Alexey Pak

Mass effects in muon and semileptonic b-->c decays.

Quantum chromodynamics (QCD) effects in the semileptonic decay b-->clnu are evaluated to the second order in the coupling constant, O(alpha(s){2}), and to several orders in the expansion in quark masses, m{c}/m{b}. Corrections are calculated for the total decay rate as well as for the first two moments of the lepton energy and the hadron system energy distributions. Translated into QED and applied to the muon decay, they decrease its predicted rate by -0.43 ppm.

Heavy-to-heavy quark decays at next-to-next-to-leading order

X iv :0 80 8. 35 09 v1 [ he pph ] 2 6 A ug 2 00 8 Alberta Thy 10-08 Heavy-to-heavy quark de ays at NNLO Alexey Pak and Andrzej Czarne ki Department of Physi s, University of Alberta, Edmonton, AB, T6G 2G7, Canada Details of a re ent al ulation of O`αs ́ orre tions to the de ay b → clνl, taking into a ount the c-quark mass, are des ribed. Constru tion of the expansion in the mass ratio mc/mb as well as the evaluation of new four-loop master integrals are presented. The same te hniques are appli able to the muon de ay, μ → eνμν̄e. Analyti al results are presented, for the physi al ases as well as for a model with purely-ve tor ouplings.

Two-loop QCD corrections to semileptonic b-quark decays near maximum recoil

Two-gluon radiative corrections to the b{yields}cl{nu}{sub l} decay width have been computed analytically as an expansion in terms of (m{sub c}/m{sub b})<<1 in the kinematical limit of zero lepton invariant mass. The obtained results match smoothly with a previously known expansion around (1-(m{sub c}/m{sub b}))<<1. Together they describe the process b{yields}cl{nu}{sub l} for all mass ratios (m{sub c}/m{sub b})

Charge asymmetries in \gamma\gamma \to \ell^+\ell^-+ \nu's (\ell=\mu, e) with polarized photons in the Standard Model

It is shown that in reaction \gamma\gamma\to\ell^+\ell^-+\nus at \sqrt{s}>200 GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative charged leptons (\ell=\mu^\pm, e^\pm), (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate \tau-lepton in \gamma \gamma \to W^\pm\ell^\mp + \nus reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the Photon Collider mode of the future international linear collider.

Large mass expansion in two-loop QCD corrections of paracharmonium decay

We calculate the two-loop QCD corrections to paracharmonium decays {eta}{sub c}{yields}{gamma}{gamma} and {eta}{sub c}{yields}gg involving light-by-light scattering diagrams with light quark loops. Artificial large mass expansion and convergence improvement techniques are used to evaluate these corrections. The obtained corrections to the decays {eta}{sub c}{yields}{gamma}{gamma} and {eta}{sub c}{yields}gg account for -1.25% and -0.73% of the leading order contribution, respectively.

Charge asymmetries in γ γ → l + l − + ν ’s ( l = μ , e ) with polarized photons in the standard model

It is shown that in reaction \gamma\gamma\to\ell^+\ell^-+\nus at \sqrt{s}>200 GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative charged leptons (\ell=\mu^\pm, e^\pm), (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate \tau-lepton in \gamma \gamma \to W^\pm\ell^\mp + \nus reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the Photon Collider mode of the future international linear collider.

Charge asymmetries in gamma gamma ---> l+ l- + nu's (l = mu, e) with polarized photons in the Standard Model

It is shown that in reaction \gamma\gamma\to\ell^+\ell^-+\nus at \sqrt{s}>200 GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative charged leptons (\ell=\mu^\pm, e^\pm), (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate \tau-lepton in \gamma \gamma \to W^\pm\ell^\mp + \nus reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the Photon Collider mode of the future international linear collider.