Direct observation of the decay of beauty particles into charm particles

Abstract The associated production of a pair of beauty particles B − and B 0 by a 350 GeV π − interaction has been observed in an emulsion target inserted in an array of silicon microstrip detectors. Both beauty particles decay into charm particles, both of which are also observed to decay in the emulsion. Two negative muons were identified and their momenta measured in a large muon spectrometer. One muon has a p T of 1.9 GeV/ c and is associated with a beauty particle decay. The other, with a p T of 0.45 GeV/ c is associated with a charm particle decay. The flight times of the two beauty particles are respectively (0.8 ± 0.1) × 10 −13 s and (5 +2 −1 ) × 10 −13 s. Alternative interpretations of this event have negligible probability.