Based on the full BABAR data sample, we report improved measurements of the ratios R(D(*))=B(B̄→D(*)τ⁻ν¯τ)/B(B̄→D(*)ll¯ν¯l), where l is either e or μ. These ratios are sensitive to new physics ...contributions in the form of a charged Higgs boson. We measure R(D)=0.440±0.058±0.042 and R(D*)=0.332±0.024±0.018, which exceed the standard model expectations by 2.0σ and 2.7σ, respectively. Taken together, our results disagree with these expectations at the 3.4σ level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.
A precise measurement of the cross section of the process $e^+e^-\to\pi^+\pi^-(\gamma)$ from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using $232\invfb$ ...of data collected with the BaBar detector at $e^+e^-$ center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process $e^+e^-\to\mu^+\mu^-(\gamma)\gamma_{\rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e^+e^-\to\pi^+\pi^-(\gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $\rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $\pi\pi$ cross section from threshold to 1.8GeV is $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.
Evidence of B + → τ + ν decays with hadronic B tags Grauges, E.; Palano, A.; Eigen, G. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2013, Letnik:
88, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a search for the decay B + → τ + ν using 467.8 × 10 6 B ¯¯¯ B pairs collected at the Υ ( 4 S ) resonance with the BABAR detector at the SLAC PEP-II B -Factory. We select a sample of events ...with one completely reconstructed B − in the hadronic decay mode ( B − → D ( * ) 0 X − and B − → J / ψ X − ). We examine the rest of the event to search for a B + → τ + ν decay. We identify the τ + lepton in the following modes: τ + → e + ν ¯ ν , τ + → μ + ν ¯ ν , τ + → π + ¯ ν and τ + → ρ + ¯ ν . We find an excess of events with respect to the expected background, which excludes the null signal hypothesis at the level of 3.8 σ (including systematic uncertainties) and corresponds to a branching fraction value of B ( B + → τ + ν ) = ( 1.83 + 0.53 − 0.49 ( stat ) ± 0.24 ( syst ) ) × 10 − 4 .
We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the Upsilon(4S), Upsilon(3S), and ...Upsilon(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e- --> e+e- and (for the Upsilon(4S) only) e+e- --> mu+mu- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross sections of e+e- --> e+e- and +e- --> mu+mu-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross sections. For data collected on the Upsilon(3S) and Upsilon(2S) resonances, an additional uncertainty arises due to Upsilon --> e+e- background. For data collected off the Upsilon resonances, we estimate an additional uncertainty due to the time-dependent efficiency variations, which can affect the short off-resonance runs.
PDF
