Abstract
An experiment [CERN PS165] is described which aimed to study the interaction between a kaon and a proton by measurement of the X-ray spectrum from kaonic hydrogen in a liquid target. The spectra of exotic atoms of helium, also a liquid target, were studied first to test the apparatus. In each case the objective was to measure X-ray intensities and the strong interaction effects, namely energy shift [E] and the line broadening [T], induced by the short range nuclear force operating when a negatively charged exotic hadron reaches a low lying atomic state. The related theory and interpretation are also discussed. The results for kaonic helium, E2p = (-0.050 +/- 0.012) keV and T 2p = (0.100 +/- 0.040) keV, confirm the previous report of a disagreement with theoretical expectation. The measured 3-2 X-ray transition intensity is about 1% per atom. The results on p-helium, E 2p = (-0.012 +/- 0.014) keV and T 2p = (0.+0.040-0.) keV are in agreement with theory and contrary to the conclusions of a previous experiment (14); the absolute intensity of the 3-2 X-ray transition, measured for the first time in a liquid target, is (4.4 +/- 2.2)% per atom.