Search Results (642 total)

We report a Dalitz-plot analysis of the charmless hadronic decays of charged B mesons to the final state K^±π^∓π^±. Using a sample of (383.2±4.2)×10⁶ BB̅ pairs collected by the BABAR detector, we measure CP-averaged branching fractions and direct CP asymmetries for intermediate resonant and nonresonant contributions. We find evidence for direct CP violation in the decay B^±→ρ⁰(770)K^±, with a CP-violation parameter A_CP=(+44±10±4_-13⁺⁵)%.

We present measurements of the branching fraction and time-dependent CP asymmetries in B⁰→J/ψπ⁰ decays based on 466×10⁶ Υ(4S)→BB̅ events collected with the BABAR detector at the SLAC PEP-II asymmetric-energy B factory. We measure the CP asymmetry parameters S=-1.23±0.21(stat)±0.04(syst) and C=-0.20±0.19(stat)±0.03(syst), where the measured value of (S, C) is 4.0 standard deviations from (0, 0) including systematic uncertainties. The branching fraction is determined to be B(B⁰→J/ψπ⁰)=[1.69±0.14(stat)±0.07(syst)]×10^-5.

We present a study of the decay B^-→D_(CP)⁰K^- and its charge conjugate, where D_(CP)⁰ is reconstructed in both a non-CP flavor eigenstate and in CP (CP-even and CP-odd) eigenstates, based on a sample of 382 million Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II e⁺e^- storage ring. We measure the direct CP asymmetries A_CP± and the ratios of the branching fractions R_CP±: A_CP+=0.27±0.09(stat)±0.04(syst), A_CP-=-0.09±0.09(stat)±0.02(syst), R_CP+=1.06±0.10(stat)±0.05(syst), R_CP-=1.03±0.10(stat)±0.05(syst). We also express the results in terms of the so-called Cartesian coordinates x₊, x_-, and r²: x₊=-0.09±0.05(stat)±0.02(syst), x_-=0.10±0.05(stat)±0.03(syst), r²=0.05±0.07(stat)±0.03(syst). These results will help to better constrain the phase parameter γ=arg⁡(-V_udV_ub^*/V_cdV_cb^*) of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

Using 226×10⁶ BB̅ events recorded on the Υ(4S) resonance with the BABAR detector at the SLAC e⁺e^- PEP-II storage rings, we reconstruct B^-→D^*0e^-ν̅ _e decays using the decay chain D^*0→D⁰π⁰ and D⁰→K^-π⁺. From the dependence of their differential rate on w, the dot product of the four velocities of B^- and D^*0, and using the form factor description by Caprini et al. with the parameters F(1) and ρ_A1², we obtain the results ρ_A1²=1.16±0.06±0.08, F(1)|V_cb|=(35.9±0.6±1.4)×10^-3, and B(B^-→D^*0e^-ν̅ _e)=(5.56±0.08±0.41)%.

The τ^-→ηπ^-π⁺π^-ν_τ decay with the η→γγ mode is studied using 384  fb^-1 of data collected by the BABAR detector. The branching fraction is measured to be (1.60±0.05±0.11)×10^-4. It is found that τ^-→f₁(1285)π^-ν_τ→ηπ^-π⁺π^-ν_τ is the dominant decay mode with a branching fraction of (1.11±0.06±0.05)×10^-4. The first error on the branching fractions is statistical and the second systematic. Note that no particle identification algorithm is applied to the charged tracks to distinguish pions from kaons. In addition, a 90% confidence level upper limit on the branching fraction of the τ^-→η^′(958)π^-ν_τ decay is measured to be 7.2×10^-6. This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.

We present measurements of the decays B⁺→X(3872)K⁺ and B⁰→X(3872)K⁰ with X(3872)→J/ψπ⁺π^-. The data sample used, collected with the BABAR detector at the PEP-II e⁺e^- asymmetric-energy storage ring, corresponds to 455×10⁶BB̅ pairs. Branching fraction measurements of B(B⁺→X(3872)K⁺)×B(X(3872)→J/ψπ⁺π^-)=(8.4±1.5±0.7)×10^-6 and B(B⁰→X(3872)K⁰)×B(X(3872)→J/ψπ⁺π^-)=(3.5±1.9±0.4)×10^-6 are obtained. We set an upper limit on the natural width of the X(3872) of Γ<3.3  MeV/c² at the 90% confidence level.

This paper reports measurements of processes: e⁺e^-→γK_S⁰K^±π^∓, e⁺e^-→γK⁺K^-π⁰, e⁺e^-→γϕη, and e⁺e^-→γϕπ⁰. The initial-state radiated photon allows to cover the hadronic final state in the energy range from thresholds up to ≈4.6  GeV. The overall size of the data sample analyzed is 232  fb^-1, collected by the BABAR detector running at the PEP-II e⁺e^- storage ring. From the Dalitz plot analysis of the K_S⁰K^±π^∓ final state, moduli, and relative phase of the isoscalar and the isovector components of the e⁺e^-→KK^*(892) cross section are determined. Parameters of ϕ and ρ recurrences are also measured, using a global fitting procedure which exploits the interconnection among amplitudes, moduli, and phases of the e⁺e^-→K_S⁰K^±π^∓, K⁺K^-π⁰, ϕη final states. The cross section for the OZI-forbidden process e⁺e^-→ϕπ⁰, and the J/ψ branching fractions to KK^*(892) and K⁺K^-η are also measured.

We present searches for the leptonic decays B⁺→ℓ⁺ν and the lepton flavor violating decays B⁰→ℓ^±τ^∓, where ℓ=e, μ, with data collected by the BABAR experiment at SLAC. This search demonstrates a novel technique in which we fully reconstruct the accompanying B̅ in Υ(4S)→BB̅ events, and look for a monoenergetic lepton from the signal B decay. The signal yield is extracted from a fit to the signal lepton candidate momentum distribution in the signal B rest frame. Using a data sample of approximately 378×10⁶ BB̅ pairs (342  fb^-1), we find no evidence of signal in any of the decay modes. Branching fraction upper limits of B(B⁺→e⁺ν)<5.2×10^-6, B(B⁺→μ⁺ν)<5.6×10^-6, B(B⁰→e⁺τ^-)<2.8×10^-5 and B(B⁰→μ⁺τ^-)<2.2×10^-5, are obtained at 90% confidence level.

We report on our search for decays proceeding via a tree-level b→c quark transition in which a gluon radiates into an ss̅ pair. We present observations of the decays B^-→D_s^(*)+K^-π^- and B̅ ⁰→D_s⁺K_S⁰π^- and evidence for B^-→D_s⁺K^-K^- and set upper limits on the branching fractions for B̅ ⁰→D_s^*+K_S⁰π^- and B^-→D_s^*+K^-K^- using 383×10⁶ Υ(4S)→BB̅ events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of D_s^(*)+K^- pairs from B^-→D_s^(*)+K^-π^- decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the D_s^(*)+K^- threshold.

We present partial branching fractions for inclusive charmless semileptonic B decays B̅ →X_uℓν̅ , and the determination of the Cabibbo-Kobayashi-Maskawa matrix element |V_ub|. The analysis is based on a sample of 383×10⁶ Υ(4S) decays into BB̅ pairs collected with the BABAR detector at the SLAC PEP-II e⁺e^- storage rings. We select events using the invariant mass M_X of the hadronic system, the invariant mass squared, q², of the lepton and neutrino pair, the kinematic variable P₊, or one of their combinations. We then determine partial branching fractions in limited regions of phase space: ΔB=(1.18±0.09_stat±0.07_syst±0.01_theor)×10^-3 (M_X<1.55  GeV/c²), ΔB=(0.95±0.10_stat±0.08_syst±0.01_theor)×10^-3 (P₊<0.66  GeV/c), and ΔB=(0.81±0.08_stat±0.07_syst±0.02_theor)×10^-3 (M_X<1.7  GeV/c², q²>8  GeV²/c⁴). Corresponding values of |V_ub| are extracted using several theoretical calculations.

We present for the first time a measurement of the weak phase 2β+γ obtained from a time-dependent Dalitz plot analysis of B⁰→D^∓K⁰π^± decays. Using a sample of approximately 347×10⁶ BB̅ pairs collected by the BABAR detector at the PEP-II asymmetric-energy storage rings and assuming the ratio r of the b→u and b→c decay amplitudes to be 0.3, we obtain 2β+γ=(83±53±20)° and the equivalent solution at +180°. The magnitudes and phases for the resonances associated with the b→c transitions are also extracted from the fit.

We report a measurement of the branching fractions for B̅ →D^(*)(π)ℓ^-ν̅ _ℓ decays based on 341.1  fb^-1 of data collected at the Υ(4S) resonance with the BABAR detector at the SLAC PEP-II e⁺e^- storage rings. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode. We obtain B(B^-→D⁰ℓ^-ν̅ _ℓ)=(2.33±0.09_stat±0.09_syst)%, B(B^-→D^*0ℓ^-ν̅ _ℓ)=(5.83±0.15_stat±0.30_syst)%, B(B̅ ⁰→D⁺ℓ^-ν̅ _ℓ)=(2.21±0.11_stat±0.12_syst)%, B(B̅ ⁰→D^*+ℓ^-ν̅ _ℓ)=(5.49±0.16_stat±0.25_syst)%, B(B^-→D⁺π^-ℓ^-ν̅ _ℓ)=(0.42±0.06_stat±0.03_syst)%, B(B^-→D^*+π^-ℓ^-ν̅ _ℓ)=(0.59±0.05_stat±0.04_syst)%, B(B̅ ⁰→D⁰π⁺ℓ^-ν̅ _ℓ)=(0.43±0.08_stat±0.03_syst)%, and B(B̅ ⁰→D^*0π⁺ℓ^-ν̅ _ℓ)=(0.48±0.08_stat±0.04_syst)%.

We report results of a search for CPT and Lorentz violation in B⁰-B̅ ⁰ oscillations using inclusive dilepton events from 232×10⁶ Υ(4S)→BB̅ decays recorded by the BABAR detector at the PEP-II B Factory at SLAC. We find 2.8σ significance, compatible with no signal, for variations in the complex CPT violation parameter z at the Earth’s sidereal frequency and extract values for the quantities Δa_μ in the general Lorentz-violating standard-model extension. The spectral powers for variations in z over the frequency range 0.26  yr^-1 to 2.1  solar day^-1 are also compatible with no signal.

We present a measurement of the branching fraction and photon-energy spectrum for the decay B→X_sγ using data from the BABAR experiment. The data sample corresponds to an integrated luminosity of 210  fb^-1, from which approximately 680 000 BB̅ events are tagged by a fully reconstructed hadronic decay of one of the B mesons. In the decay of the second B meson, an isolated high-energy photon is identified. We measure B(B→X_sγ)=(3.66±0.85_stat±0.60_syst)×10^-4 for photon energies E_γ above 1.9 GeV in the B rest frame. From the measured spectrum we calculate the first and second moments for different minimum photon energies, which are used to extract the heavy-quark parameters m_b and μ_π². In addition, measurements of the direct CP asymmetry and isospin asymmetry are presented.

We present a search for the decays B⁰→e⁺e^-, B⁰→μ⁺μ^-, and B⁰→e^±μ^∓ using data collected with the BABAR detector at the PEP-II e⁺e^- collider at SLAC. Using a data set corresponding to 384×10⁶ BB̅ pairs, we do not find evidence of any of the three decay modes. We obtain upper limit on the branching fractions, at 90% confidence level, of B(B⁰→e⁺e^-)<11.3×10^-8, B(B⁰→μ⁺μ^-)<5.2×10^-8, and B(B⁰→e^±μ^∓)<9.2×10^-8.

We report measurements of B-meson decays into two- and three-body final states containing two charmed baryons using a sample of 230×10⁶ Υ(4S)→BB̅ decays. We find significant signals in two modes, measuring branching fractions B(B^-→Λ_c⁺Λ̅ _c^-K^-)=(1.14±0.15±0.17±0.60)×10^-3 and B(B^-→Ξ_c⁰Λ̅ _c^-)×B(Ξ_c⁰→Ξ^-π⁺)=(2.08±0.65±0.29±0.54)×10^-5, where the uncertainties are statistical, systematic, and from the branching fraction B(Λ_c⁺→pK^-π⁺), respectively. We also set upper limits at the 90% confidence level on two other modes: B(B̅ ⁰→Ξ_c⁺Λ̅ _c^-)×B(Ξ_c⁺→Ξ^-π⁺π⁺)<5.6×10^-5 and B(B̅ ⁰→Λ_c⁺Λ̅ _c^-K̅ ⁰)<1.5×10^-3. We observe structure centered at an invariant mass of 2.93  GeV/c² in the Λ_c⁺K^- mass distribution of the decay B^-→Λ_c⁺Λ̅ _c^-K^-.

We report the observation of the b→d penguin-dominated decay B⁰→K^*0K̅ ^*0 with a sample of 383.2±4.2 million BB̅ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e⁺e^- collider at the Stanford Linear Accelerator Center. The measured branching fraction is B(B⁰→K^*0K̅ ^*0)=[1.28_-0.30^+0.35±0.11]×10^-6 and the fraction of longitudinal polarization is f_L(B⁰→K^*0K̅ ^*0)=0.80_-0.12^+0.10±0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for B(B⁰→K^*0K^*0)<0.41×10^-6.

A search for lepton flavor violating decays of a τ to a lighter-mass charged lepton and an ω vector meson is performed using 384.1  fb^-1 of e⁺e^- annihilation data collected with the BABAR detector at the Stanford Linear Accelerator Center PEP-II storage ring. No signal is found, and the upper limits on the branching ratios are determined to be B(τ^±→e^±ω)<1.1×10^-7 and B(τ^±→μ^±ω)<1.0×10^-7 at 90% confidence level.

We measure time-integrated CP-violating asymmetries of neutral charmed mesons in the modes D⁰→K^-K⁺ and D⁰→π^-π⁺ with the highest precision to date by using D⁰→K^-π⁺ decays to correct detector asymmetries. An analysis of 385.8  fb^-1 of data collected with the BABAR detector yields values of a_CP^KK=(0.00±0.34(stat)±0.13(syst))% and a_CP^ππ=(-0.24±0.52(stat)±0.22(syst))%, which agree with standard model predictions.

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 present branching fraction measurements of the decays B⁺→a₁⁺(1260)K⁰ and B⁰→a₁^-(1260)K⁺ with a₁^±(1260)→π^∓π^±π^±. The data sample corresponds to 383×10⁶ BB̅ pairs produced in e⁺e^- annihilation through the Υ(4S) resonance. We measure the products of the branching fractions B(B⁺→a₁⁺(1260)K⁰)B(a₁⁺(1260)→π^-π⁺π⁺)=(17.4±2.5±2.2)×10^-6 and B(B⁰→a₁^-(1260)K⁺)B(a₁^-(1260)→π⁺π^-π^-)=(8.2±1.5±1.2)×10^-6. We also measure the charge asymmetries A_ch(B⁺→a₁⁺(1260)K⁰)=0.12±0.11±0.02 and A_ch(B⁰→a₁^-(1260)K⁺)=-0.16±0.12±0.01. The first uncertainty quoted is statistical and the second is systematic.