11,397 research outputs found
Exclusive diffractive electroproduction of dijets in collinear factorization
Exclusive electroproduction of hard dijets can be described within the
collinear factorization. This process has clear experimental signature and
provides one with an interesting alternative venue to test QCD description of
hard diffractive processes and extract information on generalized nucleon
parton distributions. In this work we present detailed leading-order QCD
calculations of the relevant cross sections, including longitudinal momentum
fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st
Heavy-to-light form factors in the quark model with heavy propagators
We calculate the heavy-to-light form factors in the relativistic quark model
with heavy infrapropagators. Their q^2-dependence in the physical region is
defined by two parameters: the "infrared" parameter \nu characterizing the
infrared behavior of the heavy quark and the mass difference of the heavy meson
and heavy quark E=m_H-M_Q. It is found that the values of the D\to K(K^*) and
D\to \pi(\rho) form factors at q^2=0 are in excellent agreement with the
available experimental data and other approaches whereas these values for B\to
\pi(\rho) transitions are found to be larger than those of several other
models. The obtained form factors are used to calculate the widths of the
semileptonic decays of B and D mesons. The comparison of our results with the
available experimental data and other approaches is givenComment: 15 pages, 3 eps figures. New references are added, corrected some
typos. To appear in Few-Body System
Electroproduction of Soft Pions at Large Momentum Transfers
We consider pion electroproduction on a proton target close to threshold for
Q^2 in the region 1-10 GeV^2. The momentum transfer dependence of the S-wave
multipoles at threshold, E_{0+} and L_{0+}, is calculated using light-cone sum
rules.Comment: 8 pages, 3 figures; Invited talk at the workshop on Exclusive
Reactions at High Momentum Transfer, 21-24 May 2007, Newport News, Virginia,
U.S.A. and International Conference on hadron Physics TROIA'07, 30 Aug. - 3
Sept. 2007, Canakkale, Turke
Diffractive jets production in pp-collisions
We consider the exclusive diffractive dissociation of a proton into three
jets with large transverse momenta in the double-logarithmic approximation of
perturbative QCD. This process is sensitive to the proton unintegrated gluon
distribution at small x and to the proton light-cone distribution amplitudes.
According to our estimates, an observation of such processes in the early runs
at LHC is feasible for jet transverse momenta of the order of 5 GeV.Comment: Presented at International Workshop on Diffraction in High-Energy
Physics, La Londe-les-Maures, France, September 9 - 14, 200
Multiple Ionization Bursts in Laser-Driven Hydrogen Molecular Ion
Theoretical study on H in an intense infrared laser field on the
attosecond time-scale reveals that the molecular ion shows multiple bursts of
ionization within a half-cycle of the laser field oscillation, in contrast to
the widely accepted tunnel ionization picture for an atom. These bursts are
found to be induced by transient localization of the electron at one of the
nuclei, and a relation between the time instants of the localization and the
vector potential of the laser light is derived. Furthermore, an experimental
scheme is proposed to probe the localization dynamics by an extreme ultraviolet
laser pulse.Comment: 5 pages, 4 figure
Towards the theory of coherent hard dijet production on hadrons and nuclei
We carry out a detailed calculation of the cross section of pion diffraction
dissociation into two jets with large transverse momenta, originating from a
hard gluon exchange between the pion constituents. Both the quark and the gluon
contribution are considered and in the latter case we present calculations both
in covariant and in axial gauges. We find that the standard collinear
factorization does not hold in this reaction. The structure of non-factorizable
contributions is discussed and the results are compared with the experimental
data. Our conclusion is that the existing theoretical uncertainties do not
allow, for the time being, for a quantitative extraction of the pion
distribution amplitude.Comment: 45 pages, latex, 17 figures, final version to appear in Nuclear
Physics
Group expansions for impurities in superconductors
A new method is proposed for practical calculation of the effective
interaction between impurity scatterers in superconductors, based on algebraic
properties of related Nambu matrices for Green functions. In particular, we
show that the density of states within the s-wave gap can have a non-zero
contribution (impossible either in Born and in T-matrix approximation) from
non-magnetic impurities with concentration , beginning from order.Comment: 5 pages, 1 figur
Leptonic and semileptonic decays of heavy mesons
A heavy-quark limit of the Dyson-Schwinger equations is introduced and used
in an exploratory study of leptonic and semileptonic decays of heavy mesons.
The application of this framework to heavy-to-light semileptonic decays, which
require a good knowledge of light-quark propagation characteristics and
light-meson bound state amplitudes, is illustrated.Comment: 4 pages, 2 figures, Contribution to the IVth International Workshop
on Progress in Heavy Quark Physics, 20-22 Sept. 1997, Rostoc
- …