Freiburg 1999 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 26: Elektromagnetische und hadronische Proben V

HK 26.4: Gruppenbericht

Dienstag, 23. März 1999, 17:15–17:45, C

Study of subthreshold K⁺-production at ANKE — •M. Büscher — Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich

The spectrometer ANKE for the study of ejectiles from proton-induced reactions at internal targets in the cooler synchrotron COSY-Jülich consists of three dipole magnets. It was installed in one of the straight sections of the accelerator in May 1998 and imposes a closed orbit bump on the circulating beam. Thus it affects the accelerating procedure because of eddy currents during ramping and high-multipole components of the magnetic fields. The procedures to achieve acceleration up to the highest energies of COSY with beam intensities of up to 4·10¹⁰ per filling were developed during beam times in May and July 1998. The detectors at ANKE, the electronics and data acquisition system were tested and optimized with proton and pion ejectiles from proton-induced reactions in carbon and polyethylene strip targets of typically 2 mm by 20 mm and 60 µg/ cm² thickness. For the calibration of the system, pions from the two-body reaction pp→dπ⁺ were used at 15 different beam energies. After the commissioning phase first experiments were performed.

Among the first goals of the research program at ANKE is the investigation of nuclear medium effects on elementary processes through measurements of the K⁺-production in proton-nucleus collisions at projectile energies below the free NN-threshold at 1.58 GeV. The experiments aim at the understanding of the reaction mechanisms and the eludication of cooperative effects of the nucleons inside the nucleus which allow subthreshold production of kaons. Measured total cross sections[1] do not provide unambiguous information in this respect and further data are needed. Momentum spectra of K⁺-mesons emitted under 0^∘ with respect to the circulating beam were measured after pC interactions at projectile energies of 2.3, 1.8, 1.5 and 1.2 GeV. It is planned to extend these measurements to detailed studies of K⁺-momentum spectra at 1.0 GeV and to detect also light ejectiles like deuterons which are emitted in coincidence with the kaons. The results of the ANKE studies complement the data from SATURNE[2] and CELSIUS[3].

[1] V. Koptev et al., JETP 67 (1988) 2177

[2] M. Debowski et al., Z. Phys. A356 (1996) 313

[3] A. Badalà et al., Phys. Rev. Letters 80 (1998) 4863

Supported by: BMBF, DFG, Verbundforschung, WTZ, State of North Rhine-Westphalia, INTAS, Polish Committee for Scientific Research, RFFI, RFNP, Russian Academy of Sciences, Russian Ministry of Sciences