374 research outputs found
Angular distribution and azimuthal asymmetry for pentaquark production in proton-proton collisions
Angular distributions for production of the pentaquark are
calculated for the collisions of polarized protons with polarized target
protons. We compare calculations based on different assumptions concerning spin
and parity () of the state. For a wide class of
interactions the spin correlation parameters describing the asymmetric angular
distributions are calculated up to 250 MeV above production threshold. The
deviations from the near threshold behavior are investigated.Comment: 8 pages, 5 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
Measurement of Spin Correlation Parameters A, A, and A_ at 2.1 GeV in Proton-Proton Elastic Scattering
At the Cooler Synchrotron COSY/J\"ulich spin correlation parameters in
elastic proton-proton (pp) scattering have been measured with a 2.11 GeV
polarized proton beam and a polarized hydrogen atomic beam target. We report
results for A, A, and A_ for c.m. scattering angles between
30 and 90. Our data on A -- the first measurement of this
observable above 800 MeV -- clearly disagrees with predictions of available of
pp scattering phase shift solutions while A and A_ are reproduced
reasonably well. We show that in the direct reconstruction of the scattering
amplitudes from the body of available pp elastic scattering data at 2.1 GeV the
number of possible solutions is considerably reduced.Comment: 4 pages, 4 figure
Two-Pion Exchange in Proton-Proton Scattering
The contribution of the box and crossed two-pion-exchange diagrams to
proton-proton scattering at 90 is calculated in the laboratory
momentum range up to 12 GeV/c. Relativistic form factors related to the nucleon
and pion size and representing the pion source distribution based on the quark
structure of the hadronic core are included at each vertex of the pion-nucleon
interaction. These form factors depend on the four-momenta of the exchanged
pions and scattering nucleons. Feynman-diagram amplitudes calculated without
form factors are checked against those derived from dispersion relations. In
this comparison, one notices that a very short-range part of the crossed
diagram, neglected in dispersion-relation calculations of the two-pion-exchange
nucleon-nucleon potential, gives a sizable contribution. In the Feynman-diagram
calculation with form factors the agreement with measured spin-separated cross
sections, as well as amplitudes in the lower part of the energy range
considered, is much better for pion-nucleon pseudo-vector vis \`a vis
pseudo-scalar coupling. While strengths of the box and crossed diagrams are
comparable for laboratory momenta below 2 GeV/c, the crossed diagram dominates
for larger momenta, largely due to the kinematics of the crossed diagram
allowing a smaller momentum transfer in the nucleon center of mass. An
important contribution arises from the principal-value part of the integrals
which is non-zero when form factors are included. It seems that the importance
of the exchange of color singlets may extend higher in energy than expected
Nucleon-Nucleon Optical Model for Energies to 3 GeV
Several nucleon-nucleon potentials, Paris, Nijmegen, Argonne, and those
derived by quantum inversion, which describe the NN interaction for T-lab below
300$ MeV are extended in their range of application as NN optical models.
Extensions are made in r-space using complex separable potentials definable
with a wide range of form factor options including those of boundary condition
models. We use the latest phase shift analyses SP00 (FA00, WI00) of Arndt et
al. from 300 MeV to 3 GeV to determine these extensions. The imaginary parts of
the optical model interactions account for loss of flux into direct or resonant
production processes. The optical potential approach is of particular value as
it permits one to visualize fusion, and subsequent fission, of nucleons when
T-lab above 2 GeV. We do so by calculating the scattering wave functions to
specify the energy and radial dependences of flux losses and of probability
distributions. Furthermore, half-off the energy shell t-matrices are presented
as they are readily deduced with this approach. Such t-matrices are required
for studies of few- and many-body nuclear reactions.Comment: Latex, 40 postscript pages including 17 figure
Analysis of NN Amplitudes up to 2.5 GeV: An Optical Model and Geometric Interpretation
We analyse the SM97 partial wave amplitudes for nucleon--nucleon (NN)
scattering to 2.5 GeV, in which resonance and meson production effects are
evident for energies above pion production threshold. Our analyses are based
upon boson exchange or quantum inversion potentials with which the
sub-threshold data are fit perfectly. Above 300 MeV they are extrapolations, to
which complex short ranged Gaussian potentials are added in the spirit of the
optical models of nuclear physics and of diffraction models of high energy
physics. The data to 2.5 GeV are all well fit. The energy dependences of these
Gaussians are very smooth save for precise effects caused by the known
and N resonances. With this approach, we confirm that the geometrical
implications of the profile function found from diffraction scattering are
pertinent in the regime 300 MeV to 2.5 GeV and that the overwhelming part of
meson production comes from the QCD sector of the nucleons when they have a
separation of their centres of 1 to 1.2 fm. This analysis shows that the
elastic NN scattering data above 300 MeV can be understood with a local
potential operator as well as has the data below 300 MeV.Comment: 49 pages, including 23 figures, LaTeX2e/RevTeX/ps fil
Spin dependence of the antinucleon-nucleon interaction
The status of our present knowledge on the antinucleon-nucleon interaction at
low and medium energies is discussed. Special emphasis is put on aspects
related to its spin dependence which are relevant for experiments planned by
the PAX collaboration. Predictions for the spin-dependent antiproton-proton
cross sections sigma_1 and sigma_2 are presented, utilizing antinucleon-nucleon
potential models developed by the Juelich group, and compared to results based
on the amplitudes of the Nijmegen partial-wave analysis.Comment: 8 pages, 4 figures, to appear in the proceedings of the 19th
International Spin Physics Symposium, September 27 - October 2, 2010,
Juelich, German
Precise method for the determination of the neutron electric form factor based on a relativistic analysis of the process $d(e,e'n)p
We generalize the recoil polarization method for the determination of the
proton form factor to the case of the disintegration of vector polarized
deuterons by longitudinally polarized electrons, . We
suggest to measure for this reaction, in the kinematics of quasi-elastic
-scattering, the ratio of the asymmetries induced by the
- and -components of the deuteron vector polarization. In the framework
of the relativistic impulse approximation the ratio is sensitive to
in a wide interval of momentum transfer squared, whereas it depends
weakly on the details of the -interaction and on the choice of the deuteron
wave function. Moreover, in the range 1.5 GeV, the ratio
shows a smooth dependence on , making the analysis simpler.Comment: 7 pages, 4 figs, 1 tabl
Big Bang Nucleosynthesis Constraints on Hadronically and Electromagnetically Decaying Relic Neutral Particles
Big Bang nucleosynthesis in the presence of decaying relic neutral particles
is examined in detail. All non-thermal processes important for the
determination of light-element abundance yields of 2H, 3H, 3He, 4He, 6Li, and
7Li are coupled to the thermonuclear fusion reactions to obtain comparatively
accurate results. Predicted light-element yields are compared to
observationally inferred limits on primordial light-element abundances to infer
constraints on the abundances and properties of relic decaying particles with
decay times in the interval 0.01 sec < tau < 10^(12) sec. Decaying particles
are typically constrained at early times by 4He or 2H, at intermediate times by
6Li, and at large times by the 3He/2H ratio. Constraints are shown for a large
number of hadronic branching ratios and decaying particle masses and may be
applied to constrain the evolution of the early Universe.Comment: 24 pages (revtex), 11 figures, title changed, matches published
versio
Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Réunion and Hawaii hotspot islands
Surface volcanism at la Réunion and Hawaii occurs with an offset of 150–180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around ∼50–70 km depth where the temperature varies from ∼600 °C to ∼750 °C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at ∼50–70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., ∼150 km away from the plume head. There, melts propagate through dikes upwards to ∼35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30–35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30–35 km depth and compression at ∼15 km depth (induced by the edifice load). It implies that now the melts pond at ∼15 km and form another magmatic reservoir lying just underneath the crust. These processes explain the ponding of primary (shield) melts at ∼35 km and ∼15 km depths as recorded below La Reunion, Mauritius or Hawaii volcanoes, all shifted by ∼150 km with respect to the plume axis
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