144 research outputs found
High Energy Break-Up of Few-Nucleon Systems
We discus recent developments in theory of high energy two-body break-up
reactions of few-nucleon systems. The characteristics of these reactions are
such that the hard two-body quasielastic subprocess can be clearly separated
from the accompanying soft subprocesses. We discuss in details the hard
rescattering model (HRM) in which hard photodisintegration develops in two
stages. At first, photon knocks-out an energetic quark which rescatters
subsequently with a quark of the other nucleon. The latter provides a mechanism
of sharing the initial high momentum of the photon by the outgoing two
nucleons. Within HRM we discuss hard break-up reactions involving and
targets. Another development of HRM is the prediction of new helicity
selection mechanism for hard two-body reactions, which was apparently confirmed
in the recent JLab experiment.Comment: To appear in the proceedings of Workshop on Exclusive Reactions at
High Momentum Transfer, Newport News, Virgina, 21-24 May 200
Hard Rescattering Mechanism in High Energy Photodisintegration of the Light Nuclei
We discuss the high energy photodisintegrataion of light nuclei in which the
energy of the absorbed photon is equally shared between two nucleons in the
target. For these reactions we investigate the model in which photon absorption
by a quark in one nucleon followed by its high momentum transfer interaction
with a quark of the other nucleon leads to the production of two nucleons with
high relative momentum. We sum the relevant quark rescattering diagrams, and
demonstrate that the scattering amplitude can be expressed as a convolution of
the large angle NN scattering amplitude, the hard photon-quark interaction
vertex and the low-momentum nuclear wave function. Within this model we
calculate the cross sections and polarization observables of high energy gamma
+ d --> pn and gamma + ^3He --> pp + n reactions.Comment: 8 pages Latex, 2 eps figures. Contribution to the conference
"Exclusive Processes at High Momentum Transfer", held at Jefferson Laboratory
May 15-18, 200
Protons in High Density Neutron Matter
We discuss the possible implication of the recent predictions of two new
properties of high momentum distribution of nucleons in asymmetric nuclei for
neutron star dynamics. The first property is about the approximate scaling
relation between proton and neutron high momentum distributions weighted by
their relative fractions ( and ) in the nucleus. The second is the
existence of inverse proportionality of the high momentum distribution strength
of protons and neutrons to . Based on these predictions we model the
high momentum distribution functions for asymmetric nuclei and demonstrate that
it describes reasonably well the high momentum characteristics of light nuclei.
We also extrapolate our results to heavy nuclei as well as infinite nuclear
matter and calculate the relative fractions of protons and neutrons with
momenta above . Our results indicate that for neutron stars starting at
{\em three} nuclear saturation densities the protons with
will populate mostly the high momentum tail of the momentum distribution while
only of the neutrons will do so. Such a situation may have many
implications for different observations of neutron stars which we discuss.Comment: 6 pages, 2 eps figures, For the proceedings of International
Conference on "The Modern Physics of Compact Stars and Relativistic Gravity",
18-21 September 2013, Yerevan, Armeni
Polarization Observables in Hard Rescattering Mechanism of Deuteron Photodisintegration
Polarization properties of high energy photodisintegration of the deuteron
are studied within the framework of the hard rescattering mechanism~(HRM). In
HRM, a quark of one nucleon knocked-out by the incoming photon rescatters with
a quark of the other nucleon leading to the production of two nucleons with
high relative momentum. Summation of all relevant quark rescattering amplitudes
allows us to express the scattering amplitude of the reaction through the
convolution of a hard photon-quark interaction vertex, the large angle p-n
scattering amplitude and the low momentum deuteron wave function. Within HRM,
it is demonstrated that the polarization observables in hard
photodisintegration of the deuteron can be expressed through the five helicity
amplitudes of NN scattering at high momentum transfer. At 90 CM
scattering HRM predicts the dominance of the isovector channel of hard
rescattering, and it explains the observed smallness of induced, and
transfered, polarizations without invoking the argument of helicity
conservation. Namely, HRM predicts that and are proportional to the
helicity amplitude which vanishes at due to
symmetry reasons. HRM predicts also a nonzero value for in the
helicity-conserving regime and a positive asymmetry which is related
to the dominance of the isovector channel in the hard reinteraction. We extend
our calculations to the region where large polarization effects are observed in
scattering as well as give predictions for angular dependences.Comment: Seven pages and three eps figure
Large Q2 Electrodisintegration of the Deuteron in Virtual Nucleon Approximation
The two-body break up of the deuteron is studied at high kinematics,
with main motivation to probe the deuteron at small internucleon distances.
Such studies are associated with the probing of high momentum component of the
deuteron wave function. For this, two main theoretical issues have been
addressed such as electromagnetic interaction of the virtual photon with the
bound nucleon and the strong interaction of produced baryons in the final state
of the break-up reaction. Within virtual nucleon approximation we developed a
new prescription to account for the bound nucleon effects in electromagnetic
interaction. The final state interaction at high kinematics is calculated
within generalized eikonal approximation (GEA). We studied the uncertainties
involved in the calculation and performed comparisons with the first
experimental data on deuteron electrodisintegration at large . We
demonstrate that the experimental data confirm GEA's early prediction that the
rescattering is maximal at of recoil nucleon production relative to
the momentum of the virtual photon. Comparisons also show that the forward
recoil nucleon angles are best suited for studies of the electromagnetic
interaction of bound nucleons and the high momentum structure of the deuteron.
Backward recoil angle kinematics show sizable effects due to the
-isobar contribution. The latter indicates the importance of further
development of GEA to account for the inelastic transitions in the intermediate
state of the electrodisintegration reactions.Comment: 22 pages, 9 figure
Tagged spectator deep-inelastic scattering off the deuteron as a tool to study neutron structure
We give an overview of a model to describe deep-inelastic scattering (DIS)
off the deuteron with a spectator proton, based on the virtual nucleon
approximation (VNA). The model accounts for the final-state interactions (FSI)
of the DIS debris with the spectator proton. Values of the rescattering cross
section are obtained by fits to high-momentum spectator data. By using the
so-called "pole extrapolation method", free neutron structure functions can be
obtained by extrapolating low-momentum spectator proton data to the on-shell
neutron pole. We apply this method to the BONuS data set and find a surprising
Bjorken dependence, indicating a possible rise of the neutron to proton
structure function ratio at high .Comment: 6 pages, 4 figures, proceedings of POETIC
The EMC Effect and Short-Range Correlations
We overview the progress made in studies of EMC and short range correlation
(SRC) effects with the special emphasis given to the recent observation of the
correlation between the slope of the EMC ratio at Bjorken x<1 and the scale
factor of the same ratio at x>1 that measures the strength of the SRCs in
nuclei. This correlation may indicate the larger modification of nucleons with
higher momentum thus making the nucleon virtuality as the most relevant
parameter of medium modifications. To check this conjecture we study the
implication of several properties of high momentum component of the nuclear
wave function on the characteristics of EMC effect. We observe two main reasons
for the EMC-SRC correlation: first, the decrease of the contribution from the
nuclear mean field due to the increase, with A, the fraction of the high
momentum component of nuclear wave function. Second, the increase of the medium
modification of nucleons in SRC. Our main prediction however is the increase of
the proton contribution to the EMC effect for large A asymmetric nuclei. This
prediction is based on the recent observation of the strong dominance of pn
SRCs in the high momentum component of nuclear wave function. Our preliminary
calculation based on this prediction of the excess of energetic and modified
protons in large A nuclei describes reasonably well the main features of the
observed EMC-SRC correlation.Comment: 5 pages, 2 figures, presented at CIPANP 2012 - Eleventh Conference on
the Intersections of Particle and Nuclear Physics, 28 May - 03 June, 201
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