3,314 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
Variable-order fractional calculus: A change of perspective
Several approaches to the formulation of a fractional theory of calculus of âvariable orderâ have appeared in the literature over the years. Unfortunately, most of these proposals lack a rigorous mathematical framework. We consider an alternative view on the problem, originally proposed by G. Scarpi in the early seventies, based on a naive modification of the representation in the Laplace domain of standard kernels functions involved in (constant-order) fractional calculus. We frame Scarpi's ideas within recent theory of General Fractional Derivatives and Integrals, that mostly rely on the Sonine condition, and investigate the main properties of the emerging variable-order operators. Then, taking advantage of powerful and easy-to-use numerical methods for the inversion of Laplace transforms of functions defined in the Laplace domain, we discuss some practical applications of the variable-order Scarpi integral and derivative
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
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
f_K/f_pi in Full QCD with Domain Wall Valence Quarks
We compute the ratio of pseudoscalar decay constants f_K/f_pi using
domain-wall valence quarks and rooted improved Kogut-Susskind sea quarks. By
employing continuum chiral perturbation theory, we extract the Gasser-Leutwyler
low-energy constant L_5, and extrapolate f_K/f_pi to the physical point. We
find: f_K/f_pi = 1.218 (+- 0.002) (+0.011 -0.024) where the first error is
statistical and the second error is an estimate of the systematic due to chiral
extrapolation and fitting procedures. This value agrees within the
uncertainties with the determination by the MILC collaboration, calculated
using Kogut-Susskind valence quarks, indicating that systematic errors arising
from the choice of lattice valence quark are small.Comment: 14 pages, 9 figure
Two-nucleon emission in the longitudinal response
The contribution of the two-nucleon emission in the longitudinal response for
inclusive electron scattering reactions is studied. The model adopted to
perform the calculations is based upon Correlated Basis Function theory but it
considers only first order terms in the correlation function. The proper
normalization of the wave function is ensured by considering, in addition to
the usually evaluated two-point diagrams, also the three-point diagrams.
Results for the 12C nucleus in the quasi-elastic region are presented.Comment: 7 pages, 4 Postscript figure
A Study of the 't Hooft Model with the Overlap Dirac Operator
We present the results of an exploratory numerical study of two dimensional
QCD with overlap fermions. We have performed extensive simulations for U(N_c)
and SU(N_c) color groups with N_c=2, 3, 4 and coupling constants chosen to
satisfy the 't Hooft condition g^2 N_c =const=4/3. We have computed the meson
spectrum and decay constants, the topological susceptibility and the chiral
condensate. For U(N_c) gauge groups, our results indicate that the
Witten-Veneziano relation is satisfied within our statistical errors and that
the chiral condensate for N_f=1 is compatible with a non-zero value. Our
results exhibit universality in N_c and confirm once more the excellent chiral
properties of the overlap-Dirac operator.Comment: 18 pages, 4 figure
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
The AMS-02 Time of Flight System. Final Design
The AMS-02 detector is a superconducting magnetic spectrometer that will
operate on the International Space Station. The time of flight (TOF) system of
AMS-02 is composed by four scintillator planes with 8, 8, 10, 8 counters each,
read at both ends by a total of 144 phototubes. This paper describes the new
design, the expected performances, and shows preliminary results of the ion
beam test carried on at CERN on October 2002.Comment: 4 pages, 6 EPS figures. Proc. of the 28th ICRC (2003
- âŠ