Study of CP Asymmetry in B0−¯B0 Mixing with Inclusive Dilepton Events

We present a measurement of the asymmetry A C P between same-sign inclusive dilepton samples ℓ + ℓ + and ℓ − ℓ − ( ℓ = e , μ ) from semileptonic B decays in Υ ( 4 S ) → B ¯ B events, using the complete data set recorded by the BABAR experiment near the Υ ( 4 S ) resonance, corresponding to 471 × 1 0 6 B ¯ B pairs. The asymmetry A C P allows comparison between the mixing probabilities P ( ¯ B 0 → B 0 ) and P ( B 0 → ¯ B 0 ) , and therefore probes C P and T violation. The result, A C P = [ − 3.9 ± 3.5 ( stat ) ± 1.9 ( syst ) ] × 1 0 − 3 , is consistent with the standard model expectation

Measurement of the e+e− → p¯p cross section in the energy range from 3.0 to 6.5 GeV

The e + e − → p ¯ p cross section and the proton magnetic form factor have been measured in the center-of-mass energy range from 3.0 to 6.5 GeV using the initial-state radiation technique with an undetected photon. This is the first measurement of the form factor at energies higher than 4.5 GeV. The analysis is based on 469     fb − 1 of integrated luminosity collected with the BABAR detector at the PEP-II collider at e + e − center-of-mass energies near 10.6 GeV. The branching fractions for the decays J / ψ → p ¯ p and ψ ( 2 S ) → p ¯ p have also been measured

Measurement of the B− → D0K*− branching fraction

From a sample of 232 × 10 6 Υ ( 4 S ) → B ¯¯¯ B events collected with the BABAR detector at the PEP-II B Factory in 1999-2004, we measure the B − → D 0 K * − ( 892 ) decay branching fraction using events where the K * − is reconstructed in the K 0 S π − mode and the D 0 in the K − π + , K − π + π 0 , and K − π + π + π − channels: B ( B − → D 0 K * − ( 892 ) ) = ( 5.29 ± 0.30 ( stat ) ± 0.34 ( syst ) ) × 10 − 4

Improved measurements of the branching fractions for B0 → π+π− and B0 → K+π−, and a search for B0 → K+K−

We present measurements of the branching fractions for the charmless two-body decays B 0 → π + π − and B 0 → K + π − , and a search for the decay B 0 → K + K − . We include the effects of final-state radiation from the daughter mesons for the first time, and quote branching fractions for the inclusive processes B 0 → h + h ' − n γ , where h and h ′ are pions or kaons. The maximum value of the sum of the energies of the n undetected photons, E max  γ , is mode-dependent. Using a data sample of approximately 227 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II asymmetric-energy e + e − collider at SLAC, we measure: B ( B 0 → π + π − n γ ; E max  γ = 150     MeV ) = ( 5.1 ± 0.4 ± 0.2 ) × 10 − 6 , B ( B 0 → K + π − n γ ; E max  γ = 105     MeV ) = ( 18.1 ± 0.6 ± 0.6 ) × 10 − 6 , B ( B 0 → K + K − n γ ; E max  γ = 59     MeV ) < 0.5 × 10 − 6 ( 90 %     confidence level ) , where the first uncertainty is statistical and the second is systematic. Theoretical calculations can be used to extrapolate from the above measurements the nonradiative branching fractions, B 0 . Using one such calculation, we find: B 0 ( B 0 → π + π − ) = ( 5.5 ± 0.4 ± 0.3 ) × 10 − 6 , B 0 ( B 0 → K + π − ) = ( 19.1 ± 0.6 ± 0.6 ) × 10 − 6 , B 0 ( B 0 → K + K − ) < 0.5 × 10 − 6 ( 90 %     confidence level ) . Meaningful comparison between theory and experiment, as well as combination of measurements from different experiments, can be performed only in terms of these nonradiative quantities

Measurement of time-dependent CP asymmetries in B0 → D(*)±π∓ and B0 → D±ρ∓ decays

We present updated results on time-dependent C P asymmetries in fully reconstructed B 0 → D ( * ) ± π ∓ and B 0 → D ± ρ ∓ decays in approximately 232 × 10 6 Υ ( 4 S ) → B ¯¯¯ B 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 C P violation angle 2 β + γ : a D π = − 0.010 ± 0.023 ± 0.007 , c D π lep = − 0.033 ± 0.042 ± 0.012 , a D ∗ π = − 0.040 ± 0.023 ± 0.010 , c D ∗ π lep = 0.049 ± 0.042 ± 0.015 , a D ρ = − 0.024 ± 0.031 ± 0.009 , c D ρ lep = − 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  ( 2 β + γ ) | > 0.64     ( 0.40 ) at 68% (90%) confidence level

Search for the decay B0 → K0SK0SK0L

We present the first search for the decay B 0 → K 0 S K 0 S K 0 L using a data sample of 232 × 10 6 B ¯¯¯ B pairs. We find no statistically significant evidence for the nonresonant component of this decay. Our central value for the branching fraction, assuming the true Dalitz distribution is uniform and excluding the ϕ resonance, is B ( B 0 → K 0 S K 0 S K 0 L ) = ( 2.4 + 2.7 − 2.5 ± 0.6 ) × 10 − 6 where the errors are statistical and systematic, respectively. We set a single-sided Bayesian upper limit of B ( B 0 → K 0 S K 0 S K 0 L ) < 7.4 × 10 − 6 at 90% confidence level using a uniform prior probability for physical values. Assuming the worst-case true Dalitz distribution, where the signal is entirely in the region of lowest efficiency, the 90% confidence level upper limit is B ( B 0 → K 0 S K 0 S K 0 L ) < 16 × 10 − 6

Evidence for the baryonic decay ¯B0 → D0Λ¯Λ

Evidence is presented for the baryonic B meson decay ¯ B 0 → D 0 Λ ¯ Λ based on a data sample of 471 × 10 6 B ¯ B pairs collected with the BABAR detector at the PEP-II asymmetric e + e − collider located at the SLAC National Accelerator Laboratory. The branching fraction is determined to be B ( ¯ B 0 → D 0 Λ ¯ Λ ) = ( 9.8 + 2.9 − 2.6 ± 1.9 ) × 10 − 6 , corresponding to a significance of 3.4 standard deviations including additive systematic uncertainties. A search for the related baryonic B meson decay ¯ B 0 → D 0 Σ 0 ¯ Λ with Σ 0 → Λ γ is performed and an upper limit B ( ¯ B 0 → D 0 Σ 0 ¯ Λ + ¯ B 0 → D 0 Λ ¯ Σ 0 ) < 3.1 × 10 − 5 is determined at 90% confidence level

Branching fraction measurement of ¯B0 → D(*)+π− and B− → D(*)0π−and isospin analysis of ¯B → D(*)π decays

Using 65 × 10 6 Υ ( 4 S ) → B ¯¯¯ B events collected with the BABAR detector at the PEP-II e + e − storage ring at the Stanford Linear Accelerator Center, we measure the color-favored branching fractions B ( ¯¯¯ B 0 → D + π − ) = ( 2.55 ± 0.05 ± 0.16 ) × 10 − 3 , B ( ¯¯¯ B 0 → D * + π − ) = ( 2.79 ± 0.08 ± 0.17 ) × 10 − 3 , B ( B − → D 0 π − ) = ( 4.90 ± 0.07 ± 0.22 ) × 10 − 3 and B ( B − → D * 0 π − ) = ( 5.52 ± 0.17 ± 0.42 ) × 10 − 3 , where the first error is statistical and the second is systematic. With these results and the current world average for the branching fraction for the color-suppressed decay ¯¯¯ B 0 → D ( * ) 0 π 0 , the cosines of the strong phase difference δ between the I = 1 / 2 and I = 3 / 2 isospin amplitudes are determined to be cos  δ = 0.872 + 0.008 + 0.031 − 0.007 − 0.029 for the ¯¯¯ B → D π process and cos  δ = 0.924 + 0.019 + 0.063 − 0.017 − 0.054 for the ¯¯¯ B → D ∗ π process. Under the isospin symmetry, the results for cos  δ suggest the presence of final-state interactions in the D π system

Search for the decay B0 → a±1ρ∓

We present a search for the rare B -meson decay B 0 → a ± 1 ρ ∓ with a ± 1 → π + π − π ± . We use ( 110 ± 1.2 ) × 10 6     Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We obtain an upper limit of 30 × 10 − 6     ( 90 % C . L . ) for the branching fraction product B ( B 0 → a ± 1 ρ ∓ ) B ( a ± 1 → π + π − π ± ) , where we assume that the a ± 1 decays exclusively to ρ 0 π ±

Search for a Dark Leptophilic Scalar in e(+) e(-) Collisions

Many scenarios of physics beyond the standard model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an e+e− collider, such a leptophilic scalar (ϕL) would be produced predominantly through radiation from a τ lepton. We report herein a search for e+e−→τ+τ−ϕL, ϕL→ℓ+ℓ− (ℓ=e, μ) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the ϕL coupling to leptons in the range 0.04<mϕL<7.0  GeV. These bounds significantly improve upon the current constraints, excluding almost entirely the parameter space favored by the observed discrepancy in the muon anomalous magnetic moment below 4 GeV at 90% confidence level