6,799 research outputs found
Momentum Space Integral Equations for Three Charged Particles: Diagonal Kernels
It has been a long-standing question whether momentum space integral
equations of the Faddeev type are applicable to reactions of three charged
particles, in particular above the three-body threshold. For, the presence of
long-range Coulomb forces has been thought to give rise to such severe
singularities in their kernels that the latter may lack the compactness
property known to exist in the case of purely short-range interactions.
Employing the rigorously equivalent formulation in terms of an
effective-two-body theory we have proved in a preceding paper [Phys. Rev. C
{\bf 61}, 064006 (2000)] that, for all energies, the nondiagonal kernels
occurring in the integral equations which determine the transition amplitudes
for all binary collision processes, possess on and off the energy shell only
integrable singularities, provided all three particles have charges of the same
sign, i.e., all Coulomb interactions are repulsive. In the present paper we
prove that, for particles with charges of equal sign, the diagonal kernels, in
contrast, possess one, but only one, nonintegrable singularity. The latter can,
however, be isolated explicitly and dealt with in a well-defined manner. Taken
together these results imply that modified integral equations can be
formulated, with kernels that become compact after a few iterations. This
concludes the proof that standard solution methods can be used for the
calculation of all binary (i.e., (in-)elastic and rearrangement) amplitudes by
means of momentum space integral equations of the effective-two-body type.Comment: 36 pages, 2 figures, accepted for publication in Phys. Rev.
Proton-Deuteron Elastic Scattering from 2.5 to 22.5 MeV
We present the results of a calculation of differential cross sections and
polarization observables for proton-deuteron elastic scattering, for proton
laboratory energies from 2.5 to 22.5 MeV. The Paris potential parametrisation
of the nuclear force is used. As solution method for the charged-composite
particle equations the 'screening and renormalisation approach' is adopted
which allows to correctly take into account the Coulomb repulsion between the
two protons. Comparison is made with the precise experimental data of Sagara et
al. [Phys. Rev. C 50, 576 (1994)] and of Sperison et al. [Nucl. Phys. A422, 81
(1984)].Comment: 24 pages, 8 eps figures, uses REVTe
Nuclear modification at sqrt{s_{NN}}=17.3 GeV, measured at NA49
Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity
in Pb+Pb reactions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-},
by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and
R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV.
The modification factor R_{AA} shows a rapid increase with transverse momentum
in the covered region. The modification factor R_{CP} shows saturation well
below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200
GeV RHIC results closely in the available transverse momentum range for all
particle species. For pi^{+/-} above 2.5 GeV/c transverse momentum, the
measured suppression is smaller than that observed at RHIC. The nuclear
modification factor R_{AA/pA} for pi^{+/-} stays well below unity.Comment: Proceedings of Quark Matter 2008 conferenc
Precision preparation of strings of trapped neutral atoms
We have recently demonstrated the creation of regular strings of neutral
caesium atoms in a standing wave optical dipole trap using optical tweezers [Y.
Miroshnychenko et al., Nature, in press (2006)]. The rearrangement is realized
atom-by-atom, extracting an atom and re-inserting it at the desired position
with sub-micrometer resolution. We describe our experimental setup and present
detailed measurements as well as simple analytical models for the resolution of
the extraction process, for the precision of the insertion, and for heating
processes. We compare two different methods of insertion, one of which permits
the placement of two atoms into one optical micropotential. The theoretical
models largely explain our experimental results and allow us to identify the
main limiting factors for the precision and efficiency of the manipulations.
Strategies for future improvements are discussed.Comment: 25 pages, 18 figure
Long-range behavior of the optical potential for the elastic scattering of charged composite particles
The asymptotic behavior of the optical potential, describing elastic
scattering of a charged particle off a bound state of two charged, or
one charged and one neutral, particles at small momentum transfer
or equivalently at large intercluster distance
, is investigated within the framework of the exact three-body
theory. For the three-charged-particle Green function that occurs in the exact
expression for the optical potential, a recently derived expression, which is
appropriate for the asymptotic region under consideration, is used. We find
that for arbitrary values of the energy parameter the non-static part of the
optical potential behaves for as
. From this we derive for the
Fourier transform of its on-shell restriction for the behavior , i.e.,
dipole or quadrupole terms do not occur in the coordinate-space asymptotics.
This result corroborates the standard one, which is obtained by perturbative
methods. The general, energy-dependent expression for the dynamic
polarisability is derived; on the energy shell it reduces to the
conventional polarisability which is independent of the energy. We
emphasize that the present derivation is {\em non-perturbative}, i.e., it does
not make use of adiabatic or similar approximations, and is valid for energies
{\em below as well as above the three-body dissociation threshold}.Comment: 35 pages, no figures, revte
Implementation of a 6 Week Persuasive Reading and Writing Curriculum for Middle School Students
In this research project, the author presents a 6 week curricular unit that will be implemented at Soroco Middle School as a component of the Grade 7 language arts curriculum. This unit is designed to provide educators with: (a) a clear, concise method to prepare a wide variety of students for high stakes testing; (b) a deliberate approach to teach diverse students how to think critically and argue constructively; and (c) a concrete, effective method to teach a wide range of students how to use multiple writing strategies to construct persuasive paragraphs
A neutral atom quantum register
We demonstrate the realization of a quantum register using a string of single
neutral atoms which are trapped in an optical dipole trap. The atoms are
selectively and coherently manipulated in a magnetic field gradient using
microwave radiation. Our addressing scheme operates with a high spatial
resolution and qubit rotations on individual atoms are performed with 99%
contrast. In a final read-out operation we analyze each individual atomic
state. Finally, we have measured the coherence time and identified the
predominant dephasing mechanism for our register.Comment: 4 pages, 4 figure
Chemical equilibrium study at SPS 158A GeV
A detailed study of chemical freeze-out in nucleus-nucleus collisions at beam
energy 158A GeV is presented. By analyzing hadronic multiplicities within the
statistical hadronization approach, the chemical equilibration of p-p, C-C,
Si-Si and Pb-Pb systems is studied as a function of the number of participating
nucleons in the system. Additionally, Two Component statistical hadronization
model is applied to the data and is found to be able to explain the observed
strangeness hadronic phase space under-saturation.Comment: 4 pages, 3 figures to appear in the proceedings of the ''Strangeness
in Quark Matter 2004'' conferenc
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