Search Results (28 total)

Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the Ξ_c⁰ decay asymmetry parameter in the decay Ξ_c⁰→Ξ^-π⁺. We find α_Ξc⁰α_Ξ=0.26±0.18(stat)_-0.04^+0.05(syst); using the world average value of α_Ξ=-0.456±0.014 we obtain α_Ξc⁰=-0.56±0.39(stat)_-0.09^+0.10(syst). The physically allowed range of a decay asymmetry parameter is -1<α<+1. Our result prefers a negative value: α_Ξc⁰ is <0.1 at the 90% C.L. The central value occupies the middle of the theoretically expected range but is not yet precise enough to choose between models.

Based on a high statistics e⁺e^-→cc̅ data sample, we report on the inclusive rate for charmed baryons to decay into Λ particles using charm-event tagging. We select e⁺e^-→cc̅ events which have a clear anti-charm tag and measure the Λ content in the hemisphere opposite the tag (charge conjugate modes are implicit). This allows us to determine the product branching fraction B_Λ=B(c→Θ_cX)×B(Θ_c→ΛX), where Θ_c represents a sum over all charmed baryons produced in e⁺e^- fragmentation at sqrt[s]=10.5 GeV, given our specific tags. We obtain B_Λ=(1.87±0.03±0.33)%.

The Λ_c⁺→pK^-π⁺ yield has been measured in a sample of two-jet continuum events containing both a charm tag (“D̅ ”) as well as an antiproton (e⁺e^-→D̅ p̅ X), with the antiproton in the hemisphere opposite the D̅ (measurement of charge conjugate modes is implicit throughout). Under the hypothesis that such selection criteria tag e⁺e^-→D̅ p̅ Λ_c⁺X events, the Λ_c⁺→pK^-π⁺ branching fraction can be determined by measuring the pK^-π⁺ yield in the same hemisphere as the antiprotons in our D̅ p̅ X sample. Three types of D̅ charm tags are used, π_soft^- (from D^*-→D⁰π_soft^-), electrons (from D̅ →Xe^-ν), and fully reconstructed D⁰→K⁺π^- or D^-→K⁺π^-π^- or D_s^-→φπ^-. Combining our results obtained from the three independent charm tags, we obtain B(Λ_c⁺→pK^-π⁺)=(5.0±0.5±1.2)%.

A study of charm fragmentation into D_s^*+ and D_s⁺ in e⁺e^- annihilations at sqrt[s]=10.5 GeV is presented. This study using 4.72±0.05 fb^-1 of CLEO II data reports measurements of the cross sections σ(D_s^*+) and σ(D_s⁺) in momentum regions above x=0.44, where x is the D_s momentum divided by the maximum kinematically allowed D_s momentum. The D_s vector to vector plus pseudoscalar production ratio is measured to be P_V(x(D_s⁺)>0.44)=0.44±0.04.

We search for CP-violating charge asymmetries ( A_CP ) in the B meson decays to K^±π^∓, K^±π⁰, K_S⁰π^±, K^±η^′, and ωπ^±. Using 9.66 million ϒ(4S) decays collected with the CLEO detector, the statistical precision on A_CP is in the range of ±0.12 to ±0.25 depending on decay mode. While CP-violating asymmetries of up to ±0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied.

In a sample of 19×10⁶ produced B mesons, we have observed the decays B→ηK^* and improved our previous measurements of B→η^′K. The branching fractions we measure for these decay modes are B(B⁺→ηK^*+)  =  (26.4_-8.2^+9.6±3.3)×10^-6, B(B⁰→ηK^*0)  =  (13.8_-4.6^+5.5±1.6)×10^-6, B(B⁺→η^′K⁺)  =  (80_-9⁺¹⁰±7)×10^-6, and B(B⁰→η^′K⁰)  =  (89_-16⁺¹⁸±9)×10^-6. We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.

We have studied charmless hadronic decays of B mesons into two-body final states with kaons and pions and observe three new processes with the following branching fractions: B(B→π⁺π^-)  =  (4.3_-1.4^+1.6±0.5)×10^-6, B(B→K⁰π⁰)  =  (14.6_-5.1-3.3^+5.9+2.4)×10^-6, and B(B→K^±π⁰)  =  (11.6_-2.7-1.3^+3.0+1.4)×10^-6. We also update our previous measurements for the decays B→K^±π^∓ and B^±→K⁰π^±.

We report on a study of the invariant mass spectrum of the hadronic system in the decay τ^-→π^-π⁰ν_τ. This study was performed with data obtained with the CLEO II detector operating at the CESR e⁺e^- collider. We present fits to phenomenological models in which resonance parameters associated with the ρ(770) and ρ(1450) mesons are determined. The π^-π⁰ spectral function inferred from the invariant mass spectrum is compared with data on e⁺e^-→π⁺π^- as a test of the conserved vector current theorem. We also discuss the implications of our data with regard to estimates of the hadronic contribution to the muon anomalous magnetic moment.

The resonant structure of the four pion final state in the decay τ→3ππ⁰ν_τ has been analyzed using 4.27 million τ⁺τ^- pairs collected by the CLEO II experiment at the Cornell Electron Storage Ring. A partial wave analysis of the resonant structure of the τ→3ππ⁰ν_τ decay has been performed; the spectral decomposition of the four pion system is dominated by the ωπ and a₁π final states. The mass and width of the ρ^′ resonance have been extracted from a fit to the τ→ωπν_τ spectral function. We have searched for second class currents in the decay τ→ωπν_τ using spin-parity analysis and established an upper limit on the non-vector current contribution.

We present an update of the search for the lepton family number violating decay τ→μγ using 12.6 million τ⁺τ^- pairs collected with the CLEO detector. No evidence of a signal has been found and the corresponding upper limit is B(τ→μγ)<1.1×10^-6 at 90% C.L., significantly smaller than previous experimental limits.

We have used the CLEO II detector to study the multiplicity of charged particles in the decays of B mesons produced at the Υ(4S) resonance. Using a sample of 1.5×10⁶ B meson pairs, we find the mean inclusive charged particle multiplicity to be 10.71±0.02_-0.15^+0.21 for the decay of the pair. This corresponds to a mean multiplicity of 5.36±0.01_-0.08^+0.11 for a single B meson. Using the same data sample, we have also extracted the mean multiplicities in semileptonic and nonleptonic decays. We measure a mean of 7.82±0.05_-0.19^+0.21 charged particles per BB̅ decay when both mesons decay semileptonically. When neither B meson decays semileptonically, we measure a mean charged particle multiplicity of 11.62±0.04_-0.18^+0.24 per BB̅ pair.

We present the first observation of the decay B→J/ψφK. Using 9.6×10⁶ BB̅ meson pairs collected with the CLEO detector, we have observed ten fully reconstructed B→J/ψφK candidates, whereas the estimated background is 0.5±0.2 event. We obtain a branching fraction of B(B→J/ψφK)  =  (8.8_-3.0^+3.5[stat]±1.3[syst])×10^-5. This is the first observed B meson decay requiring the creation of an additional ss̅ quark pair.

Using the CLEO II detector operating at the Cornell Electron Storage Ring (CESR) e⁺e^- collider, we have measured the structure functions in the decay τ^∓→π^∓π⁰π⁰ν_τ, based on a sample corresponding to 4×10⁶ produced τ-pair events. We determine the integrated structure functions, which depend only on the three pion invariant mass, as well as the structure functions differential in the Dalitz plot variables. We extract model independent limits on non-axial-vector contributions from the measured structure functions as less than 16.6% of the total branching fraction, at the 95% confidence level. Separating the non-axial-vector contributions into scalar and vector contributions, we measure that scalars (vectors) contribute with less than 9.4% (7.3%) to the total branching fraction, at the 95% confidence level.

From a data sample of 29058 τ^±→π^±π⁺π^-π⁰ν_τ decays observed in the CLEO detector we derive a 95% confidence upper limit on the tau neutrino mass of 28 MeV.

Using a sample of 3.3×10⁶ Υ(4S)→BB̅ events collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR), we measure B(B→ρlν), |V_ub|, and the partial rate (ΔΓ) in three bins of q²≡(p_B-p_ρ)². We find B(B⁰→ρ^-l⁺ν)=(2.69±0.41_-0.40^+0.35±0.50)×10^-4, |V_ub|=(3.23±0.24_-0.26^+0.23±0.58)×10^-3, ΔΓ(0<q²<7 GeV²/c⁴)=(7.6±3.0_-1.2^+0.9±3.0)×10^-2 ns^-1, ΔΓ(7<q²<14 GeV²/c⁴)=(4.8±2.9_-0.8^+0.7±0.7)×10^-2 ns^-1, and ΔΓ(14<q²<21 GeV²/c⁴)=(7.1±2.1_-1.1^+0.9±0.6)×10^-2 ns^-1. Here, l=e or μ, but not both, and the errors are statistical, systematic, and theoretical. The method is sensitive primarily to B→ρlν decays with leptons in the energy range above 2.3 GeV. Averaging with the previously published CLEO results for B→ρlν, we obtain B(B⁰→ρ^-l⁺ν)=(2.57±0.29_-0.46^+0.33±0.41)×10^-4 and |V_ub|=(3.25±0.14_-0.29^+0.21±0.55)×10^-3.

Using 4.68 fb^-1 of e⁺e^- annihilation data collected with the CLEO II detector at the Cornell Electron Storage Ring, we have studied τ radiative decays τ^-→ν_τμ^-ν̅ _μγ and τ^-→ν_τe^-ν̅ _eγ. For a 10 MeV minimum photon energy in the τ rest frame, the branching fraction for radiative τ decay to a muon or electron is measured to be (3.61±0.16±0.35)×10^-3 or (1.75±0.06±0.17)×10^-2, respectively. The branching fractions are in agreement with standard model theoretical predictions.

We have searched for rare and forbidden decays of the η^′ meson in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb^-1 of e⁺e^- collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring. We find no signals, and set 90% confidence level upper limits of their branching fractions: B(η^′→e⁺e^-η)<2.4×10^-3, B(η^′→e⁺e^-π⁰)<1.4×10^-3, B(η^′→e⁺e^-γ)<0.9×10^-3, and B(η^′→eμ)<4.7×10^-4. We also fit the matrix element of the η^′→π⁺π^-η Dalitz plot with the parametrization |M|²  =  A|1+αy|², where y is a linear function of the kinetic energy of the η, and find Re (α)  =  -0.021±0.025.

Based on a sample corresponding to 4.3×10⁶ produced τ-pair events, we have studied hadronic dynamics in the decay τ^-→ν_τπ^-π⁰π⁰ in data recorded by the CLEO II detector operating at the CESR e⁺e^- collider. The decay is dominated by the process τ^-→ν_τa₁^-(1260), with the a₁^- meson decaying to three pions predominantly via the lowest dimensional (mainly S-wave) ρ^-π⁰ Born amplitude. From model-dependent fits to the Dalitz plot and angular observables in bins of 3π mass, we find significant additional contributions from amplitudes for a₁ decay to σπ, f₀(1370)π, and f₂(1270)π, as well as higher dimensional a₁→ρπ and ρ^′π amplitudes. Notably, the squared σπ amplitude accounts for approximately 15% of the total τ^-→ν_τπ^-π⁰π⁰ rate in the models considered. The data are well described using couplings to these amplitudes that are independent of the 3π mass. These amplitudes also provide a good description for the τ^-→ν_τπ^-π⁺π^- Dalitz plot distributions. We have searched for additional contributions from τ^-→ν_τπ^′-(1300). We place 90% confidence level upper limits on the branching fraction for this channel of between 1.0×10^-4 and 1.9×10^-4, depending on the π^′ decay mode considered. The π^-π⁰π⁰ mass spectrum is parametrized by a Breit-Wigner form with a mass-dependent width which is specified according to the results of the Dalitz plot fits plus an unknown coupling to an a₁→K^*K amplitude. From a χ² fit using this parametrization, we extract the pole mass and width of the a₁, as well as the magnitude of the K^*K coupling. We have also investigated the impact of a possible contribution from the a₁^′(1700) meson on this spectrum. Finally, exploiting the parity-violating angular asymmetry in a₁→3π decay, we determine the signed value of the τ neutrino helicity to be h_ντ=-1.02±0.13 (stat)±0.03 (syst+model), confirming the left-handedness of the τ neutrino.

Using data recorded by the CLEO II detector at the Cornell Electron Storage Ring, we report evidence for two new charmed baryons, one decaying into Ξ_c⁺π⁺π^- via an intermediate Ξ_c^*0 and its isospin partner decaying into Ξ_c⁰π⁺π^- via an intermediate Ξ_c^*+. We measure the mass differences of the two states to be M(Ξ_c⁺π⁺π^-)-M(Ξ_c⁺)  =  348.6±0.6±1.0 MeV, and M(Ξ_c⁰π⁺π^-)-M(Ξ_c⁰)  =  347.2±0.7±2.0 MeV. We interpret these new states as the J^P  =  3 / 2^- Ξ_c1 particles, the charmed-strange analogs of the Λ_c1⁺(2625).

We report measurements of the D⁰, D⁺, and D_s⁺ meson lifetimes using 3.7 fb^-1 of e⁺e^- annihilation data collected near the ϒ(4S) resonance with the CLEO detector. The measured lifetimes of the D⁰, D⁺, and D_s⁺ mesons are 408.5±4.1_-3.4^+3.5 fs, 1033.6±22.1_-12.7^+9.9 fs, and 486.3±15.0_-5.1^+4.9 fs. The precisions of these lifetimes are comparable to those of the best previous measurements, and the systematic errors are very different. In a single experiment we find that the ratio of the D_s⁺ and D⁰ lifetimes is 1.19±0.04.

We have observed four fully reconstructed B⁰→D^*+D^*- candidates in 5.8×10⁶ ϒ(4S)→BB̅ decays recorded with the CLEO detector. The background is estimated to be 0.31±0.10 events. The probability that the background could produce four or more signal candidates with the observed distribution among D^*+ and D^*- decay modes is 1.1×10^-4. The measured decay rate, B(B⁰→D^*+D^*-)  =  [6.2_-2.9^+4.0(stat)±1.0(syst)]×10^-4, is large enough for this decay mode to be of interest for the measurement of a time-dependent CP asymmetry.

We have searched for five decay modes of the τ lepton that simultaneously violate lepton and baryon number: τ^-→p̅ γ, τ^-→p̅ π⁰, τ^-→p̅ η, τ^-→p̅ 2π⁰, and τ^-→p̅ π⁰η. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring. The integrated luminosity of the data sample is 4.7 fb^-1, corresponding to the production of 4.3×10⁶ τ⁺τ^- events. No evidence is found for any of the decays, resulting in much improved upper limits on the branching fractions for the two-body decays and first upper limits for the three-body decays.

We report the first observation of two narrow charmed strange baryons decaying to Ξ_c⁺γ and Ξ_c⁰γ, respectively, using data from the CLEO II detector at the Cornell Electron Storage Ring. We interpret the observed signals as the Ξ_c^+′ (c{su}) and Ξ_c^0′ (c{sd}), the symmetric partners of the well-established antisymmetric Ξ_c⁺ (c[su]) and Ξ_c⁰ (c[sd]). The mass differences M(Ξ_c^+′)-M(Ξ_c⁺) and M(Ξ_c^0′)-M(Ξ_c⁰) have been measured to be 107.8±1.7±2.5 and 107.0±1.4±2.5 MeV/c², respectively.

We consider a lattice-gas model with an infinite pairwise nonconvex total interaction of the form V(r)=J/r²+Acos(2k_Far+φ)/r. This one-dimensional interaction might account, for example, for adsorption of alkaline elements on W(112) and Mo(112). The first term describes the effective dipole-dipole interaction, while the other one the indirect (oscillatory) interaction; J, A, and φ are the model parameters, whereas k_F stands for the wave vector of electrons at the Fermi surface and a is a lattice constant. We search for the (periodic) ground states. To solve this difficult problem we have applied an interesting numerical method to accelerate the convergence of Fourier series. A competition between dipole-dipole and indirect interactions turns out to be very important. We have found that the reduced chemical potential μ/J versus A/J phase diagrams contain a region 0.1⩽A/J⩽1.5 dominated by only several phases with periods up to nine lattice constants. Of course, the resulting sequence of phases (for fixed A/J) depends on the wave vector k_F and the phase shift φ. The remaining phase diagram reveals a complex structure of usually long periodic phases. We conjecture, based on the above results, that quasi-one-dimensional surface states might be responsible for experimentally observed ordered phases at the (112) surface of tungsten and molybdenum. © 1996 The American Physical Society.

It is found that the results of Jarić and Birman of possible lower-symmetry phases arising from the A15 structure are not correct and, by using the Landau approach to symmetry changes at continuous phase transitions the corrected results for symmetry changes at ^*X→ and ^*R→ points of the Brillouin zone are presented.