Search results

1,466 records were found.

We report the determination of the Cabibbo-Kobayashi-Maskawa CP-violating angle gamma through the combination of various measurements involving B^{+-} --> D K^{+-}, B^{+-} --> D^{*} K^{+-}, and B^{+-} --> D K^{*+-} decays performed by the BaBar experiment at the PEP-II e^{+}e^{-} collider at SLAC National Accelerator Laboratory. Using up to 474 million B\bar{B} pairs, we obtain gamma = (69 ^{+17}_{-16})^\circ (modulo 180^\circ). The total uncertainty is dominated by the statistical component, with the experimental and amplitude-model systematic uncertainties amounting to +-4^\circ. The corresponding two-standard-deviation region is 41^\circ < gamma < 102^\circ. This result is inconsistent with gamma = 0 with a significance of 5.9 standard deviations.
The process e+e- --> p anti-p gamma is studied using 469 fb-1 of integrated luminosity collected with the BABAR detector at the PEP-II collider, at an e+e- center-of-mass energy of 10.6 GeV. From the analysis of the p anti-p invariant mass spectrum, the energy dependence of the cross section for e+e- --> p anti-p is measured from threshold to 4.5 GeV. The energy dependence of the ratio of electric and magnetic form factors, |G_E/G_M|, and the asymmetry in the proton angular distribution are measured for p anti-p masses below 3 GeV. We also measure the branching fractions for the decays J/psi --> p anti-p and psi(2S) --> p anti p.
We report the measurement of the baryonic B decay B- -> SigmaC++ p- pi- pi-. Using a data sample of 467*10^6 B B-bar pairs collected with the BaBar detector at the PEP-II storage ring at SLAC, the measured branching fraction is (2.98 +/- 0.16 (stat) +/- 0.15 (syst) +/- 0.77 (LambdaC+))*10^{-4}, where the last error is due to the uncertainty in the branching fraction of the decay LambdaC+ -> p+ K- pi+. The data suggest the existence of resonant subchannels B- -> LambdaC(2595)+ p- pi- and, possibly, B- -> SigmaC++ anti-Delta-- pi-. We see unexplained structures in m(SigmaC++ pi- pi-) at 3.25 GeV/c^2, 3.8 GeV/c^2, and 4.2 GeV/c^2.
Based on the full BaBar data sample, we report improved measurements of the ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or mu. 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 2.0 sigma and 2.7 sigma, respectively. Taken together, our results disagree with these expectations at the 3.4 sigma level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model. Kinematic distributions presented here exclude large portions of the more general type III two-Higgs-doublet model, but there are solutions within this model compatible with the results.
Dark sectors charged under a new Abelian force have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A'), connecting the dark sector to the Standard Model. We present a search for a dark photon in the reaction e+e- -> gamma A', A'-> e+e-, mu+mu- using 514 fb-1 of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 10^-4 - 10^-3 for dark photon masses in the range 0.02 - 10.2 GeV. We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon.
We study the rare B meson decays B{+-,0} --> J/\psi\ K^+ K^- K{+-,0}, B{+-,0} --> J/\psi\ \phi\ K{+-,0}, and search for B0 --> J/\psi\ \phi, using 469 million BBbar events collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II e+e- asymmetric-energy collider. We present new measurements of branching fractions and a study of the J/\psi\phi mass distribution in search of new charmonium-like states. In addition, we search for the decay B0 --> J/\psi\ \phi, and find no evidence of a signal.
We present a measurement of D0-D0bar mixing and CP violation using the ratio of lifetimes simultaneously extracted from a sample of D0 mesons produced through the flavor-tagged process D*+ -> D0 pi+, where D0 decays to K-+pi+-, K-K+, or pi-pi+, along with the untagged decays D0 -> K-+pi+- and D0 -> K-K+. The lifetimes of the CP-even, Cabibbo-suppressed modes K-K+ and pi-pi+ are compared to that of the CP-mixed mode K-+pi+- in order to measure yCP and DeltaY. We obtain yCP = [0.72 +- 0.18 (stat) +- 0.12 (syst)]% and DeltaY = [0.09 +- 0.26 (stat) +- 0.06 (syst)]%, where DeltaY constrains possible CP violation. The yCP result excludes the null mixing hypothesis at 3.3 sigma significance. This analysis is based on an integrated luminosity of 468 fb-1 collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider.
We present measurements of the branching fractions of 3-prong and 5-prong tau decay modes using a sample of 430 million tau lepton pairs, corresponding to an integrated luminosity of 468 fb-1, collected with the BaBar detector at the PEP-II asymmetric energy e+e- storage rings. The \tau- --> (3\pi)- \eta \nu, \tau- --> (3\pi)- \omega \nu, and \tau- --> \pi- f_1(1285)\nu, branching fractions are presented as well as a new limit on the branching fraction of the isospin-forbidden, second-class current, \tau- --> \pi-\eta'(958)\nu, decay. We find no evidence for charged kaons in these decay modes and place the first upper limits on their branching fractions.
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})...
In a sample of 471 million BB events collected with the BABAR detector at the PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is either e+e- or mu+mu-. We report results on partial branching fractions and isospin asymmetries in seven bins of di-lepton mass-squared. We further present CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi resonance. We find no evidence for CP or lepton-flavor violation. The partial branching fractions and isospin asymmetries are consistent with the Standard Model predictions and with results from other experiments.
Want to know more?If you want to know more about this cutting edge product, or schedule a demonstration on your own organisation, please feel free to contact us or read the available documentation at http://www.keep.pt/produtos/retrievo/?lang=en