29,283 research outputs found
A unified approach to electron and neutrino elastic scattering off nuclei with an application to the study of the axial structure
We show a relationship between elastic electron scattering observables and
the elastic neutrino cross section that provides a straightforward
determination of the latter from experimental data of the former and relates
their uncertainties. An illustration of this procedure is presented using a
Hartree-Fock mean field for the nuclear structure of a set of even-even nuclear
targets, using the spectra of the neutrinos produced in pion decay at rest. We
also analyze the prospects to measure the incoherent axial contribution to the
neutrino elastic scattering in odd targets
Coincidence charged-current neutrino-induced deuteron disintegration for
Semi-inclusive charge-changing neutrino reactions on targets of heavy water
are investigated with the goal of determining the relative contributions to the
total cross section of deuterium and oxygen in kinematics chosen to emphasize
the former. The study is undertaken for conditions where the typical neutrino
beam energies are in the few GeV region, and hence relativistic modeling is
essential. For this, the previous relativistic approach for the deuteron is
employed, together with a spectral function approach for the case of oxygen.
Upon optimizing the kinematics of the final-state particles assumed to be
detected (typically a muon and a proton) it is shown that the oxygen
contribution to the total cross section is suppressed by roughly an order of
magnitude compared with the deuterium cross section, thereby confirming that
CC studies of heavy water can effectively yield the cross sections for
deuterium, with acceptable backgrounds from oxygen. This opens the possibility
of using deuterium to determine the incident neutrino flux distribution, to
have it serve as a target for which the nuclear structure issues are minimal,
and possibly to use deuterium to provide improved knowledge of specific aspects
of hadronic structure, such as to explore the momentum transfer dependence of
the isovector axial-vector form factor of the nucleon
Semi-inclusive charged-current neutrino-nucleus reactions
The general, universal formalism for semi-inclusive charged-current
(anti)neutrino-nucleus reactions is given for studies of any hadronic system,
namely, either nuclei or the nucleon itself. The detailed developments are
presented with the former in mind and are further specialized to cases where
the final-state charged lepton and an ejected nucleon are presumed to be
detected. General kinematics for such processes are summarized and then
explicit expressions are developed for the leptonic and hadronic tensors
involved and for the corresponding responses according to the usual charge,
longitudinal and transverse projections, keeping finite the masses of all
particles involved. In the case of the hadronic responses, general symmetry
principles are invoked to determine which contributions can occur. Finally, the
general leptonic-hadronic tensor contraction is given as well as the cross
section for the process
Coincidence charged-current neutrino-induced deuteron disintegration
Deuteron disintegration by charged-current neutrino (CC) scattering
offers the possibility to determine the energy of the incident neutrino by
measuring in coincidence two of the three resulting particles: a charged lepton
(usually a muon) and two protons, where we show that this channel can be
isolated from all other, for instance, from those with a pion in the final
state. We discuss the kinematics of the process for several detection
scenarios, both in terms of kinematic variables that are natural from a
theoretical point of view and others that are better matched to experimental
situations. The deuteron structure is obtained from a relativistic model
(involving an approximation to the Bethe-Salpeter equation) as an extension of
a previous, well-tested model used in deuteron electrodisintegration. We
provide inclusive and coincidence (semi-inclusive) cross sections for a variety
of kinematic conditions, using the plane-wave impulse approximation,
introducing final-state hadronic exchange terms (plane-wave Born approximation)
and final-state hadronic interactions (distorted-wave Born approximation).Comment: 31 pages, 14 figure
The physics of twisted magnetic tubes rising in a stratified medium: two dimensional results
The physics of a twisted magnetic flux tube rising in a stratified medium is
studied using a numerical MHD code. The problem considered is fully
compressible (no Boussinesq approximation), includes ohmic resistivity, and is
two dimensional, i.e., there is no variation of the variables in the direction
of the tube axis. We study a high plasma beta case with small ratio of radius
to external pressure scaleheight. The results obtained can therefore be of
relevance to understand the transport of magnetic flux across the solar
convection zone.Comment: To be published in ApJ, Vol. 492, Jan 10th, 1998; 25 pages, 16
figures. NEW VERSION: THE PREVIOUS ONE DIDN'T PRINT CORRECTLY. The style file
overrulehere.sty is include
The design of an automated verification of redundant systems
Handbook describes design processes, presents design considerations and techniques, gives tutorial material on implementation and methodology, shows design aids, illustrates use of design aids and application samples, and identifies general practices to be adhered to or avoided
The effect of the relative orientation between the coronal field and new emerging flux: I Global Properties
The emergence of magnetic flux from the convection zone into the corona is an
important process for the dynamical evolution of the coronal magnetic field. In
this paper we extend our previous numerical investigations, by looking at the
process of flux interaction as an initially twisted flux tube emerges into a
plane parallel, coronal magnetic field. Significant differences are found in
the dynamical appearance and evolution of the emergence process depending on
the relative orientation between the rising flux system and any preexisting
coronal field. When the flux systems are nearly anti-parallel, the experiments
show substantial reconnection and demonstrate clear signatures of a high
temperature plasma located in the high velocity outflow regions extending from
the reconnection region. However, the cases that have a more parallel
orientation of the flux systems show very limited reconnection and none of the
associated features. Despite the very different amount of reconnection between
the two flux systems, it is found that the emerging flux that is still
connected to the original tube, reaches the same height as a function of time.
As a compensation for the loss of tube flux, a clear difference is found in the
extent of the emerging loop in the direction perpendicular to the main axis of
the initial flux tube. Increasing amounts of magnetic reconnection decrease the
volume, which confines the remaining tube flux.Comment: 21 pages, 16 figures Accepted for Ap
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