3,512 research outputs found
Proton recoil polarization in exclusive (e,e'pp) reactions
The general formalism of nucleon recoil polarization in the () reaction is given. Numerical predictions are presented for the
components of the outgoing proton polarization and of the polarization transfer
coefficient in the specific case of the exclusive O()C knockout reaction leading to discrete states in the residual
nucleus. Reaction calculations are performed in a direct knockout framework
where final-state interactions and one-body and two-body currents are included.
The two-nucleon overlap integrals are obtained from a calculation of the
two-proton spectral function of O where long-range and short-range
correlations are consistently included. The comparison of results obtained in
different kinematics confirms that resolution of different final states in the
O()C reaction may act as a filter to
disentangle and separately investigate the reaction processes due to
short-range correlations and two-body currents and indicates that measurements
of the components of the outgoing proton polarization may offer good
opportunities to study short-range correlations.Comment: 12 pages, 6 figure
Short-range and tensor correlations in the O(e,epn) reaction
The cross sections for electron induced two-nucleon knockout reactions are
evaluated for the example of the O(e,epn)N reaction leading to
discrete states in the residual nucleus N. These calculations account
for the effects of nucleon-nucleon correlations and include the contributions
of two-body meson exchange currents as the pion seagull, pion in flight and the
isobar current contribution. The effects of short-range as well as tensor
correlations are calculated within the framework of the coupled cluster method
employing the Argonne V14 potential as a model for a realistic nucleon-nucleon
interaction. The relative importance of correlation effects as compared to the
contribution of the meson exchange currents depends on the final state of the
residual nucleus. The cross section leading to specific states, like e.g. the
ground state of N, is rather sensitive to the details of the correlated
wave function.Comment: 16 pages, 9 figures include
Knockout of proton-neutron pairs from O with electromagnetic probes
After recent improvements to the Pavia model of two-nucleon knockout from
O with electromagnetic probes the calculated cross sections are compared
to experimental data from such reactions. Comparison with data from a
measurement of the O(e,epn) reaction show much better agreement
between experiment and theory than was previously observed. In a comparison
with recent data from a measurement of the O(,pn) reaction the
model over-predicts the measured cross section at low missing momentum.Comment: 6 pages, 5 figure
Quenched Hadron Spectrum and Decay Constants on the lattice
In this talk we present the results obtained from a study of
(quenched) lattice configurations from the APE collaboration, at
, using both the Wilson and the SW-Clover fermion action.
We determine the light hadronic spectrum and the meson decay constants. For the
light-light systems we find an agreement with the experimental data of for mesonic masses and for baryonic masses and pseudoscalar
decay constants; a larger deviation is present for the vector decay constants.
For the heavy-light decay constants we find , in good agreement with previous estimates.Comment: 8 pages, latex, Talk given at XXV ITEP Winter School of Physics,
Moscow - Russia, 18-27 Feb 199
Final State Interaction in Exclusive Reactions
Contributions of nucleon-nucleon (NN) correlations, meson exchange currents
and the residual final state interactions (FSI) on exclusive two-nucleon
knock-out reactions induced by electron scattering are investigated. All
contributions are derived from the same realistic meson exchange model for the
NN interaction. Effects of correlations and FSI are determined in a consistent
way by solving the NN scattering equation, the Bethe-Goldstone equation, for
two nucleons in nuclear matter. One finds that the FSI re-scattering terms are
non-negligible even if the two nucleons are emitted back to back.Comment: 8 pages, 5 figure
Deflazacort treatment of cystoid macular edema in patients affected by Retinitis Pigmentosa: a pilot study
Background. To investigate the efficacy of a long-term treatment with Deflazacort (DFZ), a third generation synthetic glucocorticoid, in patients affected by Retinitis Pigmentosa (RP) complicated by Cystoid Macular Edema (CME). Methods. A randomized group of 10 RP subjects were selected for this pilot study and treated with DFZ for one year according to a standard protocol. Far and near Best Corrected Visual Acuity (BCVA), fluorescein angiography (Heidelberg Retina Angiograph) and computerized perimetry (Humphrey Visual Field Analyzer) were statistically assessed. Results. Near visual acuities, fluorescein angiographic findings and perimetric data improved significantly (p < 0.01) while far BCVA varied only slightly (p < 0.05). No ocular or systemic side effects were recorded. Conclusions. Further case-control studies, also involving a larger number of patients, are required to confirm these preliminary results. However, the present investigation seem to suggest that DFZ could be effective in reducing fluorescein angiographic findings and improving perimetric data and near visual acuities in RP patients, even though the pathogenesis of CME remains poorly understood
Clinical pathogenesis of macular holes in patients affected by retinitis pigmentosa
Background. To define the main clinical mechanisms involved in the pathogenesis of macular holes (MH) in patients affected by Retinitis Pigmentosa (RP). Methods. 236 RP subjects were enrolled in this study and ophthalmologically examined according to a standard FIARP (Italian Federation of the RP Associations) protocol. The prevalence of posterior vitreous detachment (PVD) as well as all types of RP-related macular abnormalities - especially vitreoretinal interface alterations (VRIA), cystoid macular edema (CME), "bull's eye maculopathy" (BEM) and MH - was reported; statistical analyses and correlations were assessed by means of Student t test and Pearson X2. Results. VRIA and CME were observed in 26.15% and 9.45% of the cases respectively and resulted significantly associated with MH, since they were constantly present in 22 of the 25 eyes affected by MH (88%) (X2 = 50.4; p < 0.01). In particular, in 9 of these cases (40.9%) MH was correlated to both CME and VRIA, while in 11 (50%) and 2 (9.1%) eyes CME or, VRIA were present separately. A normal biomicroscopic macular appearance, PVD and BEM were found in 26.81%, 6.6% and 21.54% of the cases respectively. Conclusions. Further studies involving a larger number of patients are required to complete these preliminary results. However, the present investigation seem to confirm the data already reported in the literature, i.e. that pathogenesis of MH in RP is strictly correlated to the presence of VRIA, cellophane maculopathy and cystic foveal degeneration with CME
Two-proton overlap functions in the Jastrow correlation method and cross section of the OC reaction
Using the relationship between the two-particle overlap functions (TOF's) and
the two-body density matrix (TDM), the TOF's for the
OC reaction are calculated on the
basis of a TDM obtained within the Jastrow correlation method. The main
contributions of the removal of and pairs from O
are considered in the calculation of the cross section of the
OC reaction using the Jastrow TOF's
which include short-range correlations (SRC). The results are compared with the
cross sections calculated with different theoretical treatments of the TOF's.Comment: 10 pages, 8 figures, ReVTeX
Optimization of Generalized Multichannel Quantum Defect reference functions for Feshbach resonance characterization
This work stresses the importance of the choice of the set of reference
functions in the Generalized Multichannel Quantum Defect Theory to analyze the
location and the width of Feshbach resonance occurring in collisional
cross-sections. This is illustrated on the photoassociation of cold rubidium
atom pairs, which is also modeled using the Mapped Fourier Grid Hamiltonian
method combined with an optical potential. The specificity of the present
example lies in a high density of quasi-bound states (closed channel)
interacting with a dissociation continuum (open channel). We demonstrate that
the optimization of the reference functions leads to quantum defects with a
weak energy dependence across the relevant energy threshold. The main result of
our paper is that the agreement between the both theoretical approaches is
achieved only if optimized reference functions are used.Comment: submitte to Journal of Physics
Probing the chiral weak Hamiltonian at finite volumes
Non-leptonic kaon decays are often described through an effective chiral weak
Hamiltonian, whose couplings ("low-energy constants") encode all
non-perturbative QCD physics. It has recently been suggested that these
low-energy constants could be determined at finite volumes by matching the
non-perturbatively measured three-point correlation functions between the weak
Hamiltonian and two left-handed flavour currents, to analytic predictions
following from chiral perturbation theory. Here we complete the analytic side
in two respects: by inspecting how small ("epsilon-regime") and intermediate or
large ("p-regime") quark masses connect to each other, and by including in the
discussion the two leading Delta I = 1/2 operators. We show that the
epsilon-regime offers a straightforward strategy for disentangling the
coefficients of the Delta I = 1/2 operators, and that in the p-regime
finite-volume effects are significant in these observables once the
pseudoscalar mass M and the box length L are in the regime ML \lsim 5.0.Comment: 37 pages. v2: some additions and clarifications; published versio
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