LHCb

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.

Abstract:

We present measurements of the branching fraction and CP-violating asymmetries in the decay B⁰ → f0(980)K s⁰. The results are obtained from a data sample of 123 × 10⁶ Y(4S) → BB̄ decays. From a time-dependent maximum likelihood fit, we measure the branching fraction B(B⁰ → f0(980)(→ π⁺ π^-)K⁰) = (6.0 ± 0.9 ± 0.6 ± 1.2) × 10^-6, the mixing-induced CP violation parameter S = -1.62-0.51^+0.56 ± 0.09 ± 0.04, and the direct CP violation parameter C = 0.27 ± 0.36 ± 0.10 ± 0.07, where the first errors are statistical, the second systematic, and the third due to model uncertainties. We measure the f0 (980) mass and width to be mf(980) = (980.6±4.1± 0.5±4.0)MeV/c² and Γf0(980) = (43-9⁺¹²±3±9) MeV/c², respectively. © 2005 The American Physical Society.