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.
Many models of physics beyond the standard model predict the existence of new Abelian forces with new gauge bosons mediating interactions between "dark sectors" and the standard model. We report a ...search for a dark boson Z' coupling only to the second and third generations of leptons in the reaction e super(+) e super(?)arrowrightmu super(+)mu super(?)Z',Z'arrowrightmu super(+) mu? using 514fb super(?1) of data collected by the BABAR experiment. No significant signal is observed for Z' masses in the range 0.212-10 GeV. Limits on the coupling parameter g' as low as 7x10 super(?4) are derived, leading to improvements in the bounds compared to those previously derived from neutrino experiments.
The process e+e−→π+π−2π0γ is investigated by means of the initial-state radiation technique, where a photon is emitted from the incoming electron or positron. Using 454.3 fb−1 of data collected ...around a center-of-mass energy of s=10.58 GeV by the BABAR experiment at SLAC, approximately 150000 signal events are obtained. The corresponding nonradiative cross section is measured with a relative uncertainty of 3.6% in the energy region around 1.5 GeV, surpassing all existing measurements in precision. Using this new result, the channel’s contribution to the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated as (gμπ+π−2π0−2)/2=(17.9±0.1stat±0.6syst)×10−10 in the energy range 0.85 GeV<ECM<1.8 GeV. In the same energy range, the impact on the running of the fine-structure constant at the Z0-pole is determined as Δαπ+π−2π0(MZ2)=(4.44±0.02stat±0.14syst)×10−4. Furthermore, intermediate resonances are studied and especially the cross section of the process e+e−→ωπ0→π+π−2π0 is measured.
We study the process e + e − → e + e − η ′ in the double-tag mode and measure for the first time the γ * γ * → η ′ transition form factor F η′ ( Q 2 1 , Q 2 2 ) in the momentum-transfer range 2 < Q 2 ...1 , Q 2 2 < 60 GeV 2 . The analysis is based on a data sample corresponding to an integrated luminosity of around 469 fb − 1 collected at the PEP-II e + e − collider with the BABAR detector at center-of-mass energies near 10.6 GeV.
The decay τ−→K−KSντ has been studied using 430×106 e+e−→τ+τ− events produced at a center-of-mass energy around 10.6 GeV at the PEP-II collider and studied with the BABAR detector. The mass spectrum ...of the K−KS system has been measured and the spectral function has been obtained. The measured branching fraction B(τ−→K−KSντ)=(0.739±0.011(stat)±0.020(syst))×10−3 is found to be in agreement with earlier measurements.
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