394 research outputs found
Spin dependent structure function at small and small
Theoretical expectations concerning the low and low behaviour of
are summarized and compared with the recent SMC data.Comment: 4 pages, plain LATEX, 1 eps figure; contribution to 3rd UK
Phenomenology Workshop on HERA Physics, St. John's College, Durham, UK,
September 199
High-energy factorization and evolution with improved kinematics
The high-energy factorization and the associated B-JIMWLK or BK evolution
equations are presented, using the example of DIS structure functions. The
necessity of taking gluon saturation into account is discussed, and also the
various approximations underlying high-energy factorization. The appearance of
large NLL corrections in such a framework with or without gluon saturation is
recalled, and their physical origin is explained. Finally, old and new results
are presented about the resummation of some of those large corrections, related
to kinematical approximations.Comment: 10 pages, To appear in the proceedings of the "QCD evolution
workshop: from collinear to non collinear case", 8 - 9 Apr 201
The unintegrated gluon distribution from the CCFM equation
The gluon distribution f(x, k_t^2,mu^2), unintegrated over the transverse
momentum k_t of the gluon, satisfies the angular-ordered CCFM equation which
interlocks the dependence on the scale k_t with the scale \mu of the probe. We
show how, to leading logarithmic accuracy, the equation can be simplified to a
single scale problem. In particular we demonstrate how to determine the
two-scale unintegrated distribution f(x,k_t^2,mu^2) from knowledge of the
integrated gluon obtained from a unified scheme embodying both BFKL and DGLAP
evolution.Comment: 16 pages LaTeX, 3 eps figure
Heavy quark production as sensitive test for an improved description of high energy hadron collisions
QCD dynamics at small quark and gluon momentum fractions or large total
energy, which plays a major role for HERA, the Tevatron, RHIC and LHC physics,
is still poorly understood. For one of the simplest processes, namely
bottom-antibottom production, next-to-leading-order perturbation theory fails.
We show that the combination of two recently developed theoretical concepts,
the k_perp-factorization and the next-to-leading-logarithmic-approximation BFKL
vertex, gives perfect agreement with data. One can therefore hope that these
concepts provide a valuable foundation for the description of other high energy
processes.Comment: RevTeX, 4 pages, 7 figures titel and abstract changed, several
formulations modified in the text, 1 figure droppe
High Energy Quark-Antiquark Elastic scattering with Mesonic Exchange
We studies the high energy elastic scattering of quark anti-quark with an
exchange of a mesonic state in the channel with .
Both the normalization factor and the Regge trajectory can be calculated in
PQCD in cases of fixed (non-running) and running coupling constant. The
dependence of the Regge trajectory on the coupling constant is highly
non-linear and the trajectory is of order of in the interesting physical
range.Comment: 29 page
Precise Determination of Electroweak Parameters in Neutrino-Nucleon Scattering
A systematic error in the extraction of from nuclear deep
inelastic scattering of neutrinos and antineutrinos arises from higher-twist
effects arising from nuclear shadowing. We explain that these effects cause a
correction to the results of the recently reported significant deviation from
the Standard Model that is potentially as large as the deviation claimed, and
of a sign that cannot be determined without an extremely careful study of the
data set used to model the input parton distribution functions.Comment: 3pages, 0 figures, version to be published by IJMP
Towards a solution of the charmonium production controversy: k_t-factorization versus color octet mechanism
The cross section of \chi_{cJ} hadroproduction is calculated in the
k_t-factorization approach. We find a significant contribution of the \chi_{c1}
state due to non-applicability of the Landau-Yang theorem because of off-shell
gluons. The results are in agreement with data and, in contrast to the
collinear factorization, show a dominance of the color singlet part and a
strong suppression of the color octet contribution. Our results could therefore
lead to a solution of the longstanding controversy between the color singlet
model and the color octet mechanism.Comment: 4 pages, 5 figures, final PRL versio
Unintegrated parton distributions and inclusive jet production at HERA
We describe how unintegrated parton distributions can be calculated from
conventional integrated distributions. We extend and improve the 'last-step'
evolution approach, and explain why doubly-unintegrated parton distributions
are necessary. We generalise k_t-factorisation to (z,k_t)-factorisation. We
apply the formalism to inclusive jet production in deep-inelastic scattering,
mainly at leading-order, but we also study the extension to next-to-leading
order. We compare the predictions with recent HERA data.Comment: 32 pages, 11 figures. Version to appear in Eur. Phys. J.
Theoretical issues of small physics
The perturbative QCD predictions concerning deep inelastic scattering at low
are summarized. The theoretical framework based on the leading log
resummation and factorization theorem is described and some recent
developments concerning the BFKL equation and its generalization are discussed.
The QCD expectations concerning the small behaviour of the spin dependent
structure function are briefly summarized and the importance of
the double logarithmic terms which sum contributions containing the leading
powers of is emphasised. The role of studying final states
in deep inelastic scattering for revealing the details of the underlying
dynamics at low is pointed out and some dedicated measurements, like deep
inelastic scattering accompanied by an energetic jet, the measurement of the
transverse energy flow etc., are briefly discussed.Comment: 17 pages, LATEX, 7 uuencoded eps figures include
Non-linear evolution in CCFM: The interplay between coherence and saturation
We solve the CCFM equation numerically in the presence of a boundary
condition which effectively incorporates the non-linear dynamics. We retain the
full dependence of the unintegrated gluon distribution on the coherence scale,
and extract the saturation momentum. The resulting saturation scale is a
function of both rapidity and the coherence momentum. In Deep Inelastic
Scattering this will lead to a dependence of the saturation scale on the photon
virtuality in addition to the usual x-Bjorken dependence. At asymptotic
energies the interplay between the perturbative non-linear physics, and that of
the QCD coherence, leads to an interesting and novel dynamics where the
saturation momentum itself eventually saturates. We also investigate various
implementations of the "non-Sudakov" form factor. It is shown that the
non-linear dynamics leads to almost identical results for different form
factors. Finally, different choices of the scale of the running coupling are
analyzed and implications for the phenomenology are discussed.Comment: 37 pages, 21 figure
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