Evidence of the purely leptonic decay B- --> tau- nu(tau)

Towards the identification of new physics through quark flavour violating processes

We outline a systematic strategy that should help in this decade to identify new physics (NP) beyond the standard model (SM) by means of quark flavour violating processes, and thereby extend the picture of short distance physics down to scales as short as 10(-20) m and even shorter distance scales corresponding to energies of 100 TeV. Rather than using all of the possible flavour-violating observables that will be measured in the coming years at the LHC, SuperKEKB and in Kaon physics dedicated experiments at CERN, J-PARC and Fermilab, we concentrate on those observables that are theoretically clean and very sensitive to NP. Assuming that the data on the selected observables will be very precise, we stress the importance of correlations between these observables as well as of future precise calculations of non-perturbative parameters by means of lattice QCD simulations with dynamical fermions. Our strategy consists of twelve steps, which we will discuss in detail while illustrating the possible outcomes with the help of the SM, models with constrained minimal flavour violation (CMFV), MFV at large and models with tree-level flavour changing neutral currents mediated by neutral gauge bosons and scalars. We will also briefly summarize the status of a number of concrete models. We propose DNA charts that exhibit correlations between flavour observables in different NP scenarios. Models with new left-handed and/or right-handed currents and non-MFV interactions can be distinguished transparently in this manner. We emphasize the important role of the stringent CMFV relations between various observables as standard candles of flavour physics. The pattern of deviations from these relations may help in identifying the correct NP scenario. The success of this program will be very much facilitated through direct signals of NP at the LHC, even if the LHC will not be able to probe the physics at scales shorter than 4 × 10(-20) m. We also emphasize the importance of lepton flavour violation, electric dipole moments, and (g - 2)e, μ in these studies.

Evidence for B- → τ- ν(τ) with a hadronic tagging method using the full data sample of Belle

We measure the branching fraction of B- → τ- ν(τ) using the full Υ(4S) data sample containing 772×10(6) BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. Events with BB pairs are tagged by reconstructing one of the B mesons decaying into hadronic final states, and B- → τ- ν(τ) candidates are detected in the recoil. We find evidence for B- → τ- ν(τ) with a significance of 3.0 standard deviations including systematic errors and measure a branching fraction B(B- → τ- ν(τ))=[0.72(-0.25)(+0.27)(stat)±0.11(syst)]×10(-4).

Implications of lepton flavor universality violations in B decays

Present measurements of b→cτν and b→uτν transitions differ from the standard model predictions of lepton flavor universality by almost 4σ. We examine new physics interpretations of this anomaly. An effective field theory analysis shows that minimal flavor violating models are not preferred as an explanation, but are also not yet excluded. Allowing for general flavor violation, right-right vector and right-left scalar quark currents are identified as viable candidates. We discuss explicit examples of two Higgs doublet models, leptoquarks as well as quark and lepton compositeness. Finally, implications for LHC searches and future measurements at the (super-)B factories are presented.

Measurement of the absolute branching fraction of Ds+ --> tau+ nutau decay

Using a sample of tagged D(s)(+) decays collected near the D(s)(*+/-)D(s)(-/+) peak production energy in e(+)e(-) collisions with the CLEO-c detector, we study the leptonic decay D(s)(+)-->tau(+)nu(tau) via the decay channel tau(+)-->e(+)nu(e)nu(tau). We measure B(D(s)(+)-->tau(+)nu(tau))=(6.17+/-0.71+/-0.34)%, where the first error is statistical and the second systematic. Combining this result with our measurements of D(s)(+)-->mu(+)nu(mu) and D(s)(+)-->tau(+)nu(tau) (via tau(+)-->pi(+)nu(tau)), we determine f(D(s))=(274+/-10+/-5) MeV.

Light minimal supersymmetric standard model Higgs boson scenario and its test at hadron colliders

We show that, in the minimal supersymmetric standard model, the possibility for the lightest CP-even Higgs boson to be lighter than Z boson (as low as about 60 GeV) is, contrary to the usual belief, not yet excluded by the CERN LEP2 Higgs search nor any direct searches for supersymmetric particles at high energy colliders. The characteristic of the light Higgs boson scenario (LHS) is that the ZZh coupling and the decay branching ratio Br(h/A-->bb) are simultaneously suppressed as a result of generic supersymmetric loop corrections. Consequently, the W(+/-)H(-/+)h coupling has to be large due to the sum rule of Higgs couplings to weak gauge bosons. We discuss the potential of the Fermilab Tevatron and B factories to test the LHS, and show that the associated neutral and charged Higgs boson production process, pp-->H(+/-)h(A), can completely probe the LHS at the CERN Large Hadron Collider.

Search for B --> h(*)nunu[over ] decays at Belle

We present a search for the rare decays B --> h(*)nunu[over ], where h(*) stands for a light meson. A data sample of 535 x 10{6} BB[over ] pairs collected with the Belle detector at the KEKB e{+}e{-} collider is used. Signal candidates are required to have an accompanying B meson fully reconstructed in a hadronic mode and signal side particles consistent with a single h(*) meson. No significant signal is observed and we set upper limits on the branching fractions at 90% confidence level. The limits on B{0} --> K{*0}nunu[over ] and B{+} --> K{+}nunu[over ] decays are more stringent than the previous constraints, while the first searches for B{0} --> K{0}nunu[over ], pi{0}nunu[over ], rho{0}nunu[over ], varphinunu[over ] and B{+} --> K{*+}nunu[over ], rho{+}nunu[over ] are reported.

Observation of B(0)-->D(*-)tau(+)nu(tau) decay at Belle

We report an observation of the decay B{0}-->D{*-}tau{+}nu{tau} in a data sample containing 535x10{6} BB pairs collected with the Belle detector at the KEKB asymmetric-energy e{+}e{-} collider. We find a signal with a significance of 5.2sigma and measure the branching fraction B(B{0}-->D{*-}tau{+}nu{tau})=(2.02{-0.37}{+0.40}(stat)+/-0.37(syst))%. This is the first observation of an exclusive B decay with a b-->ctaunu{tau} transition.