Zero degrees centigrade - or the d + d → α + 2π reaction in celsius

A simple spectrometer has been built for charged particles emitted in forward directions from the cluster-jet target in CELSIUS. It consists of a ΔE-E telescope of high-purity germanium which can be inserted into the CELSIUS ring in the bend following the target straight section. We study the reaction d+d→α+2π close to threshold as a means of investigating the production and rescattering of isospin, I=0, pion pairs at low energy. The double-differential cross section for the production of alpha particles in forward directions is measured. In June of 1992 an exploratory measurement using a 570 MeV deuteron beam was made. With an integrated luminosity of 8.8x1033 cm-2, 10 events were identified as due to the α+2π reaction. A second experiment was performed in December with an increased luminosity. A short description is given of the experiments including the performance of the spectrometer, and some preliminary results are presented. (orig.)