Ultrasoft contribution to heavy-quark pair production near threshold

We compute the third-order correction to the heavy-quark current correlation function due to the emission and absorption of an ultrasoft gluon. Our result supplies a missing contribution to top-quark pair production near threshold and the determination of the bottom quark mass from QCD sum rules.Comment: 10 pages, LaTe

Spectator scattering at NLO in non-leptonic B decays: Tree amplitudes

We compute the 1-loop (alpha_s^2) correction to hard spectator scattering in non-leptonic B decay tree amplitudes. This forms part of the NNLO contribution to the QCD factorization formula for hadronic B decays, and introduces a new rescattering phase that corrects the leading-order result for direct CP asymmetries. Among the technical issues, we discuss the cancellation of infrared divergences, and the treatment of evanescent four-quark operators. The infrared finiteness of our result establishes factorization of spectator scattering at the 1-loop order. Depending on the values of hadronic input parameters, the new 1-loop correction may have a significant impact on tree-dominated decays such as B -> pi pi.Comment: 28 pages, 5 figures, LaTe

Top quark production near threshold

The present theoretical status of top quark pair production near threshold at (future) $e^+ e^-$ ($\mu^+\mu^-$) colliders is summarized.Comment: 8 pages, LaTeX, Talk presented at the High Energy Physics International Euroconference on Quantum Chromodynamics (QCD'99), Montpellier, France, 7-13 July 199

Third-order non-Coulomb correction to the S-wave quarkonium wave functions at the origin

We compute the third-order correction to the S-wave quarkonium wave functions |\psi_n(0)|^2 at the origin from non-Coulomb potentials in the effective non-relativistic Lagrangian. Together with previous results on the Coulomb correction and the ultrasoft correction computed in a companion paper, this completes the third-order calculation up to a few unknown matching coefficients. Numerical estimates of the new correction for bottomonium and toponium are given.Comment: 12 pages, v2: matches published version, missing factors in eq. (9), (29) adde

Top quark production near threshold and the top quark mass

We consider top-anti-top production near threshold in $e^+ e^-$ collisions, resumming Coulomb-enhanced corrections at next-to-next-to-leading order (NNLO). We also sum potentially large logarithms of the small top quark velocity at the next-to-leading logarithmic level using the renormalization group. The NNLO correction to the cross section is large, and it leads to a significant modification of the peak position and normalization. We demonstrate that an accurate top quark mass determination is feasible if one abandons the conventional pole mass scheme and if one uses a subtracted potential and the corresponding mass definition. Significant uncertainties in the normalization of the $t\bar{t}$ cross section, however, remain.Comment: 14 pages, LaTeX, 2 figures included via epsf.st

Correlator of heavy-quark currents at small q^2 in the large-beta_0 limit

The correlator of vector heavy-quark currents at small q^2 is considered in the large-beta_0 limit. The leading IR renormalon ambiguity of the sum of the perturbative series is canceled by the UV renormalon ambiguity of the gluon condensate. Asymptotic behaviour of the perturbative series is obtained in a model-independent way, up to a single unknown normalization factor. Gluon-virtuality distribution functions for the perturbative correction are calculated.Comment: 8 pages, 3 figure

Power corrections in heavy-to-light decays at large recoil energy

I briefly present recent work on QCD power corrections in heavy-to-light meson decays, using an effective field theory approach.Comment: 4 pages, 1 figure. Talk given at ICHEP 2002, Amsterdam, July 200

Estimates of flavoured scalar production in B - decays

Estimates are presented for the branching ratios of several two-particle B-meson decays into flavoured scalar mesons.Comment: 6 pages, Latex, no figures; small improvement

Theory of hadronic B decays

I give an overview of the theory of hadronic nonleptonic B decays into two light mesons. Using the soft-collinear effective theory (SCET), a factorization theorem for these processes has been proven to leading order in 1/mb. The phenomenological implications of this factorization relation for B-> \pi\pi decays are discussed, together with the prospects for determining the weak phase \alpha(\phi_2) from these modes.Comment: Contribution to the 3rd Conference on Flavor Physics and CP Violation (FPCP04), Daegu, Korea; 9 pages, 2 figure