Search for the decay B^+ → τ^+ν_τ

We search for the rare leptonic decay B^+ → τ^+ν_τ in a sample of 232 × 10^6 BB̅ pairs collected with the BABAR detector at the SLAC PEP-II B-Factory. Signal events are selected by examining the properties of the B meson recoiling against the semileptonic decay B^- → D^9*0)ℓ^-ν̅_ ℓ. We find no evidence for a signal and set an upper limit on the branching fraction of B(B^+ → τ^+ν_τ)<2.8 × 10^9-4) at the 90% confidence level. We combine this result with a previous, statistically independent BABAR search for B+→τ+ντ to give an upper limit of B(B^+ → τ^+ν_τ)<2.6 × 10^(-4) at the 90% confidence level

Branching fraction limits for B^0 decays to η′η, η′π^0 and ηπ^0

We describe searches for decays to two-body charmless final states η′η, η′π^0 and ηπ^0 of B^0 mesons produced in e^+e^- annihilation. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 232 × 10^6 produced BB̅ pairs. The results for branching fractions are, in units of 10^(-6) (upper limits at 90% C.L.): B(B^0 → η′η)=0.2^(+0.7)_(-0.5) ± 0.4(<1.7), B(B^0 → ηπ^0) = 0.6^(+0.5)_(-0.4) ± 0.1(<1.3), and B(B^0 → η′π^0) = 0.8^(+0.8)_(-0.6) ± 0.1(<2.1). The first error quoted is statistical and the second systematic

Measurement of time-dependent CP asymmetries in B^0→D^((*)±)π^∓ and B^0→D^±ρ^∓ decays

We present updated results on time-dependent CP asymmetries in fully reconstructed B^0→D^((*)±)π^∓ and B^0→D^±ρ^∓ decays in approximately 232×10^6 Υ(4S)→BB events collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. From a time-dependent maximum-likelihood fit we obtain for the parameters related to the CP violation angle 2β+γ: a^(Dπ)=-0.010±0.023±0.007, c_(lep)^(Dπ)=-0.033±0.042±0.012, a^(D*π)=-0.040±0.023±0.010, c_(lep)D^(*π)=0.049± 0.042±0.015,a^(Dρ)=-0.024±0.031±0.009, c_(lep)^(Dρ)=-0.098±0.055±0.018, where the first error is statistical and the second is systematic. Using other measurements and theoretical assumptions, we interpret the results in terms of the angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle and find |sin⁡(2β+γ)|>0.64  (0.40) at 68% (90%) confidence level

The e^+e^- → 3(π^+π^-), 2(π^+π^-π^0) and K^+K^-2(π^+π^-) cross sections at center-of-mass energies from production threshold to 4.5 GeV measured with initial-state radiation

We study the processes e^+e^- → 3(π^+π^-)γ, 2(π^+π^-π^0)γ and K^+K^-2(π^+π^-)γ, with the photon radiated from the initial state. About 20 000, 33 000 and 4000 fully reconstructed events, respectively, have been 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 these data can be compared with the corresponding direct e^+e^- measurements. From the 3(π^+π^-), 2(π^+π^-π^0) and K^+K^-2(π^+π^-) mass spectra, the cross sections for the processes e^+e^- → 3(π^+π^-), e^+e^- → 2(π^+π^-π^0) and e^+e^- → K^+K^-2(π^+π^-) are measured for center-of-mass energies from production threshold to 4.5 GeV. The uncertainty in the cross section measurement is typically 6%–15%. We observe a structure at 1.9 GeV in both cross sections and a resonance structure with mass 1645 ± 0.008  GeV/c^2 and width 0.114 ± 0.014  GeV when the ω(782)η final state is extracted. We observe the J/ψ in all these final states and measure the corresponding branching fractions

Measurement of branching fractions and CP-violating charge asymmetries for B-meson decays to D^(*)D^(*), and implications for the Cabibbo-Kobayashi-Maskawa angle γ

We present measurements of the branching fractions and charge asymmetries of B decays to all D^(*)D^(*) modes. Using 232×10^6 BB pairs recorded on the Υ(4S) resonance by the BABAR detector at the e^+e^- asymmetric B factory PEP-II at the Stanford Linear Accelerator Center, we measure the branching fractions B(B^0→D^(*+)D^(*-))=(8.1±0.6±1.0)×10^(-4), B(B^0→D^(*±)D^∓)=(5.7±0.7±0.7)×10^(-4), B(B^0→D^+D^-)=(2.8±0.4±0.5)×10^(-4), B(B^+→D^(*+)D^(*0))=(8.1±1.2±1.2)×10^(-4), B(B^+→D^*+D^0)=(3.6±0.5±0.4)×10^(-4), B(B^+→D^+D^(*0))=(6.3±1.4±1.0)×10^(-4), and B(B^+→D^+D^(0))=(3.8±0.6±0.5)×10^(-4), where in each case the first uncertainty is statistical and the second systematic. We also determine the limits B(B^0→D^(*0)D^(*0))<0.9×10^(-4), B(B^0→D^(*0)D^0)<2.9×10^(-4), and B(B^0→D^0D^0)<0.6×10^(-4), each at 90% confidence level. All decays above denote either member of a charge-conjugate pair. We also determine the CP-violating charge asymmetries A(B^0→D^(*±)D^∓)=0.03±0.10±0.02, A(B^+→D^(*+)D^(*0))=-0.15±0.11±0.02, A(B^+→D^(*+)D^0)=-0.06±0.13±0.02, A(B^+→D^+D^(*0))=0.13±0.18±0.04, and A(B^+→D^+D^0)=-0.13±0.14±0.02. Additionally, when we combine these results with information from time-dependent CP asymmetries in B^0→D^((*)+)D^((*)-) decays and world-averaged branching fractions of B decays to D_s^(*)D^(*) modes, we find the Cabibbo-Kobayashi-Maskawa phase γ is favored to lie in the range (0.07–2.77) radians (with a +0 or +π radians ambiguity) at 68% confidence level

Search for the decay τ-→3π^-2π^+2π^0ν_τ

A search for the decay of the τ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider. The analysis uses 232  fb^(-1) of data at center-of-mass energies on or near the Υ(4S) resonance. We observe 10 events with an expected background of 6.5_(-1.4)^(+2.0) events. In the absence of a signal, we set the limit on the branching ratio B(τ-→3π^-2π^+2π^0ν_τ)<3.4×10^(-6) at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode τ-→2ωπ-ν_τ. We observe 1 event with an expected background of 0.4+1.0/-0.4 events and calculate the upper limit B(τ-→2ωπ-ν_τ)<5.4×10^(-7) at the 90% confidence level. This is the first upper limit for this mode

Search for the charmed pentaquark candidate Θ_c(3100)^0 in e^+e^- annihilations at √s=10.58 GeV

We search for the charmed pentaquark candidate reported by the H1 collaboration, the Θ_c(3100)^0, in e^+e^- interactions at a center-of-mass (c.m.) energy of 10.58 GeV, using 124  fb^(-1) of data recorded with the BABAR detector at the PEP-II e^+e^- facility at SLAC. We find no evidence for such a state in the same pD^(*-) decay mode reported by H1, and we set limits on its production cross section times branching fraction into pD^(*-) as a function of c.m. momentum. The corresponding limit on its total rate per e^+e^-→qq event, times branching fraction, is about 3 orders of magnitude lower than rates measured for the charmed Λ_c and Σ_c baryons in such events

Observation of B^0 Meson Decay to a_1^±(1260)π^∓

We present a measurement of the branching fraction of the decay B^0→a_1^±(1260)π^∓ with a_1^±(1260)→π^∓π^±π^±. The data sample corresponds to 218×10^6 BB pairs produced in e^+e^- annihilation through the Υ(4S) resonance. We measure the branching fraction B(B^0→a_1^±(1260)π^∓)B(a_1^±(1260)→π^∓π^±π^±)=(16.6±1.9±1.5)×10^(-6), where the first error quoted is statistical and the second is systematic

Measurements of branching fractions, rate asymmetries, and angular distributions in the rare decays B→Kℓ^+ℓ^- and B→K^*ℓ^+ℓ^-

We present measurements of the flavor-changing neutral current decays B→Kℓ^+ℓ^- and B→K^*ℓ^+ℓ^-, where ℓ^+ℓ^- is either an e^+e^- or μ^+μ^- pair. The data sample comprises 229×10^6  Υ(4S)→BB decays collected with the BABAR detector at the PEP-II e^+e^- storage ring. Flavor-changing neutral current decays are highly suppressed in the standard model and their predicted properties could be significantly modified by new physics at the electroweak scale. We measure the branching fractions B(B→Kℓ^+ℓ^-)=(0.34±0.07±0.02)×10^(-6), B(B→K^*ℓ^+ℓ^-)=(0.78-0.17^(+0.19)±0.11)×10^(-6), the direct CP asymmetries of these decays, and the relative abundances of decays to electrons and muons. For two regions in ℓ^+ℓ^- mass, above and below m_(J/ψ), we measure partial branching fractions and the forward-backward angular asymmetry of the lepton pair. In these same regions we also measure the K^* longitudinal polarization in B→K^*ℓ^+ℓ^- decays. Upper limits are obtained for the lepton-flavor-violating decays B→Keμ and B→K^*eμ. All measurements are consistent with standard model expectation

Study of the decay B^0→D^(*+)ωπ^-

We report on a study of the decay B^0→D^(*+)ωπ^- with the BABAR detector at the PEP-II B-factory at the Stanford Linear Accelerator Center. Based on a sample of 232×10^6 BB decays, we measure the branching fraction B(B^0→D^(*+)ωπ^-)=(2.88±0.21(stat.)±0.31(syst.))×10^(-3). We study the invariant mass spectrum of the ωπ^- system in this decay. This spectrum is in good agreement with expectations based on factorization and the measured spectrum in τ-→ωπ-ν_τ. We also measure the polarization of the D^(*+) as a function of the ωπ^- mass. In the mass region 1.1 to 1.9 GeV we measure the fraction of longitudinal polarization of the D^(*+) to be ΓL/Γ=0.654±0.042(stat.)±0.016(syst.). This is in agreement with the expectations from heavy-quark effective theory and factorization assuming that the decay proceeds as B^(-0)→D^(*+)ρ(1450)-, ρ(1450)^-→ωπ^-