LHCb

Abstract:

We search for the decay B⁰ → ρ⁰ρ ⁰ in a data sample of about 227 × 10⁶ Γ(4S) → B B̄ decays collected with the BABAR detector at the PEP-II asymmetric-energy e⁺ e^- collider at SLAC. We find no significant signal and set an upper limit of 1.1 × 10^-6 at 90% C.L. on the branching fraction. As a result, the uncertainty due to penguin contributions on the Cabibbo-Kobayashi-Maskawa unitarity angle α measured in B → ρρ decays is decreased to 11° at 68% C.L. © 2005 The American Physical Society.

Abstract:

We study the decay B^- → J/ΨK ^-π⁺π^- using 117×10⁶ BB̄ events collected at the Y(4S) resonance with the BABAR detector at the PEP-II e⁺e^- asymmetric-energy storage ring. We measure the branching fractions ℬ (B^- → J/ΨK ^-π⁺π^-) = (116±7(stat.) ±9(syst.))×10^-5 and ℬ (B^- → X(3872)K^-) × ℬ (X(3872) → J/Ψπ⁺π ^-) = (1.28±0.41)×10^-5 and find the mass of the X(3872) to be 3873.4±1.4 MeV/c². We search for the h c narrow state in the decay B^- → hcK ^-, hc → J/Ψπ⁺π^- and for the decay B^- → J/ΨD⁰π^-, with D⁰ → K^-π⁺. We set the 90% C.L. limits ℬ(B^- → hcK^-) × ℬ(h c → J/Ψπ⁺π^-)<3. 4×10^-6 and ℬ(B^- → J/ΨD ⁰π^-)<5.2×10^-5. © 2005 The American Physical Society.

Abstract:

We search for the rare flavor-changing neutral-current decay B⁺ → K⁺ νν̄ in a data sample of 82 fb^-1 collected with the BABAR detector at the PEP-II S-factory. Signal events are selected by examining the properties of the system recoiling against either a reconstructed hadronic or semileptonic charged-B decay. Using these two independent samples we obtain a combined limit of ℬ(B⁺ →K⁺ νν̄) ≤ 5.2 × 10^-5 at the 90% confidence level In addition, by selecting for pions rather than kaons, we obtain a limit of ℬ(B⁺ → π⁺ νν̄) < 1.0 × 10^-4 using only the hadronic B reconstruction method. © 2005 The American Physical Society.

Abstract:

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| based on a sample of about 53 700 B̄⁰ → D*⁺ℓ^-ν̄ℓ decays observed by the BABAR detector. We obtain the branching fraction averaged over ℓ = e, μ, B(B̄⁰ → D*⁺ℓ ^-ν̄ℓ) = (4.90 ± 0.07(stat.) -0.35^+0.36(syst.))%. We measure the differential decay rate as a function of w, the relativistic boost γ of the D*⁺ in the B̄⁰ rest frame. By extrapolating dΓ/dw to the kinematic limit w → 1, we extract the product of |V cb| and the axial form factor A1(w = 1). We combine this measurement with a lattice QCD calculation of A1(w = 1) to determine |Vcb) = (38.7 ± 0.3(stat.) ± 1.7(syst.) -1.3^+1.5(theory)) × 10^-3. © 2005 The American Physical Society.

Abstract:

We study the process e⁺e^- → π⁺π ^-π⁺π^-γ, with a hard photon radiated from the initial state. About 60 000 fully reconstructed events have been selected from 89 fb^-1 of BABAR data. The invariant mass of the hadronic final state defines the effective e⁺e^- e ⁺e^- center-of-mass energy, so that these data can be compared with the corresponding direct e⁺e^- measurements. From the 4π -mass spectrum, the cross section for the process e ⁺e^- → π⁺π ^-π⁺π^- is measured for center-of-mass energies from 0.6 to 4.5 GeV. The uncertainty in the cross section measurement is typically 5%. We also measure the cross sections for the final states K ⁺K^-π⁺π^- and K ⁺K^-K⁺K^-. We observe the J/ψ in all three final states and measure the corresponding branching fractions. We search for X(3872) in Jψ(→ μ⁺μ^-) π⁺π^- and obtain an upper limit on the product of the e⁺e^- width of the X(3872) and the branching fraction for X(3872) → Jψπ⁺π^-. © 2005 The American Physical Society.