247 research outputs found
The dual parameterization of the proton generalized parton distribution functions H and E and description of the DVCS cross sections and asymmetries
We develop the minimal model of a new leading order parameterization of GPDs
introduced by Shuvaev and Polyakov. The model for GPDs H and E is formulated in
terms of the forward quark distributions, the Gegenbauer moments of the D-term
and the forward limit of the GPD E. The model is designed primarely for small
and medium-size values of x_B, x_B \leq 0.2.
We examined two different models of the t-dependence of the GPDs: The
factorized exponential model and the non-factorized Regge-motivated model.
Using our model, we successfully described the DVCS cross section measured by
H1 and ZEUS, the moments of the beam-spin A_{LU}^{\sin \phi}, beam-charge
A_{C}^{\cos \phi} and transversely-polarized target A_{UT}^{\sin \phi \cos
\phi} DVCS asymmetries measured by HERMES and A_{LU}^{\sin \phi} measured by
CLAS. The data on A_{C}^{\cos \phi} prefers the Regge-motivated model of the
t-dependence of the GPDs. The data on A_{UT}^{\sin \phi \cos \phi} indicates
that the u and d quarks carry only a small fraction of the proton total angular
momentum.Comment: 33 pages, 11 figure
Polarized light ions and spectator nucleon tagging at EIC
An Electron-Ion Collider (EIC) with suitable forward detection capabilities
would enable a unique experimental program of deep-inelastic scattering (DIS)
from polarized light nuclei (deuterium 2H, helium 3He) with spectator nucleon
tagging. Such measurements promise significant advances in several key areas of
nuclear physics and QCD: (a) neutron spin structure, by using polarized
deuterium and eliminating nuclear effects through on-shell extrapolation in the
spectator proton momentum; (b) quark/gluon structure of the bound nucleon at x
> 0.1 and the dynamical mechanisms acting on it, by measuring the spectator
momentum dependence of nuclear structure functions; (c) coherent effects in
QCD, by exploring shadowing in tagged DIS on deuterium at x << 0.1. The JLab
MEIC design (CM energy sqrt{s} = 15-50 GeV/nucleon, luminosity ~ 10^{34}
cm^{-2} s^{-1}) provides polarized deuterium beams and excellent coverage and
resolution for forward spectator tagging. We summarize the physics topics, the
detector and beam requirements for spectator tagging, and on-going R&D efforts.Comment: 6 pages, 2 figures. Prepared for proceedings of DIS 2014, XXII.
International Workshop on Deep-Inelastic Scattering and Related Subjects,
University of Warsaw, Poland, April 28 - May 2, 201
Neutron spin structure with polarized deuterons and spectator proton tagging at EIC
The neutron's deep-inelastic structure functions provide essential
information for the flavor separation of the nucleon parton densities, the
nucleon spin decomposition, and precision studies of QCD phenomena in the
flavor-singlet and nonsinglet sectors. Traditional inclusive measurements on
nuclear targets are limited by dilution from scattering on protons, Fermi
motion and binding effects, final-state interactions, and nuclear shadowing at
x << 0.1. An Electron-Ion Collider (EIC) would enable next-generation
measurements of neutron structure with polarized deuteron beams and detection
of forward-moving spectator protons over a wide range of recoil momenta (0 <
p_R < several 100 MeV in the nucleus rest frame). The free neutron structure
functions could be obtained by extrapolating the measured recoil momentum
distributions to the on-shell point. The method eliminates nuclear
modifications and can be applied to polarized scattering, as well as to
semi-inclusive and exclusive final states. We review the prospects for neutron
structure measurements with spectator tagging at EIC, the status of R&D
efforts, and the accelerator and detector requirements.Comment: 11 pages, 3 figures. To appear in proceedings of Tensor Polarized
Solid Target Workshop, Jefferson Lab, March 10-12, 201
Methodological and analytical provision of region monitoring
The article reflects methodological and applied aspects of the quality and completeness of information provided to the monitoring taking into account the level of spatial aggregation.
The authors suggest an algorithm on forming informational blocks of monitoring on the region level which allows to implement the functions of the given analytical tool.
Furthermore, the article provides the reasons for integrating information within the united methodological and legal area of Russian public statistics in order to form the representative database for regional monitoring and analysis.peer-reviewe
Simple Classification of Light Baryons
We introduce a classification number which describes the baryon mass
information in a fuzzy manner. According to and of baryons, we put
all known light baryons in a simple table in which some baryons with same (,
) are classified as members of known octets or decuplets. Meanwhile, we
predict two new possible octets.Comment: 5 latex pages, 5 tables, no figur
On the A-dependence of nuclear generalized parton distributions
We perform a microscopic evaluation of nuclear GPDs for spin-0 nuclei in the
framework of the Walecka model. We demonstrate that the meson (non-nucleon)
degrees of freedom dramatically influence nuclear GPDs, which is revealed in
the non-trivial and unexpected A-dependence of DVCS observables. In particular,
we find that the first moment of the nuclear D-term, d_A(0) ~ A^2.26, which
confirms the earlier prediction of M.Polyakov. We find that in the HERMES
kinematics, contrary to the free proton case, the nuclear meson degrees of
freedom in large nuclei enhance the nuclear DVCS amplitude which becomes
comparable to the Bethe-Heitler amplitude, and, thus, give the non-trivial
A-dependence to the DVCS asymmetries: as a function of the atomic number the
beam-charge asymmetry increases whereas the beam-spin asymmetry decreases
slowly.Comment: Final version published in J. Phys. G. 17 pages, 9 figure
Color coherent phenomena on nuclei and the QCD evolution equation
We review the phenomenon of color coherence in quantum chromodynamics (QCD),
its implications for hard and soft processes with nuclei, and its experimental
manifestations. The relation of factorization theorems in QCD with color
coherence phenomena in deep inelastic scattering (DIS) and color coherence
phenomena in hard exclusive processes is emphasized. Analyzing numerically the
QCD evolution equation for conventional and skewed parton densities in nuclei,
we study the onset of generalized color transparency and nuclear shadowing of
the sea quark and gluon distributions in nuclei as well as related phenomena.
Such novel results as the dependence of the effective coherence length on
and general trends of the QCD evolution are discussed. The limits of the
applicability of the QCD evolution equation at small Bjorken are estimated
by comparing the inelastic quark-antiquark- and two gluon-nucleon (nucleus)
cross sections, calculated within the DGLAP approximation, with the dynamical
boundaries, which follow from the unitarity of the matrix for purely QCD
interactions. We also demonstrate that principles of color coherence play an
important role in the processes of soft diffraction off nuclei.Comment: 58 pages, 19 figures, Revtex. Minor editor's changes, final version
published in J.Phys. G27 (2001) R23-6
Impact of nuclear dependence of R=\sigma_L/\sigma_T on antishadowing in nuclear structure functions
We study the impact of the nuclear dependence of R=\sigma_L/\sigma_T on the
extraction of the F_2^A/F_2^D and F_1^A/F_1^D structure function ratios from
the data on the \sigma^A/\sigma^D cross section ratios. Guided by indications
of the nuclear dependence of R from the world data, we examine selected sets of
EMC, BCDMS, NMC and SLAC data and find that F_1^A/F_1^D < \sigma^A/\sigma^D
\leq F_2^A/F_2^D. In particular, we observe that the nuclear enhancement
(antishadowing) for F_1^A/F_1^D in the interval 0.1 < x < 0.3 becomes
significantly reduced or even disappears, which indicates that antishadowing is
dominated by the longitudinal structure function F_L. We also argue that
precise measurements of nuclear modifications of R and F_L^A have the potential
to constrain the poorly known gluon distribution in nuclei over a wide range of
x.Comment: 9 pages, 8 figures, 1 tabl
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