46 research outputs found
Electromagnetic corrections for the analysis of low energy pi-p scattering data
We calculate the electromagnetic corrections to the isospin invariant mixing
angle and to the two eigenphases for the s and p-waves for low energy pi-p
elastic and charge exchange scattering. These corrections have to be applied to
the nuclear quantities obtained from phase shift analyses of the experimental
data in order to obtain the hadronic phases. We compare our results with
earlier calculations and estimate the uncertainties in the corrections.Comment: 19 pages, 5 figures. Uses elsart.cls Accepted for publication in
Nuclear Physics
Isospin Splitting in the Baryon Octet and Decuplet
Baryon mass splittings are analyzed in terms of a simple model with general
pairwise interactions. At present, the masses are poorly known from
experiments. Improvement of these data would provide an opportunity to make a
significant test of our understanding of electromagnetic and quark-mass
contributions to hadronic masses. The problem of determining resonance masses
from scattering and production data is discussed.Comment: 9 pages, LATEX inc. 2 LATEX "pictures", CMU-HEP91-24-R9
The Goldberger-Miyazawa-Oehme sum rule revisited
The Goldberger-Miyazawa-Oehme sum rule is used to extract the pion-nucleon
coupling constant from experimental N information. Chiral perturbation
theory is exploited in relating the pionic hydrogen s-wave level shift and
width results to the appropriate scattering lengths. The deduced value for the
coupling is , where the largest source of uncertainty is
the determination of the s-wave scattering length from the atomic
level shift measurement.Comment: 4 pages, 1 figure. v2: Revised the second last paragraph of 5th
section and clarified the electromagnetic corrections (Tromborg vs.
PT). Also removed the KH80 slope from the fig.
Phase-shift analysis of low-energy elastic-scattering data
Using electromagnetic corrections previously calculated by means of a
potential model, we have made a phase-shift analysis of the
elastic-scattering data up to a pion laboratory kinetic energy of 100 MeV. The
hadronic interaction was assumed to be isospin invariant. We found that it was
possible to obtain self-consistent databases by removing very few measurements.
A pion-nucleon model was fitted to the elastic-scattering database obtained
after the removal of the outliers. The model-parameter values showed an
impressive stability when the database was subjected to different criteria for
the rejection of experiments. Our result for the pseudovector
coupling constant (in the standard form) is . The six
hadronic phase shifts up to 100 MeV are given in tabulated form. We also give
the values of the s-wave scattering lengths and the p-wave scattering volumes.
Big differences in the s-wave part of the interaction were observed when
comparing our hadronic phase shifts with those of the current GWU solution. We
demonstrate that the hadronic phase shifts obtained from the analysis of the
elastic-scattering data cannot reproduce the measurements of the
charge-exchange reaction, thus corroborating past evidence that the hadronic
interaction violates isospin invariance. Assuming the validity of the result
obtained within the framework of chiral perturbation theory, that the mass
difference between the - and the -quark has only a very small effect on
the isospin invariance of the purely hadronic interaction, the
isospin-invariance violation revealed by the data must arise from the fact that
we are dealing with a hadronic interaction which still contains residual
effects of electromagnetic origin.Comment: 43 pages, 6 figure
Low-energy Pion-nucleon Scattering
This paper contains the results of an analysis of recent low-energy
pion-nucleon scattering experiments. Obtained are phase shifts, the
pion-nucleon coupling constant and an estimate of the Sigma term.Comment: 30 pages, 11 figures, LaTe
Determination of the pion-nucleon coupling constant and scattering lengths
We critically evaluate the isovector GMO sum rule for forward pion-nucleon
scattering using the recent precision measurements of negatively charged
pion-proton and pion-deuteron scattering lengths from pionic atoms. We deduce
the charged-pion-nucleon coupling constant, with careful attention to
systematic and statistical uncertainties. This determination gives, directly
from data a pseudoscalar coupling constant of
14.11+-0.05(statistical)+-0.19(systematic) or a pseudovector one of 0.0783(11).
This value is intermediate between that of indirect methods and the direct
determination from backward neutron-proton differential scattering cross
sections. We also use the pionic atom data to deduce the coherent symmetric and
antisymmetric sums of the negatively charged pion-proton and pion-neutron
scattering lengths with high precision. The symmetric sum gives
0.0012+-0.0002(statistical)+-0.0008 (systematic) and the antisymmetric one
0.0895+-0.0003(statistical)+-0.0013(systematic), both in units of inverse
charged pion-mass. For the need of the present analysis, we improve the
theoretical description of the pion-deuteron scattering length.Comment: 27 pages, 5 figures, submitted to Phys. Rev. C, few modifications and
clarifications, no change in substance of the pape
The ontogeny of antipredator behavior: age differences in California ground squirrels (Otospermophilus beecheyi) at multiple stages of rattlesnake encounters
Newborn offspring of animals often exhibit fully functional innate antipredator behaviors, but they may also require learning or further development to acquire appropriate responses. Experience allows offspring to modify responses to specific threats and also leaves them vulnerable during the learning period. However, antipredator behaviors used at one stage of a predator encounter may compensate for deficiencies at another stage, a phenomenon that may reduce the overall risk of young that are vulnerable at one or more stages. Few studies have examined age differences in the effectiveness of antipredator behaviors across multiple stages of a predator encounter. In this study, we examined age differences in the antipredator behaviors of California ground squirrels (Otospermophilus beecheyi) during the detection, interaction, and attack stages of Pacific rattlesnake (Crotalus oreganus) encounters. Using free-ranging squirrels, we examined the ability to detect free-ranging rattlesnakes, snake-directed behaviors after discovery of a snake, and responses to simulated rattlesnake strikes. We found that age was the most important factor in snake detection, with adults being more likely to detect snakes than pups. We also found that adults performed more tail flagging (a predator-deterrent signal) toward snakes and were more likely to investigate a snake’s refuge when interacting with a hidden snake. In field experiments simulating snake strikes, adults exhibited faster reaction times than pups. Our results show that snake detection improves with age and that pups probably avoid rattlesnakes and minimize time spent in close proximity to them to compensate for their reduced reaction times to strikes