68 research outputs found
A Numerical Estimate of the Small- Region in the BFKL Pomeron
A computer study is performed to estimate the influence of the small-
region in the BFKL evolution equation. We consider the small-x region of the
deep inelastic structure function and show that the magnitude of the
small- region depends on and . We suggest that the width of the
-distribution in the final state may serve as an additional
footprint of BFKL dynamics. For diffractive dissociation it is shown that the
contribution of the infrared region is large - even for large . This
contribution becomes smaller only if restrictions on the final state are
imposed.Comment: 15 pages, latex, 9 figures ,revised version, some discussion added,
one reference added, two figures removed, final version to be published in
Phys. Lett.
Dijet Production at Hadron--Hadron Colliders in the BFKL Approach
The production in high-energy hadron collisions of a pair of jets with large
rapidity separation is studied in an improved BFKL formalism. By recasting the
analytic solution of the BFKL equation as an explicit order-by-order sum over
emitted gluons, the effects of phase space constraints and the running coupling
are studied. Particular attention is paid to the azimuthal angle decorrelation
of the jet pair. The inclusion of sub-leading effects significantly improves
the agreement between the theoretical predictions and recent preliminary
measurements from the Dzero collaboration.Comment: 19 pages LaTeX; one figure corrected; conclusions unchange
A unified BFKL and GLAP description of data
We argue that the use of the universal unintegrated gluon distribution and
the (or high energy) factorization theorem provides the natural framework
for describing observables at small x. We introduce a coupled pair of evolution
equations for the unintegrated gluon distribution and the sea quark
distribution which incorporate both the resummed leading BFKL
contributions and the resummed leading GLAP contributions. We solve
these unified equations in the perturbative QCD domain using simple parametic
forms of the nonperturbative part of the integrated distributions. With only
two (physically motivated) input parameters we find that this
factorization approach gives an excellent description of the measurements of
at HERA. In this way the unified evolution equations allow us to
determine the gluon and sea quark distributions and, moreover, to see the x
domain where the resummed effects become significant. We use
factorization to predict the longitudinal structure function and
the charm component of .Comment: 25 pages, LaTeX, 9 figure
Inclusive production of meson in proton-proton collisions at BNL RHIC
Inclusive cross sections for production in proton-proton collisions
were calculated in the -factorization approach for the RHIC energy.
Several mechanisms were considered, including direct color-singlet mechanism,
radiative decays of mesons, decays of , open-charm associated
production of as well as weak decays of B mesons. Different
unintegrated gluon distributions from the literature were used. We find that
radiative decays and direct color-singlet contributions constitute the
dominant mechanism of production. These process cannot be consistently
treated within collinear-factorization approach. The results are compared with
recent RHIC data. The new precise data at small transverse momenta impose
stringent constraints on UGDFs. Some UGDFs are inconsistent with the new data.
The Kwieci\'nski UGDFs give the best description of the data. In order to
verify the mechanism suggested here we propose -- jet correlation
measurement and an independent measurement of meson production in
and/or decay channels. Finally, we address the issue of
\J spin alignment.Comment: 26 pages, 20 figures, the text was slightly modified, the title was
modified, more discussion was added, one figure was removed, one was adde
Dijet correlations at RHIC, leading-order -factorization approach versus next-to-leading order collinear approach
We compare results of -factorization approach and next-to-leading order
collinear-factorization approach for dijet correlations in proton-proton
collisions at RHIC energies. We discuss correlations in azimuthal angle as well
as correlations in two-dimensional space of transverse momenta of two jets.
Some -factorization subprocesses are included for the first time in the
literature. Different unintegrated gluon/parton distributions are used in the
-factorization approach. The results depend on UGDF/UPDF used. For
collinear NLO case the situation depends significantly on whether we consider
correlations of any two jets or correlations of leading jets only. In the first
case the contributions associated with soft radiations summed up in
the -factorization approach dominate at and at equal
moduli of jet transverse momenta. The collinear NLO contributions
dominate over -factorization cross section at small relative azimuthal
angles as well as for asymmetric transverse momentum configurations. In the
second case the NLO contributions vanish at small relative azimuthal angles
and/or large jet transverse-momentum disbalance due to simple kinematical
constraints. There are no such limitations for the -factorization
approach. All this makes the two approaches rather complementary. The role of
several cuts is discussed and quantified.Comment: 26 pages, 17 figure
Spin dependent structure function g_1 at low x and low Q^2
Theoretical description of the spin dependent structure function g_1(x,Q^2)
in the region of low values of x and Q^2 is presented. It contains the Vector
Meson Dominance contribution and the QCD improved parton model suitably
extended to the low Q^2 domain. Theoretical predictions are compared with the
recent experimental data in the low x, low Q^2 region
Observable jets from the BFKL chain
We derive a modified form of the BFKL equation which enables the structure of
the gluon emissions to be studied in small deep inelastic scattering. The
equation incorporates the resummation of the virtual and unresolved real gluon
emissions. We solve the equation to calculate the number of small
deep-inelastic events containing 0,1,2 ...resolved gluon jets, that is jets
with transverse momenta . We study the jet decomposition for
different choices of the jet resolution parameter .Comment: 14 pages, Latex, 13 ps figure
Muscle pathology in myotonic dystrophy: light and electron microscopic investigation in eighteen patients
Myotonic dystrophy (DM) is the most common muscular dystrophy in adults.
Two known genetic subtypes include DM1 (myotonic dystrophy type 1) and
DM2 (myotonic dystrophy type 2). Genetic testing is considered as the only
reliable diagnostic criterion in myotonic dystrophies. Relatively little is known
about DM1 and DM2 myopathology. Thus, the aim of our study was to characterise
light and electron microscopic features of DM1 and DM2 in patients with
genetically proven types of the disease. We studied 3 DM1 cases and 15 DM2
cases from which muscle biopsies were taken for diagnostic purposes during
the period from 1973 to 2006, before genetic testing became available at our
hospital. The DM1 group included 3 males (age at biopsy 15–19). The DM2
group included 15 patients (5 men and 10 women, age at biopsy 26–60). The
preferential type 1 fibre atrophy was seen in all three DM1 cases in light microscopy,
and substantial central nucleation was present in two biopsies.
Electron microscopy revealed central nuclei in all three examined muscle biopsies.
No other structural or degenerative changes were detected, probably due to the
young age of our patients. Central nucleation, prevalence of type 2 muscle fibres,
and the presence of pyknotic nuclear clumps were observed in DM2 patients in
light microscopy. Among the ultrastructural abnormalities observed in our DM2
group, the presence of internal nuclei, severely atrophied muscle fibres, and lipofuscin
accumulation were consistent findings. In addition, a variety of ultrastructural
abnormalities were identified by us in DM2. It appears that no single ultrastructural
abnormality is characteristic for the DM2 muscle pathology. It seems, however,
that certain constellations of morphological changes might be indicative of
certain types of myotonic dystrophy. (Folia Morphol 2011; 70, 2: 121–129
Solution of the Kwiecinski evolution equations for unintegrated parton distributions using the Mellin transform
The Kwiecinski equations for the QCD evolution of the unintegrated parton
distributions in the transverse-coordinate space (b) are analyzed with the help
of the Mellin-transform method. The equations are solved numerically in the
general case, as well as in a small-b expansion which converges fast for b
Lambda_QCD sufficiently small. We also discuss the asymptotic limit of large bQ
and show that the distributions generated by the evolution decrease with b
according to a power law. Numerical results are presented for the pion
distributions with a simple valence-like initial condition at the low scale,
following from chiral large-N_c quark models. We use two models: the Spectral
Quark Model and the Nambu--Jona-Lasinio model. Formal aspects of the equations,
such as the analytic form of the b-dependent anomalous dimensions, their
analytic structure, as well as the limits of unintegrated parton densities at x
-> 0, x -> 1, and at large b, are discussed in detail. The effect of spreading
of the transverse momentum with the increasing scale is confirmed, with
growing asymptotically as Q^2 alpha(Q^2). Approximate formulas for
for each parton species is given, which may be used in practical
applications.Comment: 18 pages, 6 figures, RevTe
Wetting of two-component drops: Marangoni contraction versus autophobing
The wetting properties of multi-component liquids are crucial to numerous
industrial applications. The mechanisms that determine the contact angles for
such liquids remain poorly understood, with many intricacies arising due to
complex physical phenomena, for example due to the presence of surfactants.
Here, we consider two-component drops that consist of mixtures of vicinal
alkane diols and water. These diols behave surfactant-like in water. However,
the contact angles of such mixtures on solid substrates are surprisingly large.
We experimentally reveal that the contact angle is determined by two separate
mechanisms of completely different nature, namely Marangoni contraction
(hydrodynamic) and autophobing (molecular). It turns out that the length of the
alkyl tail of the alkane diol determines which mechanism is dominant,
highlighting the intricate coupling between molecular physics and the
macroscopic wetting of complex fluids
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