2,227 research outputs found
Spin dependent Momentum Distributions in Deformed Nuclei
We study the properties of the spin dependent one body density in momentum
space for odd--A polarized deformed nuclei within the mean field approximation.
We derive analytic expressions connecting intrinsic and laboratory momentum
distributions. The latter are related to observable transition densities in
{\bf p}--space that can be probed in one nucleon knock--out reactions from
polarized targets. It is shown that most of the information contained in the
intrinsic spin dependent momentum distribution is lost when the nucleus is not
polarized. Results are presented and discussed for two prolate nuclei,
Ne and Mg, and for one oblate nucleus, Ar. The effects of
deformation are highlighted by comparison to the case of odd--A nuclei in the
spherical model.Comment: Latex 2.09. 25 pages and 6 figures (available from
[email protected]), to appear in Ann. of Phy
Inclusive quasielastic electron scattering on He: a probe of the halo structure
We investigate inclusive electron scattering reactions on two-neutron halo
nuclei in the quasielastic region. Expressions for the cross section and
structure functions are given assuming that the halo nucleus can be described
as a three-body system (). The method is applied to He. We
compute cross sections and structure functions, and investigate the kinematic
conditions for which the observables are determined either by -knockout
or by halo neutron-knockout. The optimal kinematical domain to disantangle the
momentum distributions of the various components of the three--body system ( MeV/c and MeV) are explored.Comment: 10 pages, 3 figures. Physics Letters B, in pres
Inclusive quasielastic scattering of polarized electrons from polarized nuclei
The inclusive quasielastic response functions that appear in the scattering
of polarized electrons from polarized nuclei are computed and analyzed for
several closed-shell-minus-one nuclei with special attention paid to 39K.
Results are presented using two models for the ejected nucleon --- when
described by a distorted wave in the continuum shell model or by a plane wave
in PWIA with on- and off-shell nucleons. Relativistic effects in kinematics and
in the electromagnetic current have been incorporated throughout. Specifically,
the recently obtained expansion of the electromagnetic current in powers only
of the struck nucleon's momentum is employed for the on-shell current and the
effects of the first-order terms (spin-orbit and convection) are compared with
the zeroth-order (charge and magnetization) contributions. The use of polarized
inclusive quasielastic electron scattering as a tool for determining
near-valence nucleon momentum distributions is discussed.Comment: 51 LaTeX pages, 14 Postscript figure
Electron scattering on two-neutron halo nuclei: The case of He
The formalism to describe electron scattering reactions on two-neutron halo
nuclei is developed. The halo nucleus is described as a three-body system
(core+n+n), and the wave function is obtained by solving the Faddeev equations
in coordinate space. We discuss elastic and quasielastic scattering using the
impulse approximation to describe the reaction mechanism. We apply the method
to investigate the case of electron scattering on He. Spectral functions,
response functions, and differential cross sections are calculated for both
neutron knockout and knockout by the electron.Comment: 17 pages, figures include
Probing Deformed Orbitals with \vec{A}(\vec{e}, e' N)B reactions
We present results for response functions and asymmetries in the nuclear
reactions 37\vec{Ar}(\vec{e},e'n)36Ar and 37\vec{K}(\vec{e},e' p)36Ar at
quasifree kinematics. We compare PWIA results obtained using deformed HF wave
functions with PWIA and DWIA results obtained assuming a spherical mean field.
We show that the complex structure of the deformed orbitals can be probed by
coincidence measurements with polarized beam and targets.Comment: Latex 2.09. 22 pages and 8 figures (available from
[email protected]), to appear in Nuc. Phys.
Polarized Deformed Nuclei Studied via Coincidence Polarized Electron Scattering: The case of 21 Ne
Coincidence reactions of the type \svec{A}(\svec{e},e'N)B involving the
scattering of polarized electrons from deformed polarized targets are discussed
within the context of the plane--wave impulse approximation. A general
expression for the polarized spectral function for transitions leaving the
residual nucleus in discrete states is presented. General properties and
angular symmetries exhibited by the polarization observables are discussed in
detail. Results for unpolarized cross sections as well as for polarization
ratios (asymmetries) are obtained for typical quasi--free kinematics. The
dependences of the polarization observables on the bound neutron momentum,
target polarization orientation, nuclear deformation and value of the momentum
transfer are discussed in detail for various different kinematical
situations.Comment: 37 pages in Plain TeX, MIT-CTP-209
Spectroscopic Factors in Ca and Pb from : Fully Relativistic Analysis
We present results for spectroscopic factors of the outermost shells in
Ca and Pb, which have been derived from the comparison between
the available quasielastic () data from NIKHEF-K and the corresponding
calculated cross-sections obtained within a fully relativistic formalism. We
include exactly the effect of Coulomb distortion on the electron wave functions
and discuss its role in the extraction of the spectroscopic factors from
experiment. Without any adjustable parameter, we find spectroscopic factors of
about 70\%, consistent with theoretical predictions. We compare our results
with previous relativistic and nonrelativistic analyses of () data. In
addition to Coulomb distortion effects we discuss different choices of the
nucleon current operator and also analyze the effects due to the relativistic
treatment of the outgoing-distorted and bound nucleon wave functions.Comment: 9 pages RevTeX, 5 figures can be obtained from the author
Candidate free-floating super-Jupiters in the young sigma Orionis open cluster
Free-floating substellar candidates with estimated theoretical masses of as
low as ~5 Jupiter masses have been found in the ~3 Myr old sigma Orionis open
cluster. As the overlap with the planetary mass domain increases, the question
of how these objects form becomes important. The determination of their number
density and whether a mass cut-off limit exists is crucial to understanding
their formation. We propose to search for objects of yet lower masses in the
cluster and determine the shape of the mass function at low mass. Using new-
and (re-analysed) published IZJHKs[3.6]-[8.0]-band data of an area of 840
arcmin2, we performed a search for LT-type cluster member candidates in the
magnitude range J=19.5-21.5 mag, based on their expected magnitudes and
colours. Besides recovering the T type object S Ori 70 and two other known
objects, we find three new cluster member candidates, S Ori 72-74, with J=21
mag and within 12 arcmin of the cluster centre. They have theoretical masses of
4 (-2,+3) M_Jup and are among the least massive free-floating objects detected
by direct imaging outside the Solar System. The photometry in archival Spitzer
[3.6]-[5.8]-band images infers that S Ori 72 is an L/T transition candidate and
S Ori 73 a T-type candidate, following the expected cluster sequence in the
mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality
photometry is located at 11.8 arcsec (~4250 AU) of a stellar member of sigma
Orionis and could be a companion. After contaminant correction in the area
complete to J=21.1 mag, we estimate that there remain between zero and two
cluster members in the mass interval 6-4 M_Jup. Our result suggests a possible
turnover in the substellar mass spectrum below ~6 Jupiter masses, which could
be investigated further by wider and deeper photometric surveys.Comment: 15 pages, 13 figures, 5 tables, and appendix containing 5 figures;
accepted for publication in AA; v2: 2 minor corrections, in abstract and
sect. 2.
Relativistic versus Nonrelativistic Optical Potentials in A(e,e'p)B Reactions
We investigate the role of relativistic and nonrelativistic optical
potentials used in the analysis of () data. We find that the
relativistic calculations produce smaller () cross sections even in the
case in which both relativistic and nonrelativistic optical potentials fit
equally well the elastic proton--nucleus scattering data. Compared to the
nonrelativistic impulse approximation, this effect is due to a depletion in the
nuclear interior of the relativistic nucleon current, which should be taken
into account in the nonrelativistic treatment by a proper redefinition of the
effective current operator.Comment: Added one new figure, the formalism section has been enlarged and the
list of references updated. Added one appendix. This version will appear in
Phys. Rev. C. Revtex 3.0, 6 figures (not included). Full postscript version
of the file and figures available at
http://www.nikhefk.nikhef.nl/projects/Theory/preprints
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