Measurement of the fusion rate in μd 3 He

Many atomic and molecular processes may occur after a muon has been stopped in a mixture of hydrogen and helium isotopes. In particular, the muonic molecule μd 3 He can be formed. This molecule either decays or undergoes muon catalyzed fusion. Theory predicts a fusion rate much lower than the decay rate; moreover, the various theoretical predictions differ from each other by several orders of magnitude. With the experiment presented here we intend to measure the effective fusion rate via the detection of the 14.7 MeV fusion proton. A new target and gas mixing system, designed at JINR, were used in a ten-day test run at PSI. The fusion protons and products from other transfer and background reactions were measured with several different detectors (plastic scintillators, BGO, Germanium, neutron, and Silicon detectors). The formation rate of the μ d 3 He molecule and an upper limit for the effective fusion rate have been measured and are presented here.