Search Results (324 total)

We present a combined measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_cb| and of the parameters ρ², R₁(1), and R₂(1), which fully characterize the form factors for the B⁰→D^*-ℓ⁺ν_ℓ decay in the framework of heavy-quark effective field theory. The results, based on a selected sample of about 52 800 B⁰→D^*-ℓ⁺ν_ℓ decays, recorded by the BABAR detector, are ρ²=1.157±0.094±0.027, R₁(1)=1.327±0.131±0.043, R₂(1)=0.859±0.077±0.021, and F(1)|V_cb|=(34.7±0.4±1.0)×10^-3. The first error is the statistical and the second is the systematic uncertainty. Combining these measurements with the previous BABAR measurement of the form factors, which employs a different fit technique on a partial sample of the data, we improve the statistical precision of the result, ρ²=1.191±0.048±0.028, R₁(1)=1.429±0.061±0.044, R₂(1)=0.827±0.038±0.022, and F(1)|V_cb|=(34.4±0.3±1.1)×10^-3. Using lattice calculations for the axial form factor F(1), we extract |V_cb|=(37.4±0.3±1.2±_1.4^1.2)×10^-3, where the third error is due to the uncertainty in F(1). We also present a measurement of the exclusive branching fraction, B=(4.69±0.04±0.34)%.

We measure the absolute branching fraction for D⁰→K^-π⁺ using partial reconstruction of B̅ ⁰→D^*+Xℓ^-ν̅ _ℓ decays, in which only the charged lepton and the pion from the decay D^*+→D⁰π⁺ are used. Based on a data sample of 230×10⁶ BB̅ pairs collected at the Υ(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D⁰→K^-π⁺)=(4.007±0.037±0.072)%, where the first uncertainty is statistical and the second is systematic.

Using a data sample corresponding to an integrated luminosity of 342  fb^-1 collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a center-of-mass energy near 10.58 GeV, we measure B(τ^-→π^-π^-π⁺ν_τ(ex.K_S⁰))=(8.83±0.01±0.13)%, B(τ^-→K^-π^-π⁺ν_τ(ex.K_S⁰))=(0.273±0.002±0.009)%, B(τ^-→K^-π^-K⁺ν_τ)=(0.1346±0.0010±0.0036)%, and B(τ^-→K^-K^-K⁺ν_τ)=(1.58±0.13±0.12)×10^-5, where the uncertainties are statistical and systematic, respectively. These include significant improvements over previous measurements and a first measurement of B(τ^-→K^-K^-K⁺ν_τ) in which no resonance structure is assumed. We also report a first measurement of B(τ^-→ϕπ^-ν_τ)=(3.42±0.55±0.25)×10^-5, a new measurement of B(τ^-→ϕK^-ν_τ)=(3.39±0.20±0.28)×10^-5 and a first upper limit on B(τ^-→K^-K^-K⁺ν_τ(ex.ϕ)).

We report the results of a CP violation analysis of the decay B^±→D_{π⁺π^-π⁰}K^±, where D_{π⁺π^-π⁰} indicates a neutral D meson detected in the final state π⁺π^-π⁰, excluding K_S⁰π⁰. The analysis makes use of 324×10⁶ e⁺e^-→BB̅ events recorded by the BABAR experiment at the PEP-II e⁺e^- storage ring. Analyzing the π⁺π^-π⁰ Dalitz plot distribution and the B^±→D_{π⁺π^-π⁰}K^± branching fraction and decay rate asymmetry, we find the following one-standard-deviation constraints on the amplitude ratio and on the weak and strong phases: 0.06<r_B<0.78, -30°<γ<76°, -27°<δ<78°. We also measure the magnitudes and phases of the components of the D⁰→π⁺π^-π⁰ decay amplitude.

We present measurements of the time-dependent CP-violating asymmetries in B⁰→K_S⁰K_S⁰K_S⁰ decays based on 384×10⁶ Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We obtain the CP asymmetry parameters C=0.02±0.21±0.05 and S=-0.71±0.24±0.04, where the first uncertainties are statistical and the second systematic. These results are consistent with standard model expectations.

We report on a search for the process B⁺→K̅ ^*0(892)K⁺ using 232×10⁶ Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. From a signal yield of 25±13[stat]±7[syst] B⁺→K̅ ^*0(892)(→K^-π⁺)K⁺ events, we place an upper limit on the branching fraction B(B⁺→K̅ ^*0(892)K⁺) of 1.1×10^-6, at the 90% confidence level.

We present updated measurements of time-dependent CP asymmetries in fully-reconstructed neutral B decays to several CP eigenstates containing a charmonium meson. The measurements use a data sample of (383±4)×10⁶ Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II B factory. We determine sin⁡2β=0.714±0.032(stat)±0.018(syst) and |λ|=0.952±0.022(stat)±0.017(syst).

We present a measurement of the time-dependent CP asymmetry for the neutral B-meson decay into the CP=+1 final state K_S⁰π⁰π⁰, with K_S⁰→π⁺π^-. We use a sample of approximately 227 million B-meson pairs recorded at the Υ(4S) resonance with the BABAR detector at the PEP-II B-Factory at SLAC. From an unbinned maximum likelihood fit, we extract the mixing-induced CP-violation parameter S=0.72±0.71±0.08 and the direct CP-violation parameter C=0.23±0.52±0.13, where the first uncertainty is statistical and the second systematic.

We present results from an analysis of B⁰→ρ⁺ρ^- decays using (383.6±4.2)×10⁶ BB̅ pairs collected by the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The measurements of the B⁰→ρ⁺ρ^- branching fraction, longitudinal polarization fraction f_L, and the CP-violating parameters S_long and C_long are as follows: B(B⁰→ρ⁺ρ^-)=(25.5±2.1(stat)_-3.9^+3.6(syst))×10^-6, f_L=0.992±0.024(stat)_-0.013^+0.026(syst), S_long=-0.17±0.20(stat)_-0.06^+0.05(syst), C_long=0.01±0.15(stat)±0.06(syst). We determine the unitarity triangle angle α, using an isospin analysis of B→ρρ decays. One of the two solutions, α=[73.1,117.0]° at 68% confidence level, is compatible with standard model-based fits of existing data. Constraints on the unitarity triangle are also evaluated using an SU(3) symmetry-based approach.

The shape of the hadronic form factor f₊(q²) in the decay D⁰→K^-e⁺ν_e has been measured in a model independent analysis and compared with theoretical calculations. We use 75  fb^-1 of data recorded by the BABAR detector at the PEP-II electron-positron collider. The corresponding decay branching fraction, relative to the decay D⁰→K^-π⁺, has also been measured to be R_D=B(D⁰→K^-e⁺ν_e(γ))/B(D⁰→K^-π⁺(γ))=0.927±0.007±0.012. From these results, and using the present world average value for B(D⁰→K^-π⁺), the normalization of the form factor at q²=0 is determined to be f₊(0)=0.727±0.007±0.005±0.007 where the uncertainties are statistical, systematic, and from external inputs, respectively.

Motivated by the polarization anomaly in the B→ϕ(1020)K^*(892) decay, we extend our search for other K^* final states in the decay B⁰→ϕ(1020)K^*0 with the K^*0→K⁺π^- invariant mass above 1.6 GeV. The final states considered include the K^*(1680)⁰, K₃^*(1780)⁰, K₄^*(2045)⁰, and a Kπ spin-zero nonresonant component. We also search for B⁰→ϕD̅ ⁰ decay with the same final state. The analysis is based on a sample of about 384×10⁶ BB̅ pairs recorded with the BABAR detector. We place upper limits on the branching fractions B(B⁰→ϕK^*(1680)⁰)<3.5×10^-6, B(B⁰→ϕK₃^*(1780)⁰)<2.7×10^-6, B(B⁰→ϕK₄^*(2045)⁰)<15.3×10^-6, and B(B⁰→ϕD̅ ⁰)<11.7×10^-6 at 90% C.L. The nonresonant contribution is consistent with the measurements in the lower invariant mass range.

We determine the relative branching fractions of semileptonic B decays to charmed final states. The measurement is performed on the recoil from a fully reconstructed B meson in a sample of 362×10⁶ BB̅ pairs collected at the Υ(4S) resonance with the BABAR detector. A simultaneous fit to a set of discriminating variables is performed on a sample of B̅ →DXℓ^-ν̅ _ℓ decays to determine the contributions from the different channels. We measure Γ(B^-→Dℓ^-ν̅ _ℓ)/Γ(B^-→DXℓ^-ν̅ _ℓ)=0.227±0.014±0.016, Γ(B^-→D^*ℓ^-ν̅ _ℓ)/Γ(B^-→DXℓ^-ν̅ _ℓ)=0.582±0.018±0.030, and Γ(B^-→D^**ℓ^-ν̅ _ℓ)/Γ(B^-→DXℓ^-ν̅ _ℓ)=0.191±0.013±0.019 for the charged B sample, and Γ(B⁰̅ →Dℓ^-ν̅ _ℓ)/Γ(B⁰̅ →DXℓ^-ν̅ _ℓ)=0.215±0.016±0.013, Γ(B⁰̅ →D^*ℓ^-ν̅ _ℓ)/Γ(B⁰̅ →DXℓ^-ν̅ _ℓ)=0.537±0.031±0.036, and Γ(B⁰̅ →D^**ℓ^-ν̅ _ℓ)/Γ(B⁰̅ →DXℓ^-ν̅ _ℓ)=0.248±0.032±0.030 for the neutral B sample, where uncertainties are statistical and systematic, respectively.

We report a measurement of the time-dependent CP-asymmetry parameters S and C in color-suppressed B⁰→D^(*)0h⁰ decays, where h⁰ is a π⁰, η, or ω meson, and the decays to one of the CP eigenstates K⁺K^-, K_S⁰π⁰, or K_S⁰ω. The data sample consists of 383×10⁶  Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The results are S=-0.56±0.23±0.05 and C=-0.23±0.16±0.04, where the first error is statistical and the second is systematic.

We perform the first three-dimensional measurement of the amplitudes of B→ψ(2S)K^* and B→χ_c1K^* decays and update our previous measurement for B→J/ψK^*. We use a data sample collected with the BABAR detector at the PEP-II storage ring, corresponding to 232×10⁶ BB̅ pairs. The longitudinal polarization of decays involving a J^PC=1⁺⁺ χ_c1 meson is found to be larger than that with a 1^-- J/ψ or ψ(2S) meson. No direct CP-violating charge asymmetry is observed.

We study the decays B⁰→J/ψπ⁺π^- and B⁺→J/ψπ⁺π⁰, including intermediate resonances, using a sample of 382×10⁶ BB̅ pairs recorded by the BABAR detector at the PEP-II e⁺e^- B factory. We measure the branching fractions B(B⁰→J/ψρ⁰)=(2.7±0.3±0.2)×10^-5 and B(B⁺→J/ψρ⁺)=(5.0±0.7±0.3)×10^-5. We also set the following upper limits at the 90% confidence level: B(B⁰→J/ψπ⁺π^- nonresonant)<1.2×10^-5, B(B⁰→J/ψf₂)<4.6×10^-6, and B(B⁺→J/ψπ⁺π⁰ nonresonant)<7.3×10^-6. We measure the charge asymmetry in charged B decays to J/ψρ to be -0.11±0.12±0.08.

We present an analysis of inclusive Ω_c⁰ baryon production and decays in 230.5  fb^-1 of data recorded with the BABAR detector. Ω_c⁰ baryons are reconstructed in four final states (Ω^-π⁺, Ω^-π⁺π⁰, Ω^-π⁺π⁺π^-, Ξ^-K^-π⁺π⁺) and the corresponding ratios of branching fractions are measured. We also measure the momentum spectrum in the e⁺e^- center-of-mass frame. From the spectrum, we observe Ω_c⁰ production from B decays and in cc̅ events, and extract the two rates of production.

We have searched for D⁰-D̅ ⁰ mixing in D^*+→π⁺D⁰ decays with D⁰→K^(*)eν in a sample of e⁺e^-→cc̅ events produced near 10.58 GeV. The charge of the slow pion from charged D^* decay tags the charm flavor at production, and it is required to be consistent with the flavor of a fully reconstructed second charm decay in the same event. We observe 3 mixed candidates compared to 2.85 background events expected from simulation. We ascribe a 50% systematic uncertainty to this expected background rate. We find a central value for the mixing rate of 0.4×10^-4. Using a frequentist method, we set corresponding 68% and 90% confidence intervals at (-5.6,7.4)×10^-4 and (-13,12)×10^-4, respectively.

We study the processes e⁺e^-→K⁺K^-π⁺π^-γ, K⁺K^-π⁰π⁰γ and K⁺K^-K⁺K^-γ, where the photon is radiated from the initial state. About 34 600, 4400 and 2300 fully reconstructed events, respectively, are selected from 232  fb^-1 of BABAR data. The invariant mass of the hadronic final state defines the effective e⁺e^- center-of-mass energy, so that the K⁺K^-π⁺π^-γ data can be compared with direct measurements of the e⁺e^-→K⁺K^-π⁺π^- reaction; no direct measurements exist for the e⁺e^-→K⁺K^-π⁰π⁰ or e⁺e^-→K⁺K^-K⁺K^- reactions. Studying the structure of these events, we find contributions from a number of intermediate states, and we extract their cross sections where possible. In particular, we isolate the contribution from e⁺e^-→ϕ(1020)f₀(980) and study its structure near threshold. In the charmonium region, we observe the J/ψ in all three final states and several intermediate states, as well as the ψ(2S) in some modes, and measure the corresponding branching fractions. We see no signal for the Y(4260) and obtain an upper limit of B_{Y(4260)→ϕπ⁺π^-}·Γ_ee^Y<0.4  eV at 90% C.L.

We have performed a search for the flavor-changing neutral-current decays B→πℓ⁺ℓ^-, where ℓ⁺ℓ^- is either e⁺e^- or μ⁺μ^-, using a sample of 230×10⁶ Υ(4S)→BB̅ decays collected with the BABAR detector. We observe no evidence of a signal and measure the upper limit on the isospin-averaged branching fraction to be B(B→πℓ⁺ℓ^-)<9.1×10^-8 at 90% confidence level. We also search for the lepton-flavor-violating decays B→πe^±μ^∓ and measure an upper limit on the isospin-averaged branching fraction of B(B→πe^±μ^∓)<9.2×10^-8 at 90% confidence level.

We report a measurement of CP-violating asymmetries in B⁰→(ρπ)⁰→π⁺π^-π⁰ decays using a time-dependent Dalitz plot analysis. The results are obtained from a data sample of 375×10⁶ Υ(4S)→BB̅ decays, collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We measure 26 coefficients of the bilinear form-factor terms occurring in the time-dependent decay rate of the B⁰ meson. We derive the physically relevant quantities from these coefficients. In particular, we measure a constraint on the angle α of the unitarity triangle.

We report observations of CP violation in the decays B⁰→K⁺π^- and B⁰→π⁺π^- in a sample of 383×10⁶ Υ(4S)→BB̅ events. We find 4372±82 B⁰→K⁺π^- decays and measure the direct CP-violating charge asymmetry A_Kπ=-0.107±0.018(stat)_-0.004^+0.007(syst), which excludes the CP-conserving hypothesis with a significance of 5.5 standard deviations. In the same sample, we find 1139±49 B⁰→π⁺π^- decays and measure the CP-violating asymmetries S_ππ=-0.60±0.11(stat)±0.03(syst) and C_ππ=-0.21±0.09(stat)±0.02(syst). CP conservation in B⁰→π⁺π^- (S_ππ=C_ππ=0) is excluded at a confidence level 1-C.L.=8×10^-8, corresponding to 5.4 standard deviations.

We present the first observation of the decay B⁺→ρ⁺K⁰, using a data sample of 348  fb^-1 collected at the Υ(4S) resonance with the BABAR detector. The branching fraction and charge asymmetry are measured to be (8.0_-1.3^+1.4±0.6)×10^-6 and (-12.2±16.6±2.0)%, respectively, where the first uncertainty is statistical and the second is systematic. The charge asymmetry is defined by A_ch=(Γ_B^--Γ_B⁺)/(Γ_B^-+Γ_B⁺) with Γ_B^± the B^± decay rate. The significance of the observed branching fraction, including systematic uncertainties, is 7.9 standard deviations.

Using 385  fb^-1 of e⁺e^- collisions, we study the amplitudes of the singly Cabibbo-suppressed decay D⁰→K^-K⁺π⁰. We measure the strong phase difference between the D̅ ⁰ and D⁰ decays to K^*(892)⁺K^- to be -35.5°±1.9°(stat)±2.2°(syst), and their amplitude ratio to be 0.599±0.013(stat)±0.011(syst). We observe contributions from the Kπ and K^-K⁺ scalar and vector amplitudes, and analyze their angular moments. We find no evidence for charged κ, nor for higher spin states. We also perform a partial-wave analysis of the K^-K⁺ system in a limited mass range.