24 research outputs found
Inclusive and Exclusive Scatterings from Tensor Polarized Deuteron
The possibility of using a tensor polarized deuteron target in
electroproduction reactions creates new opportunities for studying different
phenomena related to the short-range hadronic and nuclear physics. The use of
tensor polarized deuteron allows to isolate smaller than average inter-nucleon
distances for the bound two-nucleon system. In this report we consider several
of high reactions which are particularly sensitive to the short-range
two-nucleon configurations in the deuteron. The one is the relativistic
dynamics of electron-bound-nucleon scattering which can be studied in both
inclusive and exclusive reactions, other is the strong final state interaction
in close proximity of two nucleons that can be used as a sensitive probe for
color-transparency phenomena.Comment: 8 pages and 6 figures, proceedings of the Tensor Polarized Solid
Target Workshop March 10-12, 2014 (Jefferson Lab, Newport News, USA
QCD and QED dynamics of the EMC effect
Applying exact QCD sum rules for the baryon charge and energy-momentum we
demonstrate that if nucleons are the only degrees of freedom of nuclear wave
function, the structure function of a nucleus would be the additive sum of the
nucleon distributions at the same Bjorken x = AQ^2/2(p_Aq)< 0.5 up to very
small Fermi motion corrections if x>0.05. Thus the difference of the EMC ratio
from one reveals the presence of non-nucleonic degrees of freedom in nuclei.
Using exact QCD sum rules we show that the ratio R_A(x_p,Q^2) used in
experimental studies, where x_p = Q^2/2q_0 m_p deviates from one even if a
nucleus consists of nucleons with small momenta only. Use of the Bjorken x
leads to additional decrease of R_A(x,Q^2) as compared to the x_p plots.
Coherent contribution of equivalent photons into photon component of parton
wave function of a nucleus unambiguously follows from Lorentz transformation of
the rest frame nucleus Coulomb field. For A~200 photons carry ~0.0065 fraction
of the light momentum of nucleus almost compensates the difference between data
analysis in terms of Bjorken x and x_p. Different role of higher twist effects
for Q^2 probed at electron and muon beams is emphasized. Direct observations of
large and predominantly nucleonic short-range correlations in nuclei pose a
serious challenge for most of the models of the EMC effect for x>0.6. The data
are consistent with a scenario in which the hadronic EMC effect reflects
fluctuations of inter nucleon interaction due to fluctuations of color
distribution in the interacting nucleons. The dynamic realization of this
scenario is the model in which the 3q (3qg) configurations with x > 0.5 parton
have a weaker interaction with nearby nucleons, leading to suppression of such
configurations giving a right magnitude of the EMC effect. The directions for
the future studies and challenging questions are outlined.Comment: The sign in the relation of x_Bj and x_p is corrected and the
following discussion is adjusted accordingly. Discussion of the higher twist
effects is adde
Towards observation of three-nucleon short-range correlations in high Q^2 A(e, e')X reactions
We discuss the kinematical and dynamical conditions necessary for probing
highly elusive three-nucleon short range correlations~(3N-SRCs) in nuclei
through inclusive electron scattering. The kinematic requirements that should
be satisfied in order to isolate 3N-SRCs in inclusive processes are derived. We
demonstrate that the sequence of two short-range NN interactions represents the
main mechanism. Within this mechanism we predict a quadratic dependence of the
inclusive cross section ratios of nuclei to He in the 3N-SRC region to the
same ratio measured in 2N-SRC domain. The first analysis of the available data
satisfying the necessary 3N-SRC kinematical conditions is presented. This
analysis provides tantalizing signatures of scaling associated with the onset
of 3N-SRCs. The same data are also consistent with the prediction of the
quadratic relation between the ratios measured in the 3N and 2N-SRC regions for
nuclei ranging . This agreement made it possible to extract
, the probability of 3N-SRCs relative to the He nucleus. For
we obtain noticeably larger magnitudes than for the analogous
parameter, for 2N-SRCs.Comment: 31 pages and 17 figure
Hard Rescattering in QCD and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two nucleons with
high relative momentum. We sum the relevant quark rescattering diagrams, to
show that the scattering amplitude depends on a convolution between the large
angle scattering amplitude, the hard photon-quark interaction vertex and
the low-momentum deuteron wave function. The computed cross sections are in
reasonable agreement with the data.Comment: Four pages Latex, uses espcrc1.sty. Presented at 15th International
Conference on Particle and Nuclei (PANIC 99), Uppsala, Sweden, 10-16 Jun 199
QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two final-state
nucleons with high relative momentum. We sum the relevant quark rescattering
diagrams, to show that the scattering amplitude depends on a convolution
between the large angle scattering amplitude, the hard photon-quark
interaction vertex and the low-momentum deuteron wave function. The computed
absolute values of the cross section are in reasonable agreement with the data.Comment: 4 pages, revised version to be published in Phys. Rev. Let
Probing superfast quarks in nuclei through dijet production at the LHC
We investigate dijet production from proton-nucleus collisions at the Large
Hadron Collider (LHC) as a means for observing superfast quarks in nuclei with
Bjorken . Kinematically, superfast quarks can be identified through
directly measurable jet kinematics. Dynamically, their description requires
understanding several elusive properties of nuclear QCD, such as nuclear forces
at very short distances, as well as medium modification of parton distributions
in nuclei. In the present work, we develop a model for nuclear parton
distributions at large in which the nuclear dynamics at short distance
scales are described by two- and three-nucleon short range correlations (SRCs).
Nuclear modifications are accounted for using the color screening model, and an
improved description of the EMC effect is reached by using a structure function
parametrization that includes higher-twist contributions. We apply QCD
evolution at the leading order to obtain nuclear parton distributions in the
kinematic regime of the LHC, and based on the obtained distributions calculate
the cross section for dijet production. We find not only that superfast quarks
can be observed at the LHC, but also that they provide sensitivity to the
practically unexplored three-nucleon SRCs in nuclei. Additionally, the LHC can
extend our knowledge of the EMC effect to large where higher-twist
effects are negligible.Comment: 44 pages, 17 figures, final version to be published in EJP
Diffractive Heavy Quarkonium Photo- and Electroproduction in QCD
Hard diffractive photo- and electroproduction of heavy vector mesons
( and ) is evaluated within the leading approximation of QCD. In difference from our earlier
work on that subject, also the production of transversely polarized vector
mesons is calculated. Special emphasis is placed on the role of the vector
meson's light-cone wave function. In that context, conventional
non-relativistic quarkonium models and a light-front QCD bound state
calculation are critically examined and confronted with QCD expectations. Our
numerical analysis finds a significant high momentum tail in the latter wave
functions and a deviation from the expected asymptotic behavior of
. We then design an interpolation to match the
quarkonium models at large inter-quark separations with QCD expectations at
small distances. We use these results to compare our predictions for the
forward differential cross section of photo- and electroproduction
with recent experimental results from HERA. In addition, our earlier discussion
of electroproduction is updated in light of recent experimental and
theoretical enhancements.Comment: 44 pages, LaTeX, 14 figures included using epsf.tex; Final version to
appear in Phys. Rev.
Hard exclusive electroproduction of pseudoscalar mesons and QCD axial anomaly
The hard exclusive electroproduction of mesons by the longitudinal photons is considered. We calculate the ratios of the yields for the electroproduction processes off nucleons and deuterons based on the QCD factorization theorem, the low energy QCD chiral dynamics, and the QCD anomaly. Thus investigation of these ratios gives a new way to probe the physics of the spontaneous chiral symmetry breaking