K total cross sections and medium effects in nuclei

Abstract

The total cross sections for K+ mesons on carbon and deuterium nuclei have been measured in the momentum range 450-750 MeV/c at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The K+ meson is the least strongly interacting of hadronic probes and has a long mean free path in nuclear matter. The K+N interaction is dominated by the S[11] phase shift at low momenta and varies slowly with energy. These characteristics make the K+ an ideal tool for probing the nuclear volume to reveal nuclear medium effects. The ratio of K+-[^12]C to K+-d total cross sections has been predicted to reveal possible unconventional effects of the nuclear medium. The experimental technique was of the standard transmission type utilizing an array of concentric plastic scintillators. The targets were of solid graphite and deuterated polyethylene and were alternated with an empty target of identical geometry. Particle identification was provided with time-of-flight and Cerenkov detectors. A system of drift chambers provided beam phase space information. The measured transmission cross sections were corrected for the Coulomb interaction and then extrapolated to zero scattering angle. The resulting total cross section ratio, in agreement with previous measurements, is found to lie significantly above the possible range predicted by conventional optical model calculations. This indicates that phenomena, such as nucleon "swelling", are taking place within the nucleus which cannot be reconciled with conventional nuclear medium corrections. The data are compared with the predictions of "swelling" models and do not reproduce the predicted momentum dependence of the effect on the total cross section ratio.