No abstract

Searches for solar axions began a decade ago when the US Brookhaven Laboratory first pointed an axion telescope at the Suna highly useful source of weakly interacting particles for fundamental research, as the solar neutrino anomaly amply demonstrates. Axions would be produced in the Sun through the scattering of photons from electric charges -the Primakoff effect -and their numbers could equal those of solar neutrinos. The idea behind the Brookhaven experiment, first proposed by Pierre Sikivie, was to put the Primakoff effect to work in reverse, using a magnetic field to catalyse the conversion of solar axions back into X-ray photons of a few kilo-electronvolts.

We report measurements of s͑u͒, A͑u͒, and polarization transfer for the 28 Si͑ p, p 0 ͒ 28 Si reaction to the 6 2 , T 1 state at 14.36 MeV initiated with 198 MeV polarized protons. Normalization of the transition strength in the distorted-wave impulse approximation (DWIA) to inelastic electron scattering overpredicts the spin-longitudinal cross section by more than a factor of 2, while the spin-transverse cross section is nearly correct and the spin-orbit cross section is underpredicted. A reduced in-medium r-meson mass reproduces some of these features, while strong relativistic mean field or Pauli blocking effects are too small. [S0031-9007(97)02543-X]

A precision measurement of spin transfer in pp elastic scattering at 197.8 MeV has been completed recently at the Indiana University Cyclotron Facility. The new data span a kinematic regime chosen specifically to maximize sensitivity to the neutral pNN coupling constant. Our results provide strong support for modern potential models of the NN interaction in which a relatively weak pion coupling (g 2 0 ഠ 13.6, f 2 0 ഠ 0.075) is employed, but disagree significantly with predictions of older models in which g 2 0 ഠ 14.4. Calculations in a one-boson-exchange framework indicate that most of these latter differences can be removed by reducing g 2 0 from 14.4 to 13.6 in these models. PACS numbers: 13.75.Cs, 21.30.Cb, 25.10. + sWhile quantum chromodynamics (QCD) is widely regarded as the underlying theory of the strong interaction, our best quantitative descriptions of most low and intermediate energy nuclear phenomena are still provided by effective theories of the interaction, in which baryons and mesons serve as efficient, collective degrees of freedom. Thus, there is great interest in determining precisely the values of the constants that appear, for example, in mesonbased models of the NN interaction. In these models, the one-pion-exchange process plays a fundamental role, dominating the long-range hadronic force, especially the tensor terms, with a strength determined primarily by the size of g 2 p , the pNN coupling constant [1]. Accurate knowledge of this coupling strength is therefore crucial for predictions of NN and pN scattering behavior and deuteron ground-state properties, or in descriptions of the NN interaction that serve as input to microscopic nuclear reaction or structure models. The strength of g 2 p also plays a critical role in testing low-energy theorems of charged pion photo-or leptoproduction, and allows one to gauge the extent to which chiral-symmetry breaking is present in the pN interaction via the Goldberger-Treiman discrepancy [2].Thus, it was quite a surprise a few years ago when new determinations of both the neutral [3] and charged [4] pion coupling constants, g 2 0 and g 2 c , based largely on global analyses of pp and pN scattering data, respectively, yielded values in striking disagreement with previous determinations and favoring much weaker couplings. The new couplings also appeared to be incompatible with the strengths required in meson-exchange models to produce the correct deuteron quadrupole moment and asymptotic D͞S state ratio [5], and with values for g 2 c recently extracted from back-angle np cross section data [6,7]. These concerns have been described at length in the literature (see, for example, [8,9]), and will not be discussed further here. It is clear, though, that many of the most contentious issues hinge on the reliability, reproducibility, or indeed the availability of data for particular sets of observables in the most critical regions of momentum transfer.Such thinking led us to investigate the sensitivity of g 2 p to various subsets of the NN database. We have sho...