Search for long-lived heavy particles in cosmic-ray events at energies above several thousand GeV

Summary  Two experiments are described, designed to search for heavy, long-lived particles (mass ≳ 5 GeV/c2, lifetime ≳10−6 s) with strong and/or electromagnetic interactions. If such particles exist, they may be expected to occur in air showers and some should arrive at sea level, delayed with respect to the bulk of air shower particles, yet carrying a large amount of energy. Our apparatus was constructed so as to register particles delayed from 20 to 520 ns with respect to an air shower and capable of penetrating a large amount of matter (ranging from 1600 to 3600 g/cm2). In the first experiment the particles had to be at least singly charged or to interact in 1.6 tons of detector. In the second experiment it was required that the particles had a reasonably large cross-section for pion production. The result of the experiments is negative; upper limits for the occurrence of signals due to delayed energetic particles lie between 10−10 and 3·10−10 cm−2 s−1. Upper limits on the production cross-section of such particles can be obtained only by assuming a particular model for their production and propagation. We can infer however that, if particles of this kind exist, their production cross-section must be small even in the energy range from 10000 to 50000 GeV. A particular model, which is discussed in Appendix III, yields upper limits in the region of 10 µb for the production of particles which are about ten times as heavy as nucleons.