123 research outputs found
QCD description of backward vector meson hard electroproduction
We consider backward vector meson exclusive electroproduction off nucleons in
the framework of collinear QCD factorization. Nucleon to vector meson
transition distribution amplitudes arise as building blocks for the
corresponding factorized amplitudes. In the near-backward kinematics, the
suggested factorization mechanism results in the dominance of the transverse
cross section of vector meson production () and in the
characteristic -scaling behavior of the cross section. We evaluate
nucleon to vector meson TDAs in the cross-channel nucleon exchange model and
present estimates of the differential cross section for backward ,
and meson production off protons. The resulting cross sections
are shown to be measurable in the forthcoming JLab@12 GeV experiments.Comment: 37 pages, 8 figures, 1 tabl
Renormalization programme for effective theories
We summarize our latest developments in perturbative treating the effective
theories of strong interactions. We discuss the principles of constructing the
mathematically correct expressions for the S-matrix elements at a given loop
order and briefly review the renormalization procedure. This talk shall provide
the philosophical basement as well as serve as an introduction for the material
presented at this conference by A. Vereshagin and K. Semenov-Tian-Shansky.Comment: 6 pages, talk given at HSQCD 2004, Russia, May 2004, to be published
in Proceeding
Nucleon-to-pion transition distribution amplitudes and backward electroproduction of pions
Baryon to meson transition distribution amplitudes (TDAs), non-diagonal
matrix elements of the nonlocal three quark operator between a nucleon and a
meson state, extend the concept of generalized parton distributions. These
non-perturbative objects which encode the information on three quark
correlations inside the nucleon may be accessed experimentally in backward
meson electroproduction reactions. We suggest a general framework for modelling
nucleon to pion (pi N) TDAs employing the spectral representation for pi N TDAs
in terms of quadruple distributions. The factorized Ansatz for quadruple
distributions with input from the soft-pion theorem for pi N TDAs is proposed.
It is to be complemented with a D-term like contribution from the nucleon
exchange in the cross channel.
We present our estimates of the unpolarized cross section and of the
transverse target single spin asymmetry for backward pion electroproduction
within the QCD collinear factorization approach in which the non-perturbative
part of the amplitude involves pi N TDAs. The cross section is sizable enough
to be studied in high luminosity experiments such as J-lab@12GeV and EIC.Comment: proceedings of QNP 2012, Sixth International Conference on Quarks and
Nuclear Physics, April 16-20, 2012, Ecole Polytechnique, Palaiseau, Franc
Exploring the nucleon structure through GPDs and TDAs in hard exclusive processes
Generalized Parton Distributions (GPDs) offer a new way to access the quark
and gluon nucleon structure. We review recent progress in this domain,
emphasizing the need to supplement the experimental study of deeply virtual
Compton scattering by its crossed version, timelike Compton scattering. We also
describe the extension of the GPD concept to three quark operators and the
relevance of their nucleon to meson matrix elements, namely the transition
distribution amplitudes (TDAs) which factorize in backward meson
electroproduction and related processes. We discuss the main properties of the
TDAs. \Comment: 8 pages; to be published in the proceedings of the conference "PHOTON
2011, International Conference on the Structure and the Interactions of the
Photon ", Spa, Belgium, 22-27 Mai 201
Crossed channel analysis of quark and gluon generalized parton distributions with helicity flip
Quark and gluon helicity flip generalized parton distributions (GPDs) address
the transversity quark and gluon structure of the nucleon. In order to
construct a theoretically consistent parametrization of these hadronic matrix
elements, we work out the set of combinations of those GPDs suitable for the
partial wave (PW) expansion in the cross-channel. This universal
result will help to build up a flexible parametrization of these important
hadronic non-perturbative quantities, using for instance the approaches based
on the conformal PW expansion of GPDs such as the Mellin-Barnes integral or the
dual parametrization techniques.Comment: 34 pages, 1 figure, 4 table
Toward modelization of quark and gluon transversity generalized parton distributions
Quark and gluon helicity flip generalized parton distributions (GPDs) encode
the information on the nucleon structure in the transversity sector. In order
to build a theoretically consistent phenomenological parametrization for these
hadronic matrix element within the framework of the dual parametrization of
GPDs (or with the equivalent approach of the SO(3) partial waves (PW) expansion
with the Mellin-Barnes integral techniques) we establish the set of
combinations of parton helicity flip GPDs suitable for the expansion in the
cross channel SO(3) PWs.Comment: 6 pages, DIS 2014, XXII. International Workshop on Deep-Inelastic
Scattering and Related Subjects, 28 April - 2 May 2014, Warsaw, Polan
New results in exclusive hard reactions
Generalized Parton Distributions offer a new way to access the quark and
gluon nucleon structure. We review recent progress in this domain, emphasizing
the need to supplement the experimental study of DVCS by its crossed version,
timelike Compton scattering (TCS), where data at high energy should appear
thanks to the study of ultraperipheral collisions at the LHC. This will open
the access to very low skewness quark and gluon GPDs. Our leading order
estimates show that the factorization scale dependence of the amplitudes is
quite high. This fact demands the understanding of higher order contributions
with the hope that they will stabilize this scale dependence. The magnitudes of
the NLO coefficient functions are not small and neither is the difference of
the coefficient functions appearing respectively in the DVCS and TCS
amplitudes. The conclusion is that extracting the universal GPDs from both TCS
and DVCS reactions requires much care. We also describe the extension of the
GPD concept to three quark operators and the relevance of their nucleon to
meson matrix elements, namely the transition distribution amplitudes (TDAs)
which factorize in hard exclusive pion electroproduction off a nucleon in the
backward region and baryon-antibaryon annihilation into a pion and a lepton
pair. We discuss the main properties of the TDAs.Comment: 4 pages, to be published in the proceedings of the 2011 Europhysics
Conference on High Energy Physics-HEP 2011, July 21-27, 2011, Grenoble,
Rhone-Alpes, Franc
Bootstrap and the physical values of resonance parameters
This is the 6th paper in the series developing the formalism to manage the
effective scattering theory of strong interactions. Relying on the theoretical
scheme suggested in our previous publications we concentrate here on the
practical aspect and apply our technique to the elastic pion-nucleon scattering
amplitude. We test numerically the pion-nucleon spectrum sum rules that follow
from the tree level bootstrap constraints. We show how these constraints can be
used to estimate the tensor and vector coupling constants. At last, we
demonstrate that the tree-level low energy expansion coefficients computed in
the framework of our approach show nice agreement with known experimental data.
These results allow us to claim that the extended perturbation scheme is quite
reasonable from the computational point of view.Comment: 41 pages, 7 figure
Differential technique for the covariant orbital angular momentum operators
The orbital angular momentum operator expansion turns to be a powerful tool
to construct the fully covariant partial wave amplitudes of hadron decay
reactions and hadron photo- and electroproduction processes. In this paper we
consider a useful development of the orbital angular momentum operator
expansion method. We present the differential technique allowing the direct
calculation of convolutions of two orbital angular momentum operators with an
arbitrary number of open Lorentz indices. This differential technique greatly
simplifies calculations when the reaction subject to the partial wave analysis
involves high spin particles in the initial and/or final states. We also
present a useful generalization of the orbital angular momentum operators.Comment: 14 page
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