1,432 research outputs found
Radial excitations of heavy-light mesons from QCD sum rules
QCD sum rules are commonly used to predict the characteristics of
ground-state hadrons. We demonstrate that two-point sum rules for the decay
constants of charmed () and bottom ()
mesons can also be modified to estimate the decay constants of the first radial
excitations, and , respectively,
provided the masses of these resonances are used as an input. For the radially
excited charmed mesons we use available experimental data, whereas the masses
of analogous bottom mesons are estimated from the heavy-quark limit. The decay
constants predicted for the radial excitations of heavy-light pseudoscalar and
vector mesons are systematically smaller than those of the ground states and we
comment on the possible origin of this difference. Our results can be used in
the sum rule calculations of heavy-to-light form factors and in the
factorization approximations for nonleptonic -meson decays where the decay
constants of charmed mesons enter as input parameters.Comment: 16 pages, a few comments added, version to appear in EPJ
The Challenge of Light-Front Quantisation: Recent Results
We explain what is the challenge of light-front quantisation, and how we can
now answer it because of recent progress in solving the problem of zero modes
in the case of non-Abelian gauge theories. We also give a description of the
light-front Hamiltonian for SU(2) finite volume gluodynamics resulting from
this recent solution to the problem of light-front zero modes.Comment: 17 pages, lecture delivered by GBP at the XXXIV PNPI Winter School,
Repino, St.Petersburg, Russia, February 14-20, 2000, version to appear in the
Proceeding
Next-to-Leading Order perturbative QCD corrections to baryon correlators in matter
We compute the next-to-leading order perturbative QCD corrections to the
correlators of nucleon interpolating currents in relativistic nuclear matter.
The main new result is the calculation of the O(alpha_s) perturbative
corrections to the coefficient functions of the vector quark condensate in
matter. This condensate appears in matter due to the violation of Lorentz
invariance. The NLO perturbative QCD corrections turn out to be large which
implies that the NLO corrections must be included in a sum rule analysis of the
properties of both bound nucleons and relativistic nuclear matter.Comment: 19 pages in LaTeX, including 5 Postscript figure
Parton Scattering at Small-x and Scaling Violation
Scaling violation of inclusive jet production at small- in hadron scattering with increasing total collision energy is discussed. Perturbative QCD based on the factorisation theorem for hard processes and GLAPD evolution equations predicts a minimum for scaled cross-section ratio that depends on jet rapidity. Studies of such a scaling violation can reveal a vivid indication of new dynamical effects in the high-energy limit of QCD. The BFKL effects, which seem to be seen in recent L3 data at CERN LEP2, should give different results from GLAPD predictions.Scaling violation of inclusive jet production at small- in hadron scattering with increasing total collision energy is discussed. Perturbative QCD based on the factorisation theorem for hard processes and GLAPD evolution equations predicts a minimum for scaled cross-section ratio that depends on jet rapidity. Studies of such a scaling violation can reveal a vivid indication of new dynamical effects in the high-energy limit of QCD. The BFKL effects, which seem to be seen in recent L3 data at CERN LEP2, should give different results from GLAPD predictions
Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation
We used high order harmonics of a femtosecond titanium-doped sapphire system
(pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS)
measurements on diamond. The UPS spectra were measured for harmonics in the
range 13 to 27. We also made ab initio calculations of the electronic lifetime
of conduction electrons in the energy range produced in the UPS experiment.
Such calculations show that the lifetime suddenly diminishes when the
conduction electron energy reaches the plasmon energy, whereas the UPS spectra
show evidence in this range of a strong relaxation mechanism with an increased
production of low energy secondary electrons. We propose that in this case the
electronic relaxation proceeds in two steps : excitation of a plasmon by the
high energy electron, the latter decaying into individual electron-hole pairs,
as in the case of metals. This process is observed for the first time in an
insulator and, on account of its high efficiency, should be introduced in the
models of laser breakdown under high intensity
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