Search for 2S-state metastability in muonic helium at 40 atm

A search was made for photons from the two-photon deexcitation of the 2S state of muonic He by measuring the time and energy distributions of delayed photons emitted when negative muons were stopped in gaseous He at room temperature. An upper limit of 46 +- 1 ns was obtained for the lifetime of this state at 40 atm, in disagreement with earlier measurements. Prompt K-series muonic x rays were also measured at pressures between 0.5 and 40 atm, and the x-ray intensity ratios were used to deduce initial 2S-state populations