S. Mikirtychyants

The neutron-proton charge-exchange amplitudes measured in the dp → ppn reaction

Abstract.The unpolarised differential cross section and the two deuteron tensor analysing powers Axx and Ayy of the

Scalar-isovector K¯ production close to threshold

\vec dp \to \{ pp\} _s n

Measurement of the absolute differential cross section of proton–proton elastic scattering at small angles

charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27GeV, data were obtained for small momentum transfers to a {pp}s system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters Cx,x and Cy,y that were carried out in the

p\vec{d} \to n\{pp\}_{s}

\vec d\vec p \to \{ pp\} _s n

Excitation of the Delta(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV

reaction at 1.2 and 2.27GeV. The values obtained for the proton analysing power Ayp also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

First experiments with the polarized internal gas target at ANKE/COSY

Inclusive K+ production in proton-proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to K+ p and K+ pi(+) correlated pairs, can all be well described using consistent values of the total cross sections for the pp -> K+ p Lambda, pp -> K+ p Sigma(0), and pp -> K+ n Sigma(+) reactions. While the resulting values for Lambda and Sigma(0) production are in good agreement with world data, our value for the total Sigma(+) production cross section, sigma (pp -> K+ n Sigma(+)) = (2.5 +/- 0.6(stat) +/- 0.4(syst)) mu b at an excess energy of epsilon = 129 MeV, could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour. (c) 2007 Elsevier B.V. All rights reserved.