Measurement of the branching fractions of the B+ -> eta l(+)nu(l) and B+ -> eta ' l(+)nu(l) decays with signal-side only reconstruction in the full q(2) range

The branching fractions of the decays B+ -> eta l(+)nu(l) and B+ -> eta'l(+)nu(l) are measured, where l is either an electron or a muon, using a data sample of 711 fb(-1) containing 772 x 10(6)B (B) over bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. To reduce the dependence of the result on the form factor model, the measurement is performed over the entire q(2) range. The resulting branching fractions are B(B+ -> eta l(+)nu(l)) = (2.83 +/- 0.55((stat.)) +/- 0.34((syst.))) x 10(-5) and B(B+ -> eta'l(+)nu(l)) = (2.79 +/- 1.29((stat.)) +/- 0.30((syst.))) x 10(-5).journal articl

Precision Measurement of the Ratio Β(Y(3\u3ci\u3eS\u3c/i\u3e) → τ \u3csup\u3e+\u3c/sup\u3e τ\u3csup\u3e−\u3c/sup\u3e) / Β( Y(3\u3ci\u3eS\u3c/i\u3e)→ μ\u3csup\u3e+\u3c/sup\u3e μ\u3csup\u3e−

We report on a precision measurement of the ratio Rϒð3SÞ τμ ¼ Bðϒð3SÞ → τþτ−Þ=Bðϒð3SÞ → μþμ−Þ using data collected with the BABAR detector at the SLAC PEP-II eþe− collider. The measurement is based on a 28 fb−1 data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million ϒð3SÞ mesons. The ratio is measured to be Rϒð3SÞ τμ ¼ 0.966 0.008stat 0.014syst and is in agreement with the standard model prediction of 0.9948 within 2 standard deviations. The uncertainty in Rϒð3SÞ τμ is almost an order of magnitude smaller than the only previous measurement