V. Komarov

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.

a+0 (980)-resonance production in pp-->dK+K-0 reactions close to threshold.

The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46 MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected coincident dK+ pairs about 1000 events with a missing Kbar0 were identified, corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat) +/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p-wave between the deuteron and the kaon system. This is interpreted in terms of a0+(980)-resonance production.

Observations of atoms consisting of π+ and π− mesons

Abstract In the experiment 272±49 atoms consisting of π + and π + − mesons were observed. The atoms were produced in a Ta target by 70 GeV protons and π + and π − mesons were detected from the atom break-up in the same target.

Experimental estimation of the lifetime of atoms formed by π+ and π− mesons

Abstract Based on observation [L.G. Afanasyev et al., Phys. Lett. B 308 (1993) 200] of 272±49 atoms formed by π + and π − an estimation of the atom lifetime in the ground (1S) state is obtained: τ 1 = (2.9 +∞ −2.1 ) · 10 −15 s or τ 1 > 0.6·10 −15 s at 90% confidence level. Atoms were produced in inclusive p Ta interactions at 70 GeV.

Proton-nucleus interactions at 640 MeV accompanied by backward emission of energetic protons

Abstract Spectra of protons of energies between 50 and 145 MeV emitted from carbon have been measured at angles from 105° to 160° with respect to the 640 MeV proton beam. The measurements have been carried out both inclusively and in coincidence with protons emitted at forward angles up to ±40° with energies from 255 MeV to 330 MeV. This energy interval has been chosen in accordance with the kinematics of quasifree scattering on two-nucleon groups. Inclusive differential cross sections at 140° and coincidence cross sections at the angle pair (− 12°, 122°) have also been measured with Be, Al, Cu and Pb targets. The data have been compared with the predictions of several models.

Near threshold η meson production in the dd→4Heη reaction

Abstract.The dd↦4Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed.

Inclusive spectra and the angular distribution of protons emitted backwards in the interaction of 640 MeV protons with nuclei

Abstract The inclusive cross sections of protons emitted with energies from 60 to 145 MeV in the bombardment of 12C by 640 MeV protons have been measured for seven laboratory angles from 105° to 160°. Under the same conditions proton spectra have been studied at 140° by using Be, Al, Cu and Pb targets. The behaviour of the structure function Eσt−1 ·dσ/d3P at intermediate energies is discussed.

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

Determination of deuteron beam polarizations at COSY

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