Current Topics in B Physics

I discuss topics of particular interest in connection with the ongoing experiments at the B factories BaBar and Belle: B-mixing, QCD effects in nonleptonic decays and rare decays.Comment: Plenary Talk given at IVth Rencontres de Vietnam, Hanoi, July 2000; 10 page

Implication of the D^0 Width Difference On CP-Violation in D^0-\bar D^0 Mixing

Both BaBar and Belle have found evidence for a non-zero width difference in the $D^0$-$\bar D^0$ system. Although there is no direct experimental evidence for CP-violation in $D$ mixing (yet), we show that the measured values of the width difference $y\sim \Delta\Gamma$ already imply constraints on the CP-violating phase in $D$ mixing, which, if significantly different from zero, would be an unambiguous signal of new physics.Comment: 9 pages; typos remove

Spontaneous CP Violation in the Left-Right-Symmetric Model

We investigate the pattern of CP violation in \Kd, \Bd and \Bs mixing in a symmetrical \model model with spontaneous CP violation. Performing a careful analysis of all relevant restrictions on the model's parameters from $\Delta M_K$, $\Delta M_{B_d}$, $\Delta M_{B_s}$, $\epsilon_K$, the sign of \ee and the mixing-induced CP asymmetry in \goldd, we find that the mass of the right-handed charged gauge-boson, $M_2$, is restricted to be in the range 2.75 to 13$$TeV, and that the mass of the flavour-changing neutral-Higgs bosons, $M_H$, must be between 10.2 to 14.6$$TeV. We also find that the model, although still compatible with present experimental data, cannot accomodate the SM prediction of large CP violation in \goldd, but, on the other hand, predicts a large CP-asymmetry of ${\cal O}(40$ in \golds. These specific predictions make it possible to submit the model to a scrupulous test at B factories and hadron colliders.Comment: 8 pages, 7 figures, talk given at Moriond2000 E

∣Vcb∣|V_{cb}| from inclusive semileptonic B decays

We determine $|V_{cb}|$ from inclusive semileptonic B decays including resummation of supposedly large perturbative corrections, which originate from the running of the strong coupling. We argue that the low value of the BLM scale found previously for inclusive decays is a manifestation of the renormalon divergence of the perturbative series starting already in third order. A reliable determination of $|V_{cb}|$ from inclusive decays is still possible if one uses a short-distance b quark mass. We find that using the $\overline{\rm MS}$ running mass significantly reduces the perturbative coefficients already in low orders. For a semileptonic branching ratio of $10.9\%$ we obtain $|V_{cb}|(\tau_B/1.50\,{\rm ps})^{1/2}=0.041\pm 0.002\pm 0.002$. This work was done in collaboration with M. Beneke and V.M.\ Braun.Comment: 6 pages, plain Latex (a4wide.sty and epsf.sty required). One postscript figure in uuencoded gzip format. To appear in the Proceedings of the XXXth Rencontres de Moriond, ``QCD and High Energy Hadronic Interactions'', Les Arcs, France, March 199

B decays into light mesons

I calculate the form factors describing semileptonic and penguin induced decays of B mesons into light pseudoscalar and vector mesons. The form factors are calculated from QCD sum rules on the light-cone including contributions up to twist 4, radiative corrections to the leading twist contribution and SU(3) breaking effects. The theoretical uncertainty is estimated to be $\sim$ (15-20)%.Comment: 8 pages latex plus one figure; invited talk at Moriond QCD 9

The most promising ways to measure V_ub

I review currently discussed methods to determine the CKM mixing matrix element $|V_{ub}|$ from experimental data. Although the theory of inclusive decays and their spectra has entered a model-independent stage, its predictions are still sensitive to various input parameters, in particular the poorly known $b$ quark mass. At present, determinations from exclusive channels, notably $B\to\pi e \nu$, seem slightly more accurate and allow determination of $|V_{ub}|$ from the spectrum in the momentum transfer to the leptons with a theoretical uncertainty of $\sim 10$.Comment: 10 pages, LaTeX, 4 figures. Invited plenary talk given at the 7th International Symposium on Heavy Flavor Physics, Santa Barbara, California, 7-11 July 1997. To appear in the proceeding