1,053 research outputs found
Analysis of eta production using a generalized Lee model
We have investigated the processes N(, )N and N(, )N
close to eta threshold using a simple, nonrelativistic Lee model which has the
advantage of being analytically solvable. It is then possible to study the
Riemann sheets of the S-matrix and the behavior of its resonance poles
especially close to threshold. A theoretical simulation of the experimental
cusp effect at eta threshold leads to a characteristic distribution of poles on
the Riemann sheets. We find a pole located in the Riemann sheet that
up to now has not been discussed. It belongs to the cusp peak at eta threshold.
In addition we obtain the surprising result using the Lee model that the
resonance does not play a large role. The main features of the
experimental data can be reproduced without explicitly introducing this
resonance. Furthermore, we have also studied the reactions N(, )N
and N(, )N and find reasonable agreement between the data and
both models with and without the resonance.Comment: 17 pages LATEX including 13 Figurs, submitted to Z. Phys.
Dispersion relation formalism for virtual Compton scattering and the generalized polarizabilities of the nucleon
A dispersion relation formalism for the virtual Compton scattering (VCS)
reaction on the proton is presented, which for the first time allows a
dispersive evaluation of 4 generalized polarizabilities at a four-momentum
transfer 0.5 GeV. The dispersive integrals are calculated using
a state-of-the-art pion photo- and electroproduction analysis. The dispersion
formalism provides a new tool to analyze VCS experiments above pion threshold,
thus increasing the sensitivity to the generalized polarizabilities of the
nucleon.Comment: 4 pages, 2 figure
Cross sections for the production of fragments with Z greater than or equal to 8 by fragmentation of Z greater than or equal to 9 and less than or equal to 26 nuclei
Charge changing nuclear collisions in plastic nuclear track detectors were studied using a new experimental technique of automatic track measurement for etched tracks in plastic detectors. Partial cross sections for the production of fragments of charge Z approximately 8 were measured for projectile nuclei of charge 9 approximately Z approximately 26 in the detector material CR39 and in silver. for this purpose three independent experiments were performed using Bevalac beams. The first one was an exposure of a stack of CR39 plastic plates to 1.8 GeV/nucl. Ar-40 nuclei. The second one was an exposure of another CR39 stack of 1.7 GeV/nucl. Fe-56 projectiles. In the third experiment a mixed stack of CR39 plates and silver foils was irradiated with 1.7 GeV/nucl. Fe-56 nuclei. Thus the measurement of nuclear cross sections in a light target (CR39 = C12H18O7) and as well in a heavy target (silver) was possible
Results from the Analysis of Crystal Ball Meson Production Measurements at BNL
The Crystal Ball spectrometer, with its nearly complete angular coverage, is
an efficient detector of photon and neutron final states. While installed in
the C6 beamline of the Alternating Gradient Synchrotron (AGS) of Brookhaven
National Laboratory (BNL), this feature was used in a series of precise
measurements of reactions with all-neutral final states. Here we concentrate on
the analysis of data from the pion-induced reactions: pi- p --> gamma n, pi- p
--> pi0 n, pi- p --> eta n, and pi- p --> pi0 pi0 n.Comment: Conference contribution to MESON 2006 - Krakow, Pola
USCID fourth international conference
Presented at the Role of irrigation and drainage in a sustainable future: USCID fourth international conference on irrigation and drainage on October 3-6, 2007 in Sacramento, California.Includes bibliographical references.Centre pivot irrigation systems are known for their irrigation distribution performance potential. Unfortunately the performance analysis of centre pivot irrigation systems is often restricted to the uniformity of distribution. Depending on the characteristics of the applied rainfall, a system designed for high uniformity does not guarantee a high application efficiency once the system is in operation. A method is proposed in the present paper to analyse the average rainfall depth of application and kinetic energy delivered to the soil by individual droplets all over the machine. The method requires water distribution profiles, the distribution of droplet size and velocity along the radius of coverage for any nozzle, and pressure and height of the emitter installed on the machine. Considering the number of nozzles and the range of pressure applied, there is the need for a method calculating: the emitter maximum radius of coverage, then the rainfall distribution profile, then the droplet distribution and finally the associated kinetic energy delivery. These parameters are calculated on a new model of classical design sprayers proposed by IWT Company. These results are being integrated on a centre pivot nozzle chart design software presented in the poster session
Agnostic structural disturbances (ASDs): detecting and reducing misspecification in empirical macroeconomic models
Constructing empirical specifications for structural economic models is difficult, if not impossible. As shown in this paper, even minor misspecifications may lead to large distortions for parameter estimates and implied model properties. We propose a novel concept, namely an agnostic structural disturbance (ASD), that can be used to both detect and correct for misspecification of structural disturbances and is easy to implement. While agnostic in nature, the estimated coefficients and associated impulse response functions of the ASDs allow us to give them an economic interpretation. We adopt the methodology to the Smets–Wouters model and formulate an improved risk-premium and an improved investment-specific productivity disturbance
Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
Using the techniques of chiral effective field theories we evaluate the so
called generalized polarizabilities of the nucleon, which characterize the
structure dependent components in virtual Compton scattering (VCS) as probed in
the electron scattering reaction e N \to e' N gamma. Results are given for both
spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy
Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale
Expansion. Finally we compare our calculations with results from the pioneering
VCS experiment on the proton from Mainz.Comment: 39 pages, 12 figures, revte
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