12,792 research outputs found
Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector
We present a physically motivated parameterization of the chiral-odd
generalized parton distributions. The parametrization is an extension of our
previous one in the chiral-even sector which was based on the reggeized diquark
model. While for chiral even generalized distributions a quantitative fit with
uncertainty estimation can be performed using deep inelastic scattering data,
nucleon electromagnetic, axial and pseudoscalar form factors measurements, and
all available deeply virtual Compton scattering data, the chiral-odd sector is
far less constrained. While awaiting the analysis of measurements on
pseudoscalar mesons exclusive electroproduction which are key for the
extraction of chiral odd GPDs, we worked out a connection between the
chiral-even and chiral-odd reduced helicity amplitudes using Parity
transformations. The connection works for a class of models including
two-components models. This relation allows us to estimate the size of the
various chiral odd contributions and it opens the way for future quantitative
fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.
A phenomenological analysis of azimuthal asymmetries in unpolarized semi-inclusive deep inelastic scattering
We present a phenomenological analysis of the cos-phi and cos-2phi
asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on
the recent multidimensional data released by the COMPASS and HERMES
Collaborations. In the TMD framework, valid at relatively low transverse
momenta, these asymmetries arise from intrinsic transverse momentum and
transverse spin effects, and from their correlations. The role of the Cahn and
Boer-Mulders effects in both azimuthal moments is explored up to order 1/Q. As
the kinematics of the present experiments is dominated by the low-Q^2 region,
higher-twist contributions turn out to be important, affecting the results of
our fits.Comment: 18 pages, 5 figures, one paragraph added at the end of Section IV,
one reference added. PRD versio
A study on the interplay between perturbative QCD and CSS/TMD formalism in SIDIS processes
We study the Semi-Inclusive Deep Inelastic Scattering (SIDIS) cross section
as a function of the transverse momentum, . In order to describe it over a
wide region of , soft gluon resummation has to be performed. Here we will
use the original Collins-Soper-Sterman (CSS) formalism; however, the same
procedure would hold within the improved Transverse Momentum Dependent (TMD)
framework. We study the matching between the region where fixed order
perturbative QCD can successfully be applied and the region where soft gluon
resummation is necessary. We find that the commonly used prescription of
matching through the so-called Y-factor cannot be applied in the SIDIS
kinematical configurations we examine. In particular, the non-perturbative
component of the resummed cross section turns out to play a crucial role and
should not be overlooked even at relatively high energies. Moreover, the
perturbative expansion of the resummed cross section in the matching region is
not as reliable as it is usually believed and its treatment requires special
attention.Comment: Two references and an appendix added, 22 pages, 11 figure
Collins functions for pions from SIDIS and new e+e- data: a first glance at their transverse momentum dependence
New data from Belle and BaBar Collaborations on azimuthal asymmetries,
measured in e+e- annihilations into pion pairs at Q^2=112 GeV^2, allow to take
the first, direct glance at the transverse momentum dependence of the Collins
functions, in addition to their z dependence. These data, together with
available Semi-Inclusive Deep Inelastic Scattering (SIDIS) data on the Collins
asymmetry, are simultaneously analysed in the framework of the generalised
parton model assuming two alternative Q^2 evolution schemes and exploiting two
different parameterisations for the Collins functions. The corresponding
results for the transversity distributions are presented. Analogous data, newly
released by the BESIII Collaboration, on e+e- annihilations into pion pairs at
the lower Q^2 of 13 GeV^2, offer the possibility to explore the sensitivity of
these azimuthal correlations on transverse momentum dependent evolution
effects.Comment: 20 pages, 15 figures, 4 table
Transverse spin in exclusive experiments
We analyze a number of open questions in the application of the concept of generalized parton distribution to various high-energy exclusive processes. In particular we discuss the feasibility of global fits of the exclusive data, and provide a recursive procedure based on a physically motivated parametrization. By fixing the parameters to the Deeply Virtual Compton Scattering data we make predictions
for chiral odd quantities, including transversity. All of our predictions include theoretical error
GPDs, their relationships with TMDs and related topics
Generalized Parton Distributions in the chiral odd sector are evaluated by examining their contribution to the quark proton helicity amplitudes, and by using Parity transformations to establish relations with the chiral even sector. The relations we find are valid in a spectator model where the recoiling system has total spin S=0,1. These relations allow us to fix the parameters for the chiral odd generalized parton distributions using results from a global analysis of unpolarized and longitudinally polarized experimental data in the kinematical region of intermediate Bjorken x and for Q2 in the multi-GeV region. Quantitative relations between chiral odd generalized parton distributions and transverse momentum dependent
distributions are given, and their extension beyond spectator models is discussed. Contributions to the Generalized Transverse Momentum Distributions are obtained
and considered in relation to observables. The related question about recoiling baryon polarizations is discussed
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