Hsiang-nan Li

Perturbative QCD analysis of B meson decays.

The resummation of large QCD radiative corrections, including leading and next-to-leading logarithms, in the pion electromagnetic form factor is reviewed. A similar formalism is applied to exclusive processes involving heavy mesons, and leads to Sudakov suppression for the semileptonic decay {ital B}{r_arrow}{pi}{ital l}{nu}. It is found that, with the inclusion of Sudakov effects, a perturbative QCD analysis of this decay is reliable for the energy fraction of the pion above 0.4. Combining predictions from soft pion theorems we estimate that the upper limit of the matrix element {parallel}{ital V}{sub {ital ub}}{parallel} is 2.8{endash}4.8{times}10{sup {minus}3} from different models of the {ital B} meson wave function. {copyright} {ital 1996 The American Physical Society.}

Factorization theorems, effective field theory, and nonleptonic heavy meson decays

The nonleptonic heavy meson decays B → D (∗) π(ρ), J/ψK (∗) and D → K (∗) π are studied based on the three-scale perturbative QCD factorization theorem developed recently. In this formalism the Bauer-Stech-Wirbel parameters a1 and a2 are treated as the Wilson coefficients, whose evolution from the W boson mass down to the characteristic scale of the decay processes is determined by effective field theory. The evolution from the characteristic scale to a lower hadronic scale is formulated by the Sudakov resummation. The scale-setting ambiguity, which exists in the conventional approach to nonleptonic heavy meson decays, is moderated. Nonfactorizable and nonspectator contributions are taken into account as part of the hard decay subamplitudes. Our formalism is applicable to both bottom and charm decays, and predictions, including those for the ratios R and RL associated with the B → J/ψK (∗) decays, are consistent with experimental data.

Three-scale factorization theorem and effective field theory: Analysis of nonleptonic heavy meson decays

We develop a perturbative QCD factorization theorem which is compatible with effective field theory. The factorization involves three scales: an infrared cutoff of order

Resummation in hard QCD processes

{\ensuremath{\Lambda}}_{\mathrm{QCD}},

Perturbative QCD study of B → D ( * ) decays

a hard scale of the order of the

Determination of the heavy quark effective theory parameters from the B → X s γ decay

B

Determination of the HQET parameters from the B ---> X(s) gamma decay

meson mass, and an ultraviolet cutoff of the order of the

InternalW-emission andW-exchange contributions toB→D(*)decays

W

Scaling of Aharonov-Bohm couplings and the dynamical vacuum in gauge theories

boson mass. Our approach is renormalization-group invariant and moderates the scale-dependent problem in effective field theory. Employing this formalism with nonfactorizable contributions included, we clarify the controversy over the BSW parameters

PQCD analysis of inclusive semileptonic decays of B mesons.

{a}_{2}{/a}_{1}