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V. M. Braun

Publications and source records attributed to V. M. Braun.

130 records · Page 8Linked to original sources
arXiv1993

Instanton contributions to the $τ$ decay widths

Contrary to some previous claims, we find a sizable instanton contribution to the finite energy sum rule used to extract the value of the strong coupling from the measured $τ$ decay widths. It is of the same order of magnitude as standard nonperturbative corrections induced by vacuum quark and gluon condensates. Our result indicates that there might be no hierarchy of power corrections in finite energy sum rules at the scale of $τ$ mass. Therefore, the standard nonperturbative corrections do not necessarily improve the accuracy of the theoretical predicition, but can rather be used to estimate an intrinsic accuracy of the pure perturbative calculation, which turns out to be rather high on this evidence, of order one percent.

hep-ph↗
arXiv1993

Next--to--Leading Order Corrections to Meson Masses in the Heavy Quark Effective Theory

We use the QCD sum rule approach to calculate the splitting between vector and pseudoscalar mesons containing one light and one heavy quark, and the kinetic energy of the heavy quark. Our result for the splitting induced by the chromomagnetic interaction agrees to the experimental data on charm and beauty mesons. For the matrix element of the kinetic energy operator, we obtain the value $K=-(0.60\pm 0.10)\, {\rm GeV}^2$.

hep-ph↗
arXiv1993

Semileptonic Inclusive B--Decays and the Determination of $|V_{ub}|$ from QCD Sum Rules

We calculate the electron spectrum of semileptonic decays of B-mesons into non-charmed hadrons. The shape of the spectrum obtained from QCD sum rules is in general agreement with quark model calculations. At high electron energies the decrease of the spectrum is less steep than predicted by Altarelli et al. Our analysis yields a total decay rate $Γ(B\to X_u e\barν) = (6.8\pm 2.0) 10^{13} |V_{ub}|^2 {s}^{-1}$. For the spectrum integrated over electron energies in the interval $2.4{ GeV}\leq E_e \leq 2.6\mbox{\ GeV}$ in the laboratory frame we obtain $Γ(B\to X_u e \barν)= (5.0\pm 1.6) 10^{12} |V_{ub}|^2 {s}^{-1}$. Estimating all sorts of theoretical uncertainties, we obtain $|V_{ub}| = 0.003\pm 0.001$ for the $b \to u$ weak transition matrix element from the new CLEO-data.

hep-ph↗