We consider the effect of an exotic S=+1 \(\Theta^+\) resonance on the scattering of neutral kaons off protons. Explicit results are presented for the \(K^0_L p\) total cross sections.
Phys.Rev.C52:2246-2249,1995 We reexamine Chew's method for extracting the $\pi NN$ coupling constant from
np differential cross section measurements. Values for this coupling are
extracted below 350 ...MeV, in the potential model region, and up to 1 GeV. The
analyses to 1~GeV have utilized 55 data sets. We compare these results to those
obtained via $\chi^2$ mapping techniques. We find that these two methods give
consistent results which are in agreement with previous Nijmegen
determinations.
PiN Newslett.15:118-122,1999 A new result for the nucleon sigma term from an updated pion-nucleon
partial-wave and dispersion relation analysis of the Virginia Polytechnic
Institute (now George ...Washington University) group is discussed. Using a method
similar to that of Gasser, Leutwyler, Locher, and Sainio, we obtain Sigma=90
+/- 8 MeV (preliminary), in disagreement with the canonical result 64 +/- 8
MeV, but consistent with expectations based on new information on the $\pi$NN
coupling constant, pionic atoms, and the Delta resonance width.
We present results from a comprehensive partial-wave analysis of pi+-p elastic scattering and charge-exchange data, covering the region from threshold to 2.1 GeV in the lab pion kinetic energy, ...employing a coupled-channel formalism to simultaneously fit pi-p\to\eta n data to 0.8 GeV. Our main result, solution FA02, utilizes a complete set of forward and fixed-t dispersion relation constraints, from threshold to 1 GeV, and from t = 0 to -0.4 (GeV/c)^2, applied to the piN elastic amplitude. A large number of systematic checks have been performed, including fits with no charge-exchange data and other database changes, fits with few or no dispersion relation constraints, and changes to the Coulomb correction scheme. We have also reexamined methods used to extract Breit-Wigner resonance parameters. The quality of fit to both data and dispersion relation constraints is superior to our earlier work. 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, including the piNN coupling constant.
Given presently known empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F partners, paying special attention to the nonstrange member of the ...antidecuplet N*. The modified PWA analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases the N* should be highly inelastic. The theoretical analysis, based on the soliton picture and assumption of Gamma(Theta+) < 5 MeV, shows that most probably Gamma(N*) < 30 MeV. Similar analysis for Xi3/2 predicts its width to be not more than about 10 MeV. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons.
Phys.Rev.C66:054007,2002 We discuss the experimental and theoretical status of charge-symmetry
violation (CSV) in the elastic scattering of pi+ and pi- on 3H and 3He.
Analysis of the experimental ...data for the ratios r1, r2, and R at Tpi = 142,
180, 220, and 256 MeV provides evidence for the presence of CSV. We describe
pion scattering from the three-nucleon system in terms of single- and
double-scattering amplitudes. External and internal Coulomb interactions as
well as the Delta-mass splitting are taken into account as sources of CSV.
Reasonable agreement between our theoretical calculations and the experimental
data is obtained for Tpi = 180, 220, and 256 MeV. For these energies, it is
found that the Delta-mass splitting and the internal Coulomb interaction are
the most important contributions for CSV in the three-nucleon system. The CSV
effects are rather sensitive to the choice of pion-nuclear scattering
mechanisms, but at the same time, our theoretical predictions are much less
sensitive to the choice of the nuclear wave function. It is found, however,
that data for r2 and R at Tpi = 142 MeV do not agree with the predictions of
our model, which may indicate that there are additional mechanisms for CSV
which are important only at lower energies.
PiN Newslett. 15 (1999) 171-175; Phys.Scripta T87 (2000) 65-70 Our extraction of the pion-nucleon coupling constant from \pi p elastic
scattering data is outlined. A partial wave analysis (T_{\pi} < ...2100 MeV) is
performed simultaneously with a fixed-t dispersion relation analysis (T_{\pi} <
800 MeV). The \pi NN coupling constant g^2/4\pi is searched to find the best
fit. The result 13.73 \pm 0.01 \pm 0.07 (first error statistical, second
systematic) is found to be insensitive to database changes and Coulomb barrier
corrections. This value satisfies important elements of low energy QCD like the
Goldberger-Treiman discrepancy, the Dashen-Weinstein sum rule, and chiral
perturbation theory predictions of threshold pion photoproduction.
Phys.Scripta T87:62-64,2000 We summarize results obtained in our studies of the pion-nucleon coupling
constant. Several different techniques have been applied to pi-N and NN elastic
scattering data, ...and the existing database for single-pion photoproduction. The
most reliable determination comes from pi-N elastic scattering. The sensitivity
in this reaction was found to be greater, by at least a factor of 3, when
compared with analyses of NN elastic scattering or single-pion photoproduction.
Experiments that study the hadronic and electromagnetic production of the pseudoscalar mesons -- pions, etas and kaons, contribute to our knowledge of the properties of baryon and hyperon resonances. ...Fixed-target programs at hadronic facilities such as BNL-AGS have been phased out. However, the availability of modern experimental facilities with pseudo-monochromatic or tagged medium-energy photon beams at GRAAL, SPring-8, Bonn, Mainz, and Jefferson Lab, together with LEGS, Max-Lab, and HIGS at lower energies, are beginning to produce high-quality results. These new data have smaller statistical uncertainties and better understood systematic uncertainties, than those obtained at the older bremsstrahlung facilities, for measurements of differential and integrated cross sections, as well as polarization and asymmetry. Experimental results are compared with the predictions of QCD-based approaches, such as the lattice-gauge calculations of baryon properties, and Chiral Perturbation Theory applied to threshold photoproduction, and are essential to the performance of Partial-Wave Analyses (PWA). These PWA studies are less model dependent than in the past, and are used in coupled-channels calculations that incorporate unitarity dynamically, and combine results from hadronic reaction channels with electromagnetic processes. This approach is necessary to extract resonance properties and may lead to the discovery of the "missing resonances" predicted by a number of different QCD-inspired calculations. We discuss recent experimental and phenomenological results for single and double pseudoscalar meson hadronic and photoproduction channels with emphasis on the JLab Hall B and the BNL/AGS Crystal Ball programs.
Differential cross sections for the reaction \(\gamma p \to p \pi^0\) have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.675 to 2.875 ...GeV. The results reported here possess greater accuracy in the absolute normalization than previous measurements. They disagree with recent CB-ELSA measurements for the process at forward scattering angles. Agreement with the SAID and MAID fits is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been extended to 3 GeV. Resonance couplings have been extracted and compared to previous determinations.
