A Search for Delayed Photons from Stopped Sea Level Cosmic-Ray Mesons

Abstract

If the meson disintegrates into a photon and an electron, the stopping of a meson and its subsequent decay should give rise to a delayed 50-Mev photon. Delayed coincidences were sought between the stopped meson and the photon, detected by its materialization in a Pb sheet (calculations are presented of the photon detection efficiency for various lead thicknesses and photon energies of 20, 40, and 60 Mev; the electron range-energy curves used in the calculation are also shown). In 477.4 hours, nine apparent delayed photon coincidences were found. The measured inefficiency of the anticoincidence arrangement leads us to expect five spurious delayed photon coincidences in this time, so we conclude that the number of true delayed photon coincidences is small, if not zero. If the hypothesis under test is correct, the expected number of true delayed photon coincidences, computed from the rate of delayed electron coincidences (as measured with the same geometry) and the calculated photon detecting efficiency, is of the order of 100. The negative result of this test argues not only against decay into a photon and an electron, but also shows that if meson decay leads to a neutral meson which then decays into two photons, the mean life against the latter process must be greater than about ${10}^{-10\mathrm{}}$ sec.