LOW-ENERGY PROTON-PROTON SCATTERING NEAR THE INTERFERENCE MINIMUM USING A WINDOWLESS GAS-JET TARGET

In the energy region around 380 keV (lab.) and at detection angles nea r 45 degrees (lab.) the cross section of proton-proton scattering exhi bits a deep minimum, since the Coulomb amplitude and the nuclear ampli tude almost cancel each other out, resulting in a pronounced deviation from pure Mott scattering. A new set of precise data in the energy ra nge between 300 and 407 keV was recorded using the accelerator of the IKP Munster by employing a thin gas jet target with an areal density s maller than 8 x 10(14) cm(-2). For the first time p-p scattering near the interference minimum was studied under single scattering condition s using a high quality ion beam (energy spread <40 eV). Since the ener gy smearing was two orders of magnitude lower than that of the former measurements, a more detailed evaluation of the data was feasible, res ulting in differential cross sections near the minimum which are small er than published before. The measured values cannot be explained by t he interference of the Coulomb and the nuclear amplitude alone but sug gest the need for vacuum polarization or other additional effects. The position of the minimum was determined to be (382.8 +/- 0.1) keV. (C) 1997 Elsevier Science B.V.