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
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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 .
In a sample of 471 × 10 6 B ¯¯¯ B 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 μ + μ − . ...We report results on partial branching fractions and isospin asymmetries in seven bins of dilepton mass-squared. We further present C P and lepton-flavor asymmetries for dilepton masses below and above the J / ψ resonance. We find no evidence for C P or lepton-flavor violation. The partial branching fractions and isospin asymmetries are consistent with the Standard Model predictions and with results from other experiments.
We search for di-muon decays of a low-mass Higgs boson ( A 0 ) produced in radiative Υ ( 1 S ) decays. The Υ ( 1 S ) sample is selected by tagging the pion pair in the Υ ( 2 S , 3 S ) → π + π − Υ ( 1 ...S ) transitions, using a data sample of 92.8 × 10 6 Υ ( 2 S ) and 116.8 × 10 6 Υ ( 3 S ) events collected by the BABAR detector. We find no evidence for A 0 production and set 90% confidence level upper limits on the product branching fraction B ( Υ ( 1 S ) → γ A 0 ) × B ( A 0 → μ + μ − ) in the range of ( 0.28 − 9.7 ) × 10 − 6 for 0.212 ≤ m A 0 ≤ 9.20 GeV / c 2 . The results are combined with our previous measurements of Υ ( 2 S , 3 S ) → γ A 0 , A 0 → μ + μ − to set limits on the effective coupling of the b quark to the A 0 .
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.
We report a Dalitz plot analysis of charmless hadronic decays of charged B mesons to the final state KS0π+π0 using the full BABAR data set of 470.9±2.8 million BB¯ events collected at the Υ(4S) ...resonance. We measure the overall branching fraction and CP asymmetry to be B(B+→K0π+π0)=(31.8±1.8±2.1−0.0+6.0)×10−6 and ACP(B+→K0π+π0)=0.07±0.05±0.03−0.03+0.02, where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for B+→K0π+π0. We find first evidence of a CP asymmetry in B+→K*(892)+π0 decays: ACP(B+→K*(892)+π0)=−0.52±0.14±0.04−0.02+0.04. The significance of this asymmetry, including systematic and model uncertainties, is 3.4 standard deviations. We also measure the branching fractions and CP asymmetries for three other intermediate decay modes.
We search for a low-mass scalar C P -odd Higgs boson, A 0 , produced in the radiative decay of the upsilon resonance and decaying into a τ + τ − pair: Υ ( 1 S ) → γ A 0 . The production of Υ ( 1 S ) ...mesons is tagged by Υ ( 2 S ) → π + π − Υ ( 1 S ) transitions, using a sample of ( 98.3 ± 0.9 ) × 10 6 Υ ( 2 S ) mesons collected by the BABAR detector. We find no evidence for a Higgs boson in the mass range 3.5 ≤ m A 0 ≤ 9.2 GeV , and combine these results with our previous search for the tau decays of the light Higgs in radiative Υ ( 3 S ) decays, setting limits on the coupling of A 0 to the b ¯ b quarks in the range 0.09-1.9. Our measurements improve the constraints on the parameters of the next-to-minimal-supersymmetric Standard Model and similar theories with low-mass scalar degrees of freedom.