Measurement of subthreshold K+ production in pA collisions with ANKE

The magnetic spectrometer ANKE has been put into operation in spring 1998 a t the cooler synchrotron COSY-Julich. ANKE allows to momentum analyze eject iles emitted from an internal target at forward angles approximate to 0 deg rees with high angular acceptance Delta Omega approximate to 50 msr. A prim ary goal of the physics program with ANKE is the investigation of K (+) pro duction in proton-nucleus collisions at energies around and far below the f ree nucleon-nucleon threshold at T = 1.58 GeV. The measurements have been p erformed with C, Cu and Au targets at various energies in the range T = 1.0 ,..., 2.3 GeV. The major experimental challenge is that the kaon-to-backgro und ratio is as low as similar to 10(-6) at the lowest energy. Data on the target-mass dependence of the production cross sections for kaon momenta p( K+) = 150,..., 510 MeV/c at beam energies of T = 1.0 and 2.3 GeV are presen ted.