Speaker
Stefan Alte
(Johannes Gutenberg University, Mainz, Germany)
Description
We present a detailed theoretical analysis of very rare, exclusive
hadronic decays of Z bosons from first principles of QCD. Our main
focus is on the radiative decays Z -> M gamma, in which M is a
pseudoscalar or vector meson. At leading order in an expansion in
powers of Lambda_QCD/mV the decay amplitudes can be factorized into
convolutions of calculable hard-scattering coefficients with the
leading-twist light-cone distribution amplitude of the meson M. Power
corrections to the decay rates arise first at order (Lambda_QCD/mV
)^2. They can be estimated in terms of higher-twist distribution
amplitudes and are predicted to be tiny. We include one-loop
O(alpha_s) radiative corrections to the hard-scattering coefficients
and perform the resummation of large logarithms (alpha_s
ln(m_V^2/mu_0^2))^n (with mu_0 \approx 1 GeV a typical hadronic scale)
to all orders in perturbation theory. Evolution effects have an
important impact both numerically and conceptually, since they reduce
the sensitivity to poorly determined hadronic parameters. We also
discuss the special case where M has a flavor singlet component on its
wavefunction. A measurement of these processes at a future
high-luminosity Z factory could provide interesting information on the
gluon distribution amplitude. Some of the decay modes studied here
have branching ratios large enough to be accessible in the
high-luminosity run of the LHC. Many of them can be measured with
high accuracy at a future lepton collider. This will provide
stringent tests of the QCD factorization formalism and enable novel
searches for new physics.
Author
Stefan Alte
(Johannes Gutenberg University, Mainz, Germany)
