508 research outputs found
Proton polarizations in polarized 3He studied with the \vec{3He} (\vec{e},e' p)d and \vec{3He} (\vec{e},e' p)pn processes
We study within the Faddeev framework the \vec{3He} (\vec{e},e' p)d as well
as the \vec{3He} (\vec{e},e' p)pn and \vec{3He} (\vec{e},e' n)pp reactions in
order to extract information on the proton and neutron polarization in
polarized 3He. We achieve clear analytical insight for simplified dynamical
assumptions and define conditions for experimental access to important 3He
properties. In addition we point to the possibility to measure the
electromagnetic proton form factors in the process \vec{3He} (\vec{e},e' p)d
which would test the dynamical picture and put limits on medium corrections of
the form factors.Comment: 38 pages, 22 figure
Nucleon-deuteron capture with chiral potentials
Present day chiral nucleon-nucleon potentials up to N3LO and three nucleon
forces at N2LO are used to analyze nucleon-deuteron radiative capture at
deuteron lab energies below E_d= 100 MeV. The differential cross section and
the deuteron analyzing powers A_y(d) and A_{yy} are presented and compared to
data. The theoretical predictions are obtained in the momentum-space Faddeev
approach using the nuclear electromagnetic current operator with exchange
currents introduced via the Siegert theorem. The chiral forces provide the same
quality of data description as a combination of the two-nucleon AV18 and the
three-nucleon Urbana IX interactions. However, the different parametrizations
of the chiral potentials lead to broad bands of predictions.Comment: 20 pages, 12 ps figure
Spin dependent momentum distributions of proton-deuteron clusters in 3He from electron scattering on polarized 3He: theoretical predictions
The process (or
) is studied theoretically in a
Faddeev treatment with the aim to have access to the spin-dependent momentum
distribution of clusters in polarized He. Final state
interactions and meson exchange currents turn out to have a strong influence in
the considered kinematical regime (below the pion threshold). This precludes
the direct access to the momentum distribution except for small deuteron
momenta. Nevertheless, the results for the longitudinal and transverse response
functions are interesting as they reflect our present day understanding of the
reaction mechanism and therefore data would be very useful.Comment: 16 pages, 9 figure
On the usefulness of the spectral function concept
The usefulness of the spectral function S in the process 3He(e,e'N) has been
investigated in a kinematical regime constrained by the conditions that the
three-nucleon center-of-mass energy is less than 150 MeV and the magnitude of
the three-momentum transfer smaller than 600 MeV/c. Results based on a full
treatment of the final state interaction are compared to the spectral function
approximation. In the case of proton knockout in the direction of the photon
kinematical conditions have been identified where both response functions, RL
and RT, can be well approximated by S. These conditions occur for certain low
missing momenta and missing energies but not in all cases. So care is required.
In case of neutron knockout only RT is a candidate for an approximate treatment
by S. In the case of RL the concept of using S is not valid in the studied
kinematical regime. This does not exclude the possibility that beyond that
regime it might be useful. Possible applications using S for the extraction of
electromagnetic form factors of the nucleons are pointed out.Comment: 27 pages, 25 fugure
Search for Three-Nucleon Force Effects in Two-Body Photodisintegration of 3He(3H) and in the Time Reversed Proton-Deuteron Radiative Capture Process
Faddeev calculations have been performed for nucleon-deuteron
photodisintegration of 3He(3H) and proton-deuteron radiative capture. The bulk
of the results is based on the AV18 nucleon-nucleon force and the Urbana IX
three-nucleon force together with explicit exchange currents or applying the
Siegert approach. Three-nucleon force effects are predicted for both processes
and supported by most of the data.Comment: 21 pages, 8 figures, modified version with changed figures,
conclusions unchanged, to appear in Phys.Rev.
Theoretical predictions for extraction of GEn from semi-inclusive electron scattering on polarized 3He based on various nucleon-nucleon interactions
The process 3He(e,e'n) with polarized electrons and 3He in the initial state
is theoretically analyzed with the aim to search for sensitivity to the
electric form factor of the neutron, GEn. Faddeev calculations based on five
high precision nucleon-nucleon force models are employed and stability versus
exchange of the nucleon-nucleon forces is demonstrated.Comment: 7 pages, 3 Postscript figure
Optimizing XML Compression
The eXtensible Markup Language (XML) provides a powerful and flexible means
of encoding and exchanging data. As it turns out, its main advantage as an
encoding format (namely, its requirement that all open and close markup tags
are present and properly balanced) yield also one of its main disadvantages:
verbosity. XML-conscious compression techniques seek to overcome this drawback.
Many of these techniques first separate XML structure from the document
content, and then compress each independently. Further compression gains can be
realized by identifying and compressing together document content that is
highly similar, thereby amortizing the storage costs of auxiliary information
required by the chosen compression algorithm. Additionally, the proper choice
of compression algorithm is an important factor not only for the achievable
compression gain, but also for access performance. Hence, choosing a
compression configuration that optimizes compression gain requires one to
determine (1) a partitioning strategy for document content, and (2) the best
available compression algorithm to apply to each set within this partition. In
this paper, we show that finding an optimal compression configuration with
respect to compression gain is an NP-hard optimization problem. This problem
remains intractable even if one considers a single compression algorithm for
all content. We also describe an approximation algorithm for selecting a
partitioning strategy for document content based on the branch-and-bound
paradigm.Comment: 16 pages, extended version of paper accepted for XSym 200
Break-up channels in muon capture on 3He
The mu + 2H -> nu + n + n, mu + 3He -> nu + 3H, mu + 3He -> nu + n + d and mu
+ 3He -> nu + n + n + p capture reactions are studied with various realistic
potentials under full inclusion of final state interactions. Our results for
the two- and three-body break-up of 3He are calculated with a variety of
nucleon-nucleon potentials, among which is the AV18 potential, augmented by the
Urbana~IX three-nucleon potential. Most of our results are based on the single
nucleon weak current operator. As a first step, we have tested our calculation
in the case of the mu + 2H -> nu + n + n and mu + 3He -> nu + 3H reactions, for
which theoretical predictions obtained in a comparable framework are available.
Additionally, we have been able to obtain for the first time a realistic
estimate for the total rates of the muon capture reactions on 3He in the
break-up channels: 544 1/s and 154 1/s for the n + d and n + n + p channels,
respectively. Our results have also been compared with the most recent
experimental data, finding a rough agreement for the total capture rates, but
failing to reproduce the differential capture rates.Comment: 29 pages, 18 figure
Nucleon-deuteron scattering with the JISP16 potential
The nucleon-nucleon J-matrix Inverse Scattering Potential JISP16 is applied
to elastic nucleon-deuteron (Nd) scattering and the deuteron breakup process at
the lab. nucleon energies up to 135 MeV. The formalism of the Faddeev equations
is used to obtain 3N scattering states. We compare predictions based on the
JISP16 force with data and with results based on various NN interactions: the
CD Bonn, the AV18, the chiral force with the semi-local regularization at the
5th order of the chiral expansion and with low-momentum interactions obtained
from the CD Bonn force as well as with the predictions from the combination of
the AV18 NN interaction and the Urbana IX 3N force. JISP16 provides a
satisfactory description of some observables at low energies but strong
deviations from data as well as from standard and chiral potential predictions
with increasing energy. However, there are also polarization observables at low
energies for which the JISP16 predictions differ from those based on the other
forces by a factor of two. The reason for such a behavior can be traced back to
the P-wave components of the JISP16 force. At higher energies the deviations
can be enhanced by an interference with higher partial waves and by the
properties of the JISP16 deuteron wave function. In addition, we compare the
energy and angular dependence of predictions based on the JISP16 force with the
results of the low-momentum forces obtained with different values of the
momentum cutoff parameter. We found that such low-momentum forces can be
employed to interpret the Nd elastic scattering data only below some specific
energy which depends on the cutoff parameter. Since JISP16 is defined in a
finite oscillator basis, it has properties similar to low momentum interactions
and its application to the description of Nd scattering data is limited to a
low momentum transfer region.Comment: 26 pages, 12 eps figures; Version accepted to Phys. Rev. C: text is
shortened, few figures regarding the nucleon-deuteron elastic scattering
observables are removed but a short discussion of the nucleon induced
deuteron breakup cross section is added. Conclusions remain unchange
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