1,985 research outputs found
Mixing of Pseudoscalar Mesons
Eta-eta' mixing is discussed in the quark-flavor basis with the hypothesis
that the decay constants follow the pattern of particle state mixing. On
exploiting the divergences of the axial vector currents - which embody the
axial vector anomaly - all mixing parameters are fixed to first order of flavor
symmetry breaking. An alternative set of parameters is obtained from a
phenomenological analysis. We also discuss mixing in the octet-singlet basis
and show how the relevant mixing parameters are related to those in the
quark-flavor basis. The dependence of the mixing parameters on the strength of
the anomaly and the amount of flavor symmetry breaking is investigated.
Finally, we present a few applications of the quark-flavor mixing scheme, such
as radiative decays of vector mesons, the photon-pseudoscalar meson transition
form factors, the coupling constants of eta and eta' to nucleons, and the
isospin-singlet admixtures to the pi^0 meson.Comment: 21 pages, 6 figures, Proc. WORKSHOP ON ETA PHYSICS, Uppsala, October
22-27, 200
The Overlap Representation of Skewed Quark and Gluon Distributions
Within the framework of light-cone quantisation we derive the complete and
exact overlap representation of skewed parton distributions for unpolarised and
polarised quarks and gluons. Symmetry properties and phenomenological
applications are discussed.Comment: LaTex, 36 pages. v2: incorrect paper attached originally. v3: erratum
adde
Proton mass effects in wide-angle Compton scattering
We investigate proton mass effects in the handbag approach to wide-angle
Compton scattering. We find that theoretical uncertainties due to the proton
mass are significant for photon energies presently studied at Jefferson Lab.
With the proposed energy upgrade such uncertainties will be clearly reduced.Comment: 4 pages, uses revtex, 3 figure
Quark model description of quasi-elastic pion knockout from the proton at JLAB
The interference term between s- and t-pole contributions to the p(e,e' pi+)n
cross section is evaluated on the basis of the constituent quark model. It is
shown that the contribution of baryon s-poles can be modeled by a nonlocal
extension of the Kroll-Rudermann contact term. This contribution is in a
destructive interference with the pion t-pole that is essential to improve the
description of recent JLab data at the invariant mass W=1.95 GeV. Some
predictions are made for a new JLab measurement at higher values W=2.1-2.3 GeV
and Q2 centered at 1.6 and 2.45 GeV2/c2.Comment: 15 pages, 4 figures, to be published in Phys. Lett.
Symmetry-breaking corrections to heavy-to-light B meson form factors at large recoil
Recently it has been shown that symmetries emerging in the heavy quark and
large recoil energy limit impose various relations on form factors that
parametrise the decay of B mesons into light mesons. These symmetries are
broken by perturbative effects. In this paper we discuss the structure of
heavy-to-light form factors including such effects and compute
symmetry-breaking corrections to first order in the strong coupling. As an
application of our results we consider the forward-backward asymmetry zero in
the rare decay B -> V l^+ l^- and the possibility to constrain potential new
physics contributions to the Wilson coefficient C_9.Comment: 30 pages, LaTeX (typos in eq. (44), (46) corrected
Phenomenology of eta-gamma and eta'-gamma transition form factors at large momentum transfer
I discuss the progress in our theoretical understanding of the eta-gamma and
eta'-gamma transition form factors, including the recent data from CLEO and L3
at large momentum transfer, Q^2. The experimental data above Q^2=1 GeV^2 can be
well described by the hard scattering approach if the distribution amplitudes
for eta and eta' mesons are taken close to the asymptotic one. Particular
attention is paid to the interpretation of the data in terms of properly
defined eta-eta' mixing parameters. I also comment on the use and misuse of
interpolation formulas for P-gamma and P-gamma^* transition form factors.Comment: 6 pages + 4 figures (using espcrc2.sty, feynmp.sty); Talk presented
at conference PHOTON'99, Freiburg, May 199
How much charm can PANDA produce?
We consider the production of charmed baryons and mesons in the
proton-antiproton binary reactions at the energies of the future ANDA
experiment. To describe these processes in terms of hadronic interaction
models, one needs strong couplings of the initial nucleons with the
intermediate and final charmed hadrons. Similar couplings enter the models of
binary reactions with strange hadrons. For both charmed and strange hadrons we
employ the strong couplings and their ratios calculated from QCD light-cone sum
rules. In this method finite masses of and quarks are taken into
account. Employing the Kaidalov's quark-gluon string model with Regge poles and
adjusting the normalization of the amplitudes in this model to the calculated
strong couplings, we estimate the production cross section of charmed hadrons.
For it can reach several tens of at
, whereas the cross sections of and pair
production are predicted to be smaller.Comment: 22 pages, 6 figures, matches published versio
Dilepton production by bremsstrahlung of meson fields in nuclear collisions
We study the bremsstrahlung of virtual omega mesons due to the collective
deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion
collision. It is shown that electromagnetic decays of these mesons may give an
important contribution to the observed yields of dileptons. Mass spectra of
positron-electron and muon pairs produced in central Au+Au collisions are
calculated under some simplifying assumptions on the space-time variation of
the baryonic current in a nuclear collision process. Comparison with the CERES
data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a
noticeable fraction of the observed lepton pairs in the intermediate region of
invariant masses. Sensitivity of the dilepton yield to the in-medium
modification of masses and widths of vector mesons is demonstrated.Comment: 14 page
Helicity-Flip Off-Foward Parton Distributions of the Nucleon
We identify quark and gluon helicity-flip distributions defined between
nucleon states of unequal momenta. The evolution of these distributions with
change of renormalization scale is calculated in the leading-logarithmic
approximation. The helicity-flip gluon distributions do not mix with any quark
distribution and are thus a unique signature of gluons in the nucleon. Their
contribution to the generalized virtual Compton process is obtained both in the
form of a factorization theorem and an operator product expansion. In deeply
virtual Compton scattering, they can be probed through distinct angular
dependence of the cross section.Comment: a few corrections made, references change
- …