Double Cloud-Chamber Investigation of500 meParticles in Cosmic Rays

Abstract

The Princeton double cloud chamber was used to investigate the mass spectrum of long-lived cosmic-ray particles between the $\ensuremath{\mu}$-meson and the proton masses. It was operated at two locations: (1) Echo Lake, Colorado (3250 m altitude and 42\ifmmode^\circ\else\textdegree\fi{} geomagnetic latitude); (2) Princeton, New Jersey (sea level). The upper cloud chamber operated in a magnetic field of 5500 gauss. The lower chamber contained 7 copper plates of 1.27 cm thickness each. The range of a stopping particle was between 120 and 200 g/${\mathrm{cm}}^{2}$Cu equivalent. No production layer was used. At Echo Lake a water \ifmmode \check{C}\else \v{C}\fi{}erenkov counter was included in the counter arrangement to bias against $\ensuremath{\mu}$ mesons. The mass of every stopping particle was determined from momentum and range. A measurement of the ionization by droplet counting was possible in the upper chamber. No particle of about 500 electron masses was found in either run as compared to an equivalent flux of about 1000 stopped $\ensuremath{\mu}$ mesons at Echo Lake and 1500 stopped $\ensuremath{\mu}$ mesons at Princeton. These results are in disagreement with the Alikhanian experiment.