Radiative and leptonic decays of B-mesons represent an excellent laboratory for the search for New Physics. I present here recent results on radiative and leptonic decays from the Belle and BABAR collaborations. Radiative penguin and leptonic B-meson decays are excellent probes for investigating the effects of New Physics. Although current measurements are in agreement with the Standard Model expectations, they are still quite useful for setting bounds on possible NP models. The B → X{sub s}[gamma] and B → [tau][nu] measurements, for example, put strong constraints on the mass of charged Higgs bosons in Type II two-Higgs double models. The B → X{sub s}[gamma] branching fraction measurements also constrain models with universal extra dimensions.

This 2nd edition is an extensive update of 'B Decays”. The revisions are necessary because of the extensive amount of new data and new theoretical ideas. This book reviews what is known about b-quark decays and also looks at what can be learned in the future.The importance of this research area is increasing, as evidenced by the approval of the luminosity upgrade for CESR and the asymmetric B factories at SLAC and KEK, and the possibility of experiments at hadron colliders.The key experimental observations made thus far, measurement of the lifetimes of the different B species, B0-B0 mixing, the discovery of “Penguin” mediated decays, and the extraction of the CKM matrix elements Vub and Vcb from semileptonic decays, as well as more mundane results, are described in great detail by the experimentalists who have been closely involved with making the measurements. Theoretical progress in understanding b-quark decays using HQET and lattice gauge techniques are described by theorists who have developed and used these techniques.Synthesizing the experimental and theoretical information, several articles discuss the implications for the “Standard Model” and how further tests can be done using measurements of CP violation in the B system.

We present the results of a search for B+ meson decays into [gamma]l+vl, where l = e, [mu]. We use a sample of 232 million B$\bar{B}$ meson pairs recorded at the [Upsilon](4S) resonance with the BABAR detector at the PEP-II B factory. We measure a partial branching fraction [Delta][beta] in a restricted region of phase space that reduces the effect of theoretical uncertainties, requiring the lepton energy to be in the range 1.875 and 2.850 GeV, the photon energy to be in the range 0.45 and 2.35 GeV, and the cosine of the angle between the lepton and photon momenta to be less than -0.36, with all quantities computed in the [Upsilon](4S) center-of-mass frame. We find [Delta][beta](B+ 2![gamma]l+vl) = ( -0.31.5+1.3(statistical) -0.6+0.6(systematic) ± 0.1(theoretical)) x 10-6, under the assumption of lepton universality. Interpreted as a 90% confidence-level Bayesian upper limit, the result corresponds to 1.7 x 10-6 for a prior at in amplitude, and 2.3 x 10-6 for a prior at in branching fraction.