59 research outputs found
Coherent Vector Meson Production from Deuterons
In this paper we discuss coherent photo- and leptoproduction of vector mesons
from deuterons at intermediate (virtual) photon energies, 3 < nu < 30 GeV. We
consider the scattering from unpolarized and polarized targets as well as
processes where the polarization of the recoil deuteron is measured. Our main
motivation results from the need for a quantitative analysis of the space-time
structure of photon-induced processes. In this respect we suggest several
possibilities to explore the characteristic longitudinal interaction length in
coherent vector meson production. Furthermore, we outline methods for an
investigation of color coherence effects. In addition to the presentation of
benchmark values for the maximal possible color coherence effect in various
kinematic regions, we illustrate the anticipated phenomena within the color
diffusion model. Finally we recall that the determination of vector
meson-nucleon cross sections is not a closed issue. Besides being not known to
a satisfying accuracy, they can be used to determine the strength of the
D-state in low mass vector mesons.Comment: LaTeX, 22 page
Hard breakup of the deuteron into two Delta-isobars
We study high energy photodisintegration of the deuteron into two
-isobars at large center of mass angles within the QCD hard
rescattering model (HRM). According to the HRM, the process develops in three
main steps: the photon knocks the quark from one of the nucleons in the
deuteron; the struck quark rescatters off a quark from the other nucleon
sharing the high energy of the photon; then the energetic quarks recombine into
two outgoing baryons which have large transverse momenta. Within the HRM, the
cross section is expressed through the amplitude of scattering which we evaluated based on the quark-interchange
model of hard hadronic scattering. Calculations show that the angular
distribution and the strength of the photodisintegration is mainly determined
by the properties of the
scattering. We predict that the cross section of
the deuteron breakup to is 4-5 times larger than that
of the breakup to the channel. Also, the angular
distributions for these two channels are markedly different. These can be
compared with the predictions based on the assumption that two hard
-isobars are the result of the disintegration of the preexisting
components of the deuteron wave function. In this case, one
expects the angular distributions and cross sections of the breakup in both and channels to be similar.Comment: 17 pages, 3 figure
Coherent Vector Meson Photo-Production from Deuterium at Intermediate Energies
We analyze the cross section for vector meson photo-production off a deuteron
for the intermediate range of photon energies starting at a few GeVs above the
threshold and higher. We reproduce the steps in the derivation of the
conventional non-relativistic Glauber expression based on an effective
diagrammatic method while making corrections for Fermi motion and intermediate
energy kinematic effects. We show that, for intermediate energy vector meson
production, the usual Glauber factorization breaks down and we derive
corrections to the usual Glauber method to linear order in longitudinal nucleon
momentum. The purpose of our analysis is to establish methods for probing
interesting physics in the production mechanism for phi-mesons and heavier
vector mesons. We demonstrate how neglecting the breakdown of Glauber
factorization can lead to errors in measurements of basic cross sections
extracted from nuclear data.Comment: 41 pages, 13 figures, figure 9 is compressed from previous version,
typos fixe
Hard probes of short-range nucleon-nucleon correlations
One of the primary goals of nuclear physics is providing a complete
description of the structure of atomic nuclei. While mean-field calculations
provide detailed information on the nuclear shell structure for a wide range of
nuclei, they do not capture the complete structure of nuclei, in particular the
impact of small, dense structures in nuclei. The strong, short-range component
of the nucleon-nucleon potential yields hard interactions between nucleons
which are close together, generating a high-momentum tail to the nucleon
momentum distribution, with momenta well in excess of the Fermi momentum. This
high-momentum component of the nuclear wave-function is one of the most poorly
understood parts of nuclear structure.
Utilizing high-energy probes, we can isolate scattering from high-momentum
nucleons, and use these measurements to examine the structure and impact of
short-range nucleon-nucleon correlations. Over the last decade we have moved
from looking for evidence of such short-range structures to mapping out their
strength in nuclei and examining their isospin structure. This has been made
possible by high-luminosity and high-energy accelerators, coupled with an
improved understanding of the reaction mechanism issues involved in studying
these structures. We review the general issues related to short-range
correlations, survey recent experiments aimed at probing these short-range
structures, and lay out future possibilities to further these studies.Comment: Review article to appear in Prog.Part.Nucl.Phys. 77 pages, 33 figure
Hadrons in the Nuclear Medium
Quantum Chromodynamics, the microscopic theory of strong interactions, has
not yet been applied to the calculation of nuclear wave functions. However, it
certainly provokes a number of specific questions and suggests the existence of
novel phenomena in nuclear physics which are not part of the the traditional
framework of the meson-nucleon description of nuclei. Many of these phenomena
are related to high nuclear densities and the role of color in nucleonic
interactions. Quantum fluctuations in the spatial separation between nucleons
may lead to local high density configurations of cold nuclear matter in nuclei,
up to four times larger than typical nuclear densities. We argue here that
experiments utilizing the higher energies available upon completion of the
Jefferson Laboratory energy upgrade will be able to probe the quark-gluon
structure of such high density configurations and therefore elucidate the
fundamental nature of nuclear matter. We review three key experimental
programs: quasi-elastic electro-disintegration of light nuclei, deep inelastic
scattering from nuclei at , and the measurement of tagged structure
functions. These interrelated programs are all aimed at the exploration of the
quark structure of high density nuclear configurations.
The study of the QCD dynamics of elementary hard processes is another
important research direction and nuclei provide a unique avenue to explore
these dynamics. We argue that the use of nuclear targets and large values of
momentum transfer at would allow us to determine whether the physics of the
nucleon form factors is dominated by spatially small configurations of three
quarks.Comment: 52 pages IOP style LaTex file and 20 eps figure
Hard Photodisintegration of a Proton Pair
We present a study of high energy photodisintegration of proton-pairs through
the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used
in kinematics corresponding to a proton pair with high relative momentum and a
neutron nearly at rest. The s-11 scaling of the cross section, as predicted by
the constituent counting rule for two nucleon photodisintegration, was observed
for the first time. The onset of the scaling is at a higher energy and the
cross section is significantly lower than for deuteron (pn pair)
photodisintegration. For photon energies below the scaling region, the scaled
cross section was found to present a strong energy-dependent structure not
observed in deuteron photodisintegration.Comment: 7 pages, 3 figures, for submission to Phys. Lett.
Recent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars
Novel processes probing the decay of nucleus after removal of a nucleon with
momentum larger than Fermi momentum by hard probes finally proved unambiguously
the evidence for long sought presence of short-range correlations (SRCs) in
nuclei. In combination with the analysis of large , A(e,e')X processes at
they allow us to conclude that (i) practically all nucleons with momenta
300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii)
probability of such SRCs in medium and heavy nuclei is , iii) a fast
removal of such nucleon practically always leads to emission of correlated
nucleon with approximately opposite momentum, iv) proton removal from
two-nucleon SRCs in 90% of cases is accompanied by a removal of a neutron and
only in 10% by a removal of another proton. We explain that observed absolute
probabilities and the isospin structure of two nucleon SRCs confirm the
important role that tensor forces play in internucleon interactions. We find
also that the presence of SRCs requires modifications of the Landau Fermi
liquid approach to highly asymmetric nuclear matter and leads to a
significantly faster cooling of cold neutron stars with neutrino cooling
operational even for . The effect is even stronger for the
hyperon stars. Theoretical challenges raised by the discovered dominance of
nucleon degrees of freedom in SRCs and important role of the spontaneously
broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are
considered. We also outline directions for future theoretical and experimental
studies of the physics relevant for SRCs.Comment: 74 pages. Review article, updated version to be published in
International Journal of Modern Physics
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
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