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Register a new userStudies of tau- -> eta.K-.nu and tau- -> eta.pi-.nu at BaBar and a search for a second-class current
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We report on analyses of tau lepton decays $tau^- to eta K^- u_{tau}$ and $tau^- to eta pi^- u_{tau}$, with $eta to pi^+ pi^- pi^0$, using 470 fb$^{-1}$ of data from the Babar experiment at PEP-II, collected at center-of-mass energies at and near the $Upsilon(4S)$ resonance. We measure the branching fraction for the $tau^- to eta K^- u_{tau}$ decay mode, $Br(tau^- to eta K^- u_{tau}) = (1.42pm0.11text{(stat)}pm0.07text{(syst)})times10^{-4}$, and report a 95% confidence level upper limit for the second-class current process $tau^- to eta pi^- u_{tau}$, $Br(tau^- to eta pi^- u_{tau}) < 9.9times10^{-5}$.
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The measurement of B->tau nu at the B factories provides important constraints on the parameter tan beta/m_H^+- in the context of models with two Higgs doublets. Limits on this decay from e+e- collisions at the Z peak were sensitive to the sum of B->tau nu and B_c->tau nu. Due to the possibly sizeable contribution from B_c->tau nu we suggest that a signal for this combination might be observed if the LEP L3 Collaboration used their total data of ~3.6 10^6 hadronic decays of the Z boson. Moreover, we point out that a future Linear Collider operating at the Z peak (Giga Z option) could constrain tan beta/m_H^+- from the sum of these processes with a precision comparable to that anticipated at proposed high luminosity B factories from B-> tau nu alone.
We report an analysis of tau- decaying into omega.pi-.nu_tau with omega -> pi+pi-pi0 using a data sample containing nearly 320 million tau pairs collected with the BABAR detector at the PEP-II B-Factory. We find no evidence for second-class currents and we set an upper limit of 0.69% at 90% confidence level for the fraction of second-class currents in this decay mode.
We present a search for the decay B+ -> tau+ nu using 288 inverse femtobarns of data collected at the Upsilon(4S) resonance with the BaBar detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed semileptonic B decay (B- -> D0 l- nu X) is selected, and in the recoil a search for the signal decay mode is performed. The tau is identified in four channels. We measure a branching fraction of BF(B+ -> tau+ nu) = (0.88+0.68 -0.67(stat.) +- 0.11(syst.)) x 10^{-4} and extract an upper limit on the branching fraction, at the 90% confdence level, of 1.8 x 10^{-4}.
We evaluate the compositeness effects of tau lepton on the vertex W-tau-nu(tau) in the context of an effective Lagrangian approach. We consider that only the third family is composed and we get the corrections to the non universal lepton coupling g_(tau)/g_(e). As the experimental bounds on non universal lepton couplings in W decays are weak, we find that the excited particles contributions do not give realistic limits on the excited mass, since they lead to Lambda<m*.
We present a search for the decays B+ -> mu+ nu_mu and B+ -> e+ nu_e in a 253 fb-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy B factory. We find no significant evidence for a signal and set 90% confidence level upper limits of B(B+ -> mu+ nu_mu) < 1.7 x 10^{-6} and B(B+ -> e+ nu_e) < 9.8 x 10^{-7}.
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