6,904 research outputs found
Charm production in antiproton-nucleus collisions at the and the thresholds
We discuss the production of charmonium states in antiproton-nucleus
collisions at the threshold. It is explained that measurements in collisions will allow to get new information about the strengths of the
inelastic interaction, on the production of and
in charmonium-nucleon interactions and for the first time about
nondiagonal transitions . The inelastic -nucleon
cross section is extracted from the comparison of hadron-nucleus collisions
with hadron-nucleon collisions. We extract the total nucleon cross
section from photon-nucleon collisions by accounting for the color transparency
phenomenon within the frame of the GVDM (Generalized Vector meson Dominance
Model). We evaluate also within the GVDM the inelastic -nucleon cross
section as well as the cross section for the nondiagonal transitions.
Predictions for the ratio of to yields in antiproton-nucleus
scatterings close to the threshold of production for different nuclear
targets are presented.Comment: 13 pages, 10 figures, typos corrected, some discussion adde
Costituent Quark Picture out of QCD in two dimensions - on the Light-Cone
Using DLCQ as a nonperturbative method, we test Fock-space truncations in
by studying the mass spectra of hadrons in colour SU(2) and
SU(3) at finite harmonic resolution . We include states
for mesons and up to states for baryons. With this truncation, we
give `predictions' for the masses of the first five states where finite
effects are minimal.Comment: 13 pages, uses elsart.sty 2 Postscript figures, uses epsf.sty
'elsart.sty' and 'elsart12.sty' are available via anonymous-ftp at
ftp://ftp.tex.ac.uk/tex-archive/macros/latex/contrib/supported/elsevie
Novel Six-Quark Hidden-Color Dibaryon States in QCD
The recent observation of a hadronic resonance in the proton-neutron
system with isospin and spin-parity raises the possibility
of producing other novel six-quark dibaryon configurations allowed by QCD. A
dramatic example of an exotic six-quark color-singlet system is the charge
, isospin I=3, state which couples strongly to
+ The width and decay properties of such
six-quark resonances could be regarded as manifestations of "hidden-color"
six-quark configurations, a first-principle prediction of QCD -- SU(3)-color
gauge theory for the deuteron distribution amplitude. Other implications and
possible future experiments are discussed
Light-Cone Quantization and Hadron Structure
In this talk, I review the use of the light-cone Fock expansion as a
tractable and consistent description of relativistic many-body systems and
bound states in quantum field theory and as a frame-independent representation
of the physics of the QCD parton model. Nonperturbative methods for computing
the spectrum and LC wavefunctions are briefly discussed. The light-cone Fock
state representation of hadrons also describes quantum fluctuations containing
intrinsic gluons, strangeness, and charm, and, in the case of nuclei, "hidden
color". Fock state components of hadrons with small transverse size, such as
those which dominate hard exclusive reactions, have small color dipole moments
and thus diminished hadronic interactions; i.e., "color transparency". The use
of light-cone Fock methods to compute loop amplitudes is illustrated by the
example of the electron anomalous moment in QED. In other applications, such as
the computation of the axial, magnetic, and quadrupole moments of light nuclei,
the QCD relativistic Fock state description provides new insights which go well
beyond the usual assumptions of traditional hadronic and nuclear physics.Comment: LaTex 36 pages, 3 figures. To obtain a copy, send e-mail to
[email protected]
High-Energy QCD Asymptotics of Photon-Photon Collisions
The high-energy behaviour of the total cross section for highly virtual
photons, as predicted by the BFKL equation at next-to-leading order (NLO) in
QCD, is discussed. The NLO BFKL predictions, improved by the BLM optimal scale
setting, are in good agreement with recent OPAL and L3 data at CERN LEP2. NLO
BFKL predictions for future linear colliders are presented.Comment: Latex, 7 pages, 4 figure
Orbital Angular Momentum in Scalar Diquark Model and QED
We compare the orbital angular momentum of the 'quark' in the scalar diquark
model as well as that of the electron in QED (to order {\alpha}) obtained from
the Jaffe-Manohar de- composition to that obtained from the Ji relation. We
estimate the importance of the vector potential in the definition of orbital
angular momentum
AdS/QCD and Light Front Holography: A New Approximation to QCD
The combination of Anti-de Sitter space (AdS) methods with light-front
holography leads to a semi-classical first approximation to the spectrum and
wavefunctions of meson and baryon light-quark bound states. Starting from the
bound-state Hamiltonian equation of motion in QCD, we derive relativistic
light-front wave equations in terms of an invariant impact variable zeta which
measures the separation of the quark and gluonic constituents within the hadron
at equal light-front time. These equations of motion in physical space-time are
equivalent to the equations of motion which describe the propagation of spin-J
modes in anti--de Sitter (AdS) space. Its eigenvalues give the hadronic
spectrum, and its eigenmodes represent the probability distributions of the
hadronic constituents at a given scale. Applications to the light meson and
baryon spectra are presented. The predicted meson spectrum has a string-theory
Regge form ; i.e., the square of the
eigenmass is linear in both L and n, where n counts the number of nodes of the
wavefunction in the radial variable zeta. The space-like pion and nucleon form
factors are also well reproduced. One thus obtains a remarkable connection
between the description of hadronic modes in AdS space and the Hamiltonian
formulation of QCD in physical space-time quantized on the light-front at fixed
light-front time. The model can be systematically improved by using its
complete orthonormal solutions to diagonalize the full QCD light-front
Hamiltonian or by applying the Lippmann-Schwinger method in order to
systematically include the QCD interaction terms.Comment: Invited talk, presented by SJB at the Fifth International Conference
On Quarks and Nuclear Physics (QNP09), 21-26 Sep 2009, Beijing, China. Figure
update
B-Mesons on the Transverse Lattice
We present results from a first study of -mesons that is based on a
transverse lattice formulation of light-front QCD. The shape of the Isgur-Wise
form factor is in very good agreement with experimental data. However, the
calculations yield rather large values for and compared
to contemporary calculations based on other techniques.Comment: invited talk given at CSSM workshop on `Lattice Hadron Physics',
Cairns, July 2001 and at ECT* workshop on `Light-cone Physics: Particles and
String', Trento, Sept. 200
The Two Roads to "Intrinsic Charm" in B Decays
We describe two complementary ways to show the presence of higher order
effects in the 1/m_Q expansion for inclusive B decays that have been dubbed
"Intrinsic Charm". Apart from the lessons they can teach us about QCD's
nonperturbative dynamics their consideration is relevant for precise
extractions of |V_{cb}|: for they complement the estimate of the potential
impact of 1/m_Q^4 contributions. We draw semiquantitative conclusions for the
expected scale of Weak Annihilation in semileptonic B decays, both for its
valence and non-valence components.Comment: 17 pages, 3 figure
The running coupling method with next-to-leading order accuracy and pion, kaon elm form factors
The pion and kaon electromagnetic form factors are calculated at
the leading order of pQCD using the running coupling constant method. In
calculations the leading and next-to-leading order terms in
expansion in terms of are taken into
account. The resummed expression for is found. Results of numerical
calculations for the pion (asymptotic distribution amplitude) are presented.Comment: 9 pages, 1 figur
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