Measurement of low energy K+ total cross sections on N=Z nuclei.

Abstract

The total cross sections for ${\mathit{K}}^{+}$ on deuterium, $^{6}\mathrm{Li}$, $^{12}\mathrm{C}$, $^{28}\mathrm{Si}$, and $^{40}\mathrm{Ca}$ have been measured at four-momenta in the range of 480--714 MeV/c. The experimental technique was of the standard transmission type. Because of its long mean free path in nuclear matter at low energies the ${\mathit{K}}^{+}$ can be expected to probe the entire volume of the nucleus. Indeed we found that, to better than 10% \ensuremath{\sigma}(${\mathit{K}}^{+}$A)=A\ensuremath{\sigma}(${\mathit{K}}^{+}$N) up to A=40. This feature was used to study more delicate effects of the nuclear medium. Special emphasis was placed on measuring the total cross section ratios of ${\mathit{K}}^{+}$A to ${\mathit{K}}^{+}$ D with a precision of \ensuremath{\le}2%. This ratio is a good measure of nuclear medium effects because many experimental as well as theoretical systematic uncertainties cancel in the ratio. We discuss the medium dependence as a function of A. The data do not agree with calculations which include only conventional medium effects. This points towards the need of unconventional nuclear medium effects such as partial quark deconfinement, mass rescaling of nuclear pionic fields or pion excess in nuclei. Thus far only calculations based on unconventional medium effects for $^{12}\mathrm{C}$ exist. Calculations for the other nuclei are needed before quantitative conclusions can be drawn.