B(Λ_c⁺→pK^-π⁺) for non-ω and non-η modes of 0.13 at 90% confidence level.

Using the combined CLEO II and CLEO II.V data sets of 9.1   fb^-1 at the ϒ(4S), we measure properties of ψ mesons produced directly from decays of the B meson, where “B” denotes an admixture of B⁺, B^-, B⁰, and B̅ ⁰, and “ψ” denotes either J/ψ(1S) or ψ(2S). We report first measurements of ψ polarization in B→ψ(direct)X: α_ψ(1S)=-0.30_-0.06^+0.07±0.04 and α_ψ(2S)=-0.45_-0.19^+0.22±0.04. We also report improved measurements of the momentum distributions of ψ produced directly from B decays, correcting for measurement smearing. Finally, we report measurements of the inclusive branching fraction for B→ψX and B→χ_c1X.

In e⁺e^- collisions using the CLEO detector, we have studied the decay of the D⁰ to the final state K_S⁰π⁺π^- with the initial flavor of the D⁰ tagged by the decay D^*+→D⁰π⁺. We use the Dalitz technique to measure the resonant substructure in this final state and clearly observe ten different contributions by fitting for their amplitudes and relative phases. We observe a K^*(892)⁺π^- component which arises from doubly Cabibbo suppressed decays or D⁰-D⁰̅ mixing.

We report on a search for charmless hadronic B decays to the three-body final states K_S⁰h⁺π^-, K⁺h^-π⁰, K_S⁰h⁺π⁰ (h^± denotes a charged pion or kaon), and their charge conjugates, using 13.5   fb^-1 of integrated luminosity produced near sqrt[s]=10.6   GeV, and collected with the CLEO detector. We observe the decay B→K⁰π⁺π^- with a branching fraction (50_-9⁺¹⁰(stat.)±7(syst.))×10^-6 and the decay B→K^*+(892)π^- with a branching fraction (16_-5⁺⁶(stat.)±2(syst.))×10^-6.

Using data collected by the CLEO detector in the Υ(4S) region, we report new measurements of the exclusive decays of B mesons into final states of the type Λ_c⁺p̅ n(π), where n=0,1,2,3. We find signals in modes with one, two and three pions and an upper limit for the two-body decay Λ_c⁺p̅ . We also make the first measurements of exclusive decays of B mesons to Σ_cp̅ n(π), where n=0,1,2. We find signals in modes with one and two pions and an upper limit for the two-body decay Σ_cp̅ . Measurements of these modes shed light on the mechanisms involved in B decays to baryons.

Using 13.53   fb^-1 of CLEO data, we have measured the ratios of the branching fractions R_e⁺,R_μ⁺ and the combined branching fraction ratio R_l⁺, defined by R_l⁺=[B(D⁺→K̅ ^*0l⁺ν_l)]/[B(D⁺→K^-π⁺π⁺)]. We find R_e⁺=0.74±0.04±0.05, R_μ⁺=0.72±0.10±0.05, and R_l⁺=0.74±0.04±0.05, where the first and second errors are statistical and systematic, respectively. The known branching fraction B(D⁺→K^-π⁺π⁺) leads to B(D⁺→K̅ ^*0e⁺ν_e)=(6.7±0.4±0.5±0.4)%, B(D⁺→K̅ ^*0μ⁺ν_μ)=(6.5±0.9±0.5±0.4)%, and B(D⁺→K̅ ^*0l⁺ν_l)=(6.7±0.4±0.5±0.4)%, where the third error is due to the uncertainty in B(D⁺→K^-π⁺π⁺).

The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E_γ=2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.

Using 13.3 fb^-1 of e⁺e^- data recorded with the CLEO II and CLEO II.V detector configurations at CESR, we have searched for f_J(2220) decays to K_S⁰K_S⁰ in untagged two-photon interactions. We report an upper limit on the product of the two-photon partial width and the branching fraction, Γ_γγB(f_J(2220)→K_S⁰K_S⁰), of less than 1.1 eV at the 95% confidence level; systematic uncertainties are included. This data set is four times larger than that used in the previous CLEO publication.

Using the CLEO detector at the Cornell Electron Storage Ring we have observed the Ω_c⁰ (css ground state) in the decay Ω_c⁰→Ω^-e⁺ν_e. We find a signal of 11.4±3.8(stat) events. The probability that we have observed a background fluctuation is 7.6×10^-5. We measure B(Ω_c⁰→Ω^-e⁺ν_e)·σ(e⁺e^-→Ω_c⁰X)=(42.2±14.1(stat)±5.7(syst))   fb and R=Γ(Ω_c⁰→Ω^-π⁺) / Γ(Ω_c⁰→Ω^-eν_e)=00.41±0.19(stat)±0.04(syst). This is the first statistically significant observation of an individual decay mode of the Ω_c⁰ in e⁺e^- annihilation and the first example of a baryon decaying via β emission, where no quarks from the first generation participate in the reaction.

We have searched for lepton flavor violating decays of the τ lepton with one or two K_S⁰ mesons in the final state. The data used in the search were collected with the CLEO II and II.V detectors at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 13.9 fb^-1 at the Υ(4S) resonance. No evidence for signals were found; therefore, we have set 90% confidence level (C.L.) upper limits on the branching fractions B(τ^-→e^-K_S⁰)<9.1×10^-7, B(τ^-→μ^-K_S⁰)<9.5×10^-7, B(τ^-→e^-K_S⁰K_S⁰)<2.2×10^-6, and B(τ^-→μ^-K_S⁰K_S⁰)<3.4×10^-6. These represent significantly improved upper limits on the two-body decays and first upper limits on the three-body decays.

The ratio of charged and neutral B meson production at the Υ(4S), f_+-/f₀₀, is measured through the decays B̅ →D^*l^-ν̅ _l, reconstructed using a partial reconstruction method where the D^* is detected only through a pion daughter from the decay D^*→Dπ. Using data collected by the CLEO II detector, the charged and neutral B decays are measured in such a way that their ratio is independent of the decay model, limited mainly by the uncertainty in the relative efficiency for detecting neutral and charged pions. This measurement yields the ratio of production fractions times the ratio of semileptonic branching fractions, f_+-b₊/f₀₀b₀. Assuming that b₊/b₀ is equal to the lifetime ratio τ₊/τ₀ and using the world average value of τ₊/τ₀ as input, we obtain f_+-/f₀₀=1.058±0.084±0.136.