Search Results (29 total)

We present results from a numerical simulation of the two-dimensional Euclidean Wess-Zumino model. In the continuum the theory possesses N=1 supersymmetry. The lattice model we employ was analyzed by Golterman and Petcher, who gave a perturbative proof that the continuum supersymmetric Ward identities are recovered without fine-tuning in the limit of vanishing lattice spacing. Our simulations demonstrate the existence of important non-perturbative effects in finite volumes which modify these conclusions. It appears that in certain regions of parameter space the vacuum state can contain solitons corresponding to field configurations which interpolate between different classical vacua. In the background of these solitons supersymmetry is partially broken and a light fermion mode is observed. At fixed coupling the critical mass separating phases of broken and unbroken supersymmetry appears to be volume dependent. We discuss the implications of our results for continuum supersymmetry breaking.

We study the two-dimensional Wess-Zumino model with extended N=2 supersymmetry on the lattice. The lattice prescription we choose has the merit of preserving exactly a single supersymmetric invariance at finite lattice spacing a. Furthermore, we construct three other transformations of the lattice fields under which the variation of the lattice action vanishes to O(ga²) where g is a typical interaction coupling. These four transformations correspond to the two Majorana supercharges of the continuum theory. We also derive lattice Ward identities corresponding to these exact and approximate symmetries. We use dynamical fermion simulations to check the equality of the mass gaps in the boson and fermion sectors and to check the lattice Ward identities. At least for weak coupling we see no problems associated with a lack of reflection positivity in the lattice action and find good agreement with theory. At strong coupling we provide evidence that problems associated with a lack of reflection positivity are evaded for small enough lattice spacing.

We have measured the CP asymmetry A_CP≡[Γ(b→sγ)-Γ(b̅ →s̅ γ)]/[Γ(b→sγ)+Γ(b̅ →s̅ γ)] to be A_CP  =  (-0.079±0.108±0.022) (1.0±0.030), implying that, at 90% confidence level, A_CP lies between -0.27 and +0.10. These limits rule out some extreme non-standard-model predictions, but are consistent with most, as well as with the standard model.

Using 13.7 fb^-1 of data recorded by the CLEO detector at the Cornell Electron Storage Ring, we investigate the spectrum of charmed baryons which decay into Λ_c⁺π^-π⁺ and are more massive than the Λ_c⁺(2625) baryon. We find evidence for two new states: one is broad and has an invariant mass roughly 480 MeV above that of the Λ_c⁺ baryon; the other is narrow with an invariant mass of 596±1±2 MeV above the Λ_c⁺ mass.

The τ decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(τ^-→2π^-π⁺3π⁰ν_τ)  =  (2.2±0.3±0.4)×10^-4 and B(τ^-→3π^-2π⁺π⁰ν_τ)  =  (1.7±0.2±0.2)×10^-4. A search for substructure in these decays shows that they are saturated by intermediate states with η or ω mesons. We present the first observation of the decay τ^-→2π^-π⁺ων_τ and the branching fraction is measured to be (1.2±0.2±0.1)×10^-4. The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.

The CLEO experiment at the CESR collider has used 13.7 fb^-1 of data to search for the production of the Ω_c⁰ (css ground state) in e⁺e^- collisions at sqrt[s]≃10.6 GeV. The modes used to study the Ω_c⁰ are Ω^-π⁺, Ω^-π⁺π⁰, Ξ^-K^-π⁺π⁺, Ξ⁰K^-π⁺, and Ω^-π⁺π⁺π^-. We observe a signal of 40.4±9.0(stat) events at a mass of 2694.6±2.6(stat)±1.9(syst) MeV/c², for all modes combined.

We report results of a search for B→τν in a sample of 9.7×10⁶ charged B meson decays. We exclusively reconstruct the companion B̅ decay to suppress background. We set an upper limit on the branching fraction B(B→τν)<8.4×10^-4 at 90% confidence level. We also establish B(B^±→K^±νν̅ )<2.4×10^-4 at 90% confidence level.

We analyze 9.7×10⁶ BB̅ pairs recorded with the CLEO detector to determine the production ratio of charged to neutral B-meson pairs produced at the ϒ(4S) resonance. We measure the rates for B⁰→J/ψK^(*)0 and B⁺→J/ψK^(*)+ decays and use the world-average B-meson lifetime ratio to extract the relative widths f_+- / f₀₀  =  Γ(ϒ(4S)→B⁺B^-) / Γ(ϒ(4S)→B⁰B̅ ⁰)  =  1.04±0.07(stat)±0.04(syst). With the assumption that f_+-+f₀₀  =  1, we obtain f₀₀  =  0.49±0.02(stat)±0.01(syst) and f_+-  =  0.51±0.02(stat)±0.01(syst). This production ratio and its uncertainty apply to all exclusive B-meson branching fractions measured at the ϒ(4S) resonance.

We report the first observation of exclusive decays of the type B→D^*NN̅ X, where N is a nucleon. Using a sample of 9.7×10⁶BB̅ pairs collected with the CLEO detector operating at the Cornell Electron Storage Ring, we measure the branching fractions B(B⁰→D^*-pp̅ π⁺)  =  (6.5_-1.2^+1.3±1.0)×10^-4 and B(B⁰→D^*-pn̅ )  =  (14.5_-3.0^+3.4±2.7)×10^-4. Antineutrons are identified by their annihilation in the CsI electromagnetic calorimeter.

The Λ_c⁺ lifetime is measured using 9.0 fb^-1 of e⁺e^- annihilation data collected on or just below the ϒ(4S) resonance with the CLEO II.V detector at CESR. Using an unbinned maximum likelihood fit, the Λ_c⁺ lifetime is measured to be 179.6±6.9(stat)±4.4(syst) fs. The precision of this colliding beam measurement is comparable to other measurements, which are based on fixed-target experiments, with different systematic uncertainties.

Using data recorded with the CLEO II and CLEO II.V detector configurations at the Cornell Electron Storage Rings, we report the first observation and mass measurement of the Σ_c^*+ charmed baryon, and an updated measurement of the mass of the Σ_c⁺ baryon. We find M(Σ_c^*+)-M(Λ_c⁺)  =  (231.0±1.1±2.0)  MeV, and M(Σ_c⁺)-M(Λ_c⁺)  =  (166.4±0.2±0.3)  MeV, where the errors are statistical and systematic, respectively.

We report on a search for a supersymmetric B̃ meson with mass between 3.5 and 4.5 GeV/c² using 4.52 fb^-1 of integrated luminosity produced at sqrt[s]=10.52 GeV, just below the e⁺e^-→BB̅ threshold, and collected with the CLEO detector. We find no evidence for a light scalar bottom quark.

Color-suppressed decays of B mesons to final states with ψ(2S) mesons have been observed with the CLEO detector. The branching fractions for the decays B⁺→ψ(2S)K⁺, B⁺→ψ(2S)K^*(892)⁺, B⁰→ψ(2S)K⁰, and B⁰→ψ(2S)K^*(892)⁰ are measured to be (7.8±0.7±0.9)×10^-4, (9.2±1.9±1.2)×10^-4, (5.0±1.1±0.6)×10^-4, and (7.6±1.1±1.0)×10^-4, respectively, where the first uncertainty is statistical and the second is systematic. The first measurement of the longitudinal polarization fraction is extracted from the angular analysis of the B→ψ(2S)K^*(892) candidates: Γ_L/Γ=0.45±0.11±0.04. Our measurements of the decays B⁰→ψ(2S)K⁰ and B⁺→ψ(2S)K^*(892)⁺ are first observations.

Using a sample of 9.7×10⁶ BB̅ meson pairs collected with the CLEO detector, we study B decays to the χ_c1 and χ_c2 charmonia states, which are reconstructed via their radiative decays to J/ψ. We first measure the branching fraction for inclusive χ_c1 production in B decays to be B(B→χ_c1X)=(4.14±0.31±0.40)×10^-3, where the first uncertainty is statistical and the second one is systematic. We derive the branching fractions for direct χ_c1 and χ_c2 production in B decays by subtracting the known contribution of the decay chain B→ψ(2S)X with ψ(2S)→χ_c1,2γ. We obtain B[B→χ_c1(direct)X]=(3.83±0.31±0.40)×10^-3. No statistically significant signal for χ_c2 production is observed in either case. Using the Feldman-Cousins approach, we determine the 95% confidence intervals to be [0.2,2.0]×10^-3 for B(B→χ_c2X), [0.0,1.7]×10^-3 for B[B→χ_c2(direct)X], and [0.00,0.44] for the ratio Γ[B→χ_c2(direct)X]/Γ[B→χ_c1(direct)X]. We also measure the branching ratio Γ[B→χ_c2(direct)X_s]/Γ[B→χ_c1(direct)X_s] for different X_s configurations by reconstructing B decays into exclusive final states with J/ψ, γ, a kaon, and up to four pions. For all the X_s configurations, we observe a strong χ_c1 signal yet no statistically significant χ_c2 signal. We discuss how our results compare with theoretical predictions in different models of charmonium production.

In a sample of 9.66×10⁶BB̅ pairs collected with the CLEO detector we make the first observation of B decays to an η_c and a kaon. We measure branching fractions B(B⁺→η_cK⁺)  =  (0.69_-0.21^+0.26±0.08±0.20)×10^-3 and B(B°→η_cK°)  =  (1.09_-0.42^+0.55±0.12±0.31)×10^-3, where the first error is statistical, the second is systematic, and the third is from the η_c branching fraction uncertainty. From these we extract the η_c decay constant in the factorization approximation, f_ηc  =  335±75 MeV. We also search for B decays to a χ_c0 and a kaon. No evidence for a signal is found and we set 90% C.L. upper limits: B(B⁺→χ_c0K⁺)<4.8×10^-4 and B(B°→χ_c0K°)<5.0×10^-4.

This article describes improved measurements by CLEO of the B⁰→D_s⁺D^*- and B⁰→D_s^*+D^*- branching fractions, and first evidence for the decay B⁺→D_s^(*)+D^**0, where D^**0 represents the sum of the D₁(2420)⁰, D₂^*(2460)⁰, and D₁(j=1/2)⁰ L=1 charm meson states. Also reported is the first measurement of the D_s^*+ polarization in the decay B⁰→D_s^*+D^*-. A partial reconstruction technique, employing only the fully reconstructed D_s⁺ and slow pion π_s^- from the D^*-→D⁰π_s^- decay, enhances sensitivity. The observed branching fractions are B(B⁰→D_s⁺D^*-)=(1.10±0.18±0.10±0.28)%, B(B⁰→D_s^*+D^*-)=(1.82±0.37±0.24±0.46)%, and B(B⁺→D_s^(*)+D^**0)=(2.73±0.78±0.48±0.68)%, where the first error is statistical, the second systematic, and the third is the uncertainty in the D_s⁺→φπ⁺ branching fraction. The measured D_s^*+ longitudinal polarization, Γ_L/Γ=(50.6±13.9±3.6)%, is consistent with the factorization prediction of 54%.

Using 13.4 fb^-1 of data collected with the CLEO detector at the Cornell Electron Storage Ring, we have observed 300 events for the two-photon production of ground-state pseudoscalar charmonium in the decay η_c→K_S⁰K^∓π^±. We have measured the η_c mass to be [2980.4±2.3 (stat)±0.6 (syst)] MeV and its full width as [27.0±5.8 (stat)±1.4 (syst)] MeV. We have determined the two-photon partial width of the η_c meson to be [7.6±0.8 (stat)±0.4 (syst)±2.3 (br)] keV, with the last uncertainty associated with the decay branching fraction.

We report results of searches for charmless hadronic B meson decays to pseudoscalar( π^±, K^±, π⁰, or K_S⁰)-vector( ρ, K^*, or ω) final states. By using 9.7×10⁶ BB̅ pairs collected with the CLEO detector, we report the first observation of B^-→π^-ρ⁰, B̅ ⁰→π^±ρ^∓, and B^-→π^-ω, which are expected to be dominated by hadronic b→u transitions. The measured branching fractions are (10.4_-3.4^+3.3±2.1)×10^-6, (27.6_-7.4^+8.4±4.2)×10^-6, and (11.3_-2.9^+3.3±1.4)×10^-6, respectively. Branching fraction upper limits are set for all of the other decay modes investigated.

We search for the decay of the B⁰ meson into a pair of leptons in the suppressed channels B⁰→e⁺e^-, B⁰→μ⁺μ^- and in the lepton number violating channel B⁰→e^±μ^∓ in a sample of 9.7×10⁶ BB̅ pairs recorded by CLEO detector. No signal is found, and the following upper limits on the branching fractions are established: B(B⁰→e⁺e^-)<8.3×10^-7, B(B⁰→μ⁺μ^-)<6.1×10^-7, B(B⁰→e^±μ^∓)<15×10^-7 at 90% confidence level. A new lower limit on the Pati-Salam leptoquark mass M_LQ>27 TeV is established at 90% confidence level.

Using a sample of 4.7 fb^-1 integrated luminosity accumulated with the CLEO II detector at the Cornell Electron Storage Ring (CESR), we investigate the mass spectrum and resonant structure in τ^-→K^-π⁺π^-ν_τ decays. We measure the relative fractions of K₁(1270) and K₁(1400) resonances in these decays, as well as the K₁ masses and widths. Our fitted K₁ resonances are somewhat broader than previous hadroproduction measurements, and in agreement with recent CERN LEP results from tau decay. The larger central value of our measured width supports models which attribute the small τ^-→K^-π⁺π^-ν_τ branching fraction to larger K₁ widths than are presently tabulated. We also determine the K_a-K_b mixing angle θ_K.

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)%.

We present a study of three B⁰ decay modes useful for time-dependent CP asymmetry measurements. From a sample of 9.7×10⁶ BB̅ meson pairs collected with the CLEO detector, we have reconstructed B⁰→J/ψK_S⁰, B⁰→χ_c1K_S⁰, and B⁰→J/ψπ⁰ decays. The latter two decay modes have been observed for the first time. We describe a K_S⁰→π⁰π⁰ detection technique and its application to the reconstruction of the decay B⁰→J/ψK_S⁰. Combining the results obtained using K_S⁰→π⁺π^- and K_S⁰→π⁰π⁰ decays, we determine B(B⁰→J/ψK⁰)=(9.5±0.8±0.6)×10^-4, where the first uncertainty is statistical and the second one is systematic. We also obtain B(B⁰→χ_c1K⁰)=(3.9_-1.3^+1.9±0.4)×10^-4 and B(B⁰→J/ψπ⁰)=(2.5_-0.9^+1.1±0.2)×10^-5.

The decays B⁰→D^*+D^*-, B⁰→D^*±D^∓ and B⁰→D⁺D^- are studied in 9.7×10⁶ Υ(4S)→BB̅ decays accumulated with the CLEO detector. We determine B(B⁰→D^*+D^*-)=(9.9_-3.3^+4.2[stat]±1.2[syst])×10^-4 and limit B(B⁰→D^*±D^∓)<6.3×10^-4 and B(B⁰→D⁺D^-)<9.4×10^-4 at 90% confidence level (C.L.). We also perform the first angular analysis of the B⁰→D^*+D^*- decay and determine that the CP-even fraction of the final state is greater than 0.11 at 90% C.L. Future measurements of the time dependence of these decays may be useful for the investigation of CP violation in neutral B meson decays.

We present a search for direct CP violation in B^±→J/ψK^± and B^±→ψ(2S)K^± decays. In a sample of 9.7×10⁶ BB̅ meson pairs collected with the CLEO detector, we have fully reconstructed 534 B^±→J/ψK^± and 120 B^±→ψ(2S)K^± decays with very low background. We have measured the CP-violating charge asymmetry to be [+1.8±4.3(stat)±0.4(syst)]% for B^±→J/ψK^± and [+2.0±9.1(stat)±1.0(syst)]% for B^±→ψ(2S)K^±.

We have studied exclusive, radiative B meson decays to charmless mesons in 9.7×10⁶ BB̅ decays accumulated with the CLEO detector. We measure B(B⁰→K^*0(892)γ)  =  (4.55_-0.68^+0.72±0.34)×10^-5 and B(B⁺→K^*+(892)γ)  =  (3.76_-0.83^+0.89±0.28)×10^-5. We have searched for CP asymmetry in B→K^*(892)γ decays and measure A_CP  =  +0.08±0.13±0.03. We report the first observation of B→K₂^*(1430)γ decays with a branching fraction of (1.66_-0.53^+0.59±0.13)×10^-5. No evidence for the decays B→ργ and B⁰→ωγ is found and we limit B(B→(ρ/ω)γ)/B(B→K^*(892)γ)<0.32 at 90% C.L.