2,500 research outputs found
System study of the carbon dioxide observational platform system (CO-OPS): Project overview
The resulting options from a system study for a near-space, geo-stationary, observational monitoring platform system for use in the Department of Energy's (DOE) National Carbon Dioxide Observational Platform System (CO-OPS) on the greenhouse effect are discussed. CO-OPS is being designed to operate continuously for periods of up to 3 months in quasi-fixed position over most global regional targets of interest and could make horizon observations over a land-sea area of circular diameter up to about 600 to 800 statute miles. This affords the scientific and engineering community a low-cost means of operating their payloads for monitoring the regional parameters they deem relevant to their investigations of the carbon dioxide greenhouse effect at one-tenth the cost of most currently utilized comparable remote sensing techniques
Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region
Differential cross sections for the process gn-->pi-p have been extracted
from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction
effects, using a diagrammatic technique taking into account the NN and piN
final-state interaction amplitudes. Results are compared to previous
measurements of the inverse process, pi-p--> ng, and recent multipole analyses.Comment: 6 pages, 4 figures. v2: Further clarifications and minor changes. A
new figure inserte
On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
We discuss the procedure of extracting the photoproduction cross section for
neutral pseudoscalar mesons off neutrons from deuteron data. The main statement
is that the final-state interaction (FSI) corrections for the proton and
neutron target are in general not equal, but for pi0 production there are
special cases were they have to be identical and there are large regions in the
parameter space of incident photon energy and pion polar angle, \theta^*, where
they happen to be quite similar. The corrections for both target nucleons are
practically identical for production in the energy range of the
Delta(1232)3/2+ resonance due to the specific isospin structure of this
excitation. Also above the -isobar range large differences between
proton and neutron correction factors are only predicted for extreme forward
angles ( < 20 deg), but the results are similar for larger angles.
Numerical results for the gp-->pi0p and gn-->pi0n correction factors are
discussed. Also the model description for the available data on the
differential gd-->pi0pn cross sections are given.Comment: 16 pages, 5 figures; v2 fixed several minor typo
Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects
The incoherent pion photoproduction reaction gd-->pi-pp is considered
theoretically in a wide energy region Eth =< Eg =< 2700 MeV. The model applied
contains the impulse approximation as well as the NN- and piN-FSI amplitudes.
The aim of the paper is to study a reliable way for getting the information on
elementary gn-->pi-p reaction cross section beyond the impulse approximation
for gd-->pi-pp. For the elementary gN-->piN, NN-->NN, and piN-->piN amplitudes,
the results of the GW DAC are used. There are no additional theoretical
constraints. The calculated cross section dSigma/dOmega(gd->pi-pp) are compared
with existing data. The procedure used to extract information on the
differential cross section dSigma/dOmega(gn-->pi-p) on the neutron from the
deuteron data using the FSI correction factor R is discussed. The calculations
for R versus pi-p CM angle \theta_1 of the outgoing pion are performed at
different photon-beam energies with kinematical cuts for "quasi-free" process
gn-->pi-p. The results show a sizeable FSI effect R \neq 1 from S-wave part of
pp-FSI at small angles close to \theta_1 ~ 0: this region narrows as the photon
energy increases. At larger angles, the effect is small (|R-1|<<1) and agrees
with estimations of FSI in the Glauber approach.Comment: 28 pages, 5 figures, 1 tabl
Parameterization dependence of T matrix poles and eigenphases from a fit to piN elastic scattering data
We compare fits to piN elastic scattering data, based on a Chew-Mandelstam
K-matrix formalism. Resonances, characterized by T-matrix poles, are compared
in fits generated with and without explicit Chew-Mandelstam K-matrix poles.
Diagonalization of the S matrix yields the eigenphase representation. While the
eigenphases can vary significantly for the different parameterizations, the
locations of most T-matrix poles are relatively stable.Comment: 6 pages, 3 figures, 1 tabl
Extended Partial-Wave Analysis of piN Scattering Data
We present results from a comprehensive partial-wave analysis of pi+-p
elastic scattering and charge-exchange data, covering the region from threshold
to 2.6 GeV in the lab pion kinetic energy, employing a coupled-channel
formalism to simultaneously fit pi-p-->eta n data to 0.8 GeV. Our main result,
solution SP06, utilizes a complete set of forward and fixed-t dispersion
relation constraints applied to the piN elastic amplitude. The results of these
analyses are compared with previous solutions in terms of their resonance
spectra and preferred values for couplings and low-energy parameters.Comment: 21 pages, 11 figure
Ratios of Elastic Scattering of Pions from 3H and 3He
We have measured the elastic-scattering ratios of normalized yields for
charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we
completed the angular distribution begun with our earlier measurements, adding
six data points in the angular range of 119 deg to 169 deg in the pi-nucleus
center of mass. We also measured an excitation function with data points at
142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle
for each energy between 160 deg and 170 deg in the pi-nucleus center of mass.
This excitation function corresponds to the energies of our forward-hemisphere
studies. The data, taken as a whole, show an apparent role reversal of the two
charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data >
100 deg we observe a strong dependence on the four-momentum transfer squared
(-t) for all of the ratios regardless of pion energy or scattering angle, and
we find that the superratio R data match very well with calculations based on
the forward-hemisphere data that predicts the value of the difference between
the even-nucleon radii of 3H and 3He. Comparisons are also made with recent
calculations incorporating different wave functions and double scattering
models.Comment: RevTex 8pages, 12 figure file
Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production
We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian
width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The
observed structure may be due to the interference between a strange (or
anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L)
photoproduction leading to the same final state. The statistical significance
of the observed excess of events estimated as the log likelihood ratio of the
resonant signal+background hypothesis and the phi-production based background
only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1
table added, revise
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