A. Kacharava

ANKE, a new facility for medium energy hadron physics at COSY-Jülich

Abstract ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Julich (FZ-Julich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.

Lineshape of the Λ(1405) hyperon measured through its Σ0π0 decay

The pp --> pK(+)Y(0) reaction has been studied for hyperon masses m (Y-0) <= 1540 MeV/c(2) at COSY-Julich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Lambda and Sigma(0) hyperons as well as the Sigma(0)(1385) and Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well separated, though with limited statistics. The shape and position of the Lambda(1405) distribution, reconstructed cleanly in the Sigma(0)pi(0) channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Lambda( 1405) to be a two-state resonance

Is there an ηHe3 quasi-bound state?

Abstract The observed variation of the total cross section for the d p → He 3 η reaction near threshold means that the magnitude of the s-wave amplitude falls very rapidly with the η centre-of-mass momentum. It is shown here that recent measurements of the momentum dependence of the angular distribution imply a strong variation also in the phase of this amplitude. Such a behaviour is that expected from a quasi-bound or virtual η He 3 state. The interpretation can be investigated further through measurements of the deuteron or proton analysing powers and/or spin-correlations.

Proton-induced deuteron breakup at GeV energies with forward emission of a fast proton pair

Abstract A study of the deuteron breakup reaction pd →( pp ) n with forward emission of a fast proton pair with small excitation energy E pp T p =xa00.6,xa00.7,xa00.8,xa00.95,xa01.35 and 1.9xa0GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to 8° over the cm polar angle of the total momentum of the pp pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic pd → dp scattering, the results are compared to calculations based on a theoretical model previously applied to the pd → dp process.

Identification of K+-mesons from subthreshold pA collisions with ANKE at COSY-Jülich

Abstract The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Julich in spring 1998. An initial scientific goal is to study K + -production in pA collisions at subthreshold energies far below the free NN-threshold at T p =1.58xa0GeV. This requires the identification of K + -mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2 σ/ d Ω d p for deep subthreshold K + production at beam energies down to T p =1.0xa0GeV.

Precision study of the dp -> He-3 eta reaction for excess energies between 20 and 60 MeV

The differential and total cross sections for the dp -> He-3 eta reaction have been measured at COSY-ANKE at excess energies of 19.5, 39.4, and 59.4 MeV over the full angular range. The results are in line with trends apparent from the detailed near-threshold studies and also largely agree with those from CELSIUS, though the present data have much better angular coverage near the forward and backward directions, thus allowing firmer conclusions to be drawn. While at 19.5 MeV the results can be described in terms of s- and p-wave production, by 59.4 MeV higher partial waves are required. Including the 19.5 MeV point together with the near-threshold data in a global s- and p-wave fit gives a poorer overall description of the data though the position of the pole in the eta He-3 scattering amplitude, corresponding to the quasibound or virtual state, is hardly changed.

Polarizing a Stored Proton Beam by Spin-Flip?

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin-flip cross section in low-energy electron–proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.

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

Study of ω-meson production in pp collisions at ANKE

vec dp to { pp} _s n