7,069 research outputs found
The general behavior of unintegrated parton distributions based on the single-scale evolution and the angular ordering constraint
To overcome the complexity of generalized two hard scale (,)
evolution equation, well known as the , , and
() evolution equations, and calculate the unintegrated parton
distribution functions (), , and ()
proposed a procedure based on () the inclusion of single-scale () only
at the last step of evolution and () the angular ordering constraint
() on the terms (the collinear approximation), to bring
the second scale, into the evolution equations. In this work we
intend to use the (Martin et al) parton distribution functions
(PDF) and try to calculate for various values of (the longitudinal
fraction of parton momentum), (the probe scale) and (the parton
transverse momentum) to see the general behavior of three dimensional at
the level up to the working energy scales (. It is shown
that there exits some pronounced peaks for the three dimensional
with respect to the two variables and at various
energies (). These peaks get larger and move to larger values of , as
the energy () is increased. We hope these peaks could be detected in the
experiments at and other laboratories in the less exclusive
processes
Semi-leptonic Decays of Heavy Quarks in Dijet Photoproduction at HERA
The production of heavy quarks has been studied in photoproduction processes
with the ZEUS detector at HERA using an integrated luminosity of . Events with a photon virtuality, , were selected with
two jets of high transverse energy and an electron in the final state.
Consideration of the distribution in - the momentum of the electron
transverse to the axis of the jet to which the electron is closest - allows a
measurement of the beauty cross-section in a restricted region of phase space.Comment: 3 pages, 3 figures. To appear in DIS99 conference proceeding
Constrained MC for QCD evolution with rapidity ordering and minimum kT
With the imminent start of LHC experiments, development of phenomenological
tools, and in particular the Monte Carlo programs and algorithms, becomes
urgent. A new algorithm for the generation of a parton shower initiated by the
single initial hadron beam is presented. The new algorithm is of the class of
the so called ``constrained MC'' type algorithm (an alternative to the backward
evolution MC algorithm), in which the energy and the type of the parton at the
end of the parton shower are constrained (predefined). The complete kinematics
configurations with explicitly constructed four momenta are generated and
tested. Evolution time is identical with rapidity and minimum transverse
momentum is used as an infrared cut-off. All terms of the leading-logarithmic
approximation in the DGLAP evolution are properly accounted for. In addition,
the essential improvements towards the so-called CCFM/BFKL models are also
properly implemented. The resulting parton distributions are cross-checked up
to the 0.1% precision level with the help of a multitude of comparisons with
other MC and non-MC programs. We regard these tests as an important asset to be
exploited at the time when the presented MC will enter as a building block in a
larger MC program for W/Z production process at LHC.Comment: Submitted to Computer Physics Communication
Moduli Spaces of Curves with Homology Chains and c=1 Matrix Models
We show that introducing a periodic time coordinate in the models of
Penner-Kontsevich type generalizes the corresponding constructions to the case
of the moduli space of curves with homology chains
\gamma\in H_1(C,\zet_k). We make a minimal extension of the resulting models
by adding a kinetic term, and we get a new matrix model which realizes a simple
dynamics of \zet_k-chains on surfaces. This gives a representation of
matter coupled to two-dimensional quantum gravity with the target space being a
circle of finite radius, as studied by Gross and Klebanov.Comment: IFUM 459/FT (LaTeX, 9 pages; a few misprints have been corrected and
the introduction has been slightly modified
A unified evaluation of iterative projection algorithms for phase retrieval
Iterative projection algorithms are successfully being used as a substitute
of lenses to recombine, numerically rather than optically, light scattered by
illuminated objects. Images obtained computationally allow aberration-free
diffraction-limited imaging and the possibility of using radiation for which no
lenses exist. The challenge of this imaging technique is transfered from the
lenses to the algorithms. We evaluate these new computational ``instruments''
developed for the phase retrieval problem, and discuss acceleration strategies.Comment: 12 pages, 9 figures, revte
Holographic Methods as Local Probes of the Atomic Order in Solids
In the last fifteen years several techniques based on the holographic
principle have been developed for the study of the 3D local order in solids.
These methods use various particles: electrons, hard x-ray photons, gamma
photons, or neutrons to image the atoms. Although the practical realisation of
the various imaging experiments is very different, there is a common thread;
the use of inside reference points for holographic imaging. In this paper we
outline the basics of atomic resolution holography using inside reference
points, especially concentrating to the hard x-ray case. Further, we outline
the experimental requirements and what has been practically realized in the
last decade. At last we give examples of applications and future perspectives.Comment: 14 pages, 6 figure
Holographic analysis of diffraction structure factors
We combine the theory of inside-source/inside-detector x-ray fluorescence
holography and Kossel lines/x ray standing waves in kinematic approximation to
directly obtain the phases of the diffraction structure factors. The influence
of Kossel lines and standing waves on holography is also discussed. We obtain
partial phase determination from experimental data obtaining the sign of the
real part of the structure factor for several reciprocal lattice vectors of a
vanadium crystal.Comment: 4 pages, 3 figures, submitte
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