- Conference date: 5-11 October 2000
- Location: Trieste (Itlay)
A measurement of the Lamb shift ( energy difference) in muonic hydrogen is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the Lamb shift with 30 ppm precision and to deduce the root mean square (rms) proton charge radius with relative accuracy, 20 times more precise than presently known. The experiment is based on the availability of long-lived metastable muonic hydrogen atoms in the state which has been investigated in a recent series of experiments at PSI. From the low-energy part of the initial kinetic energy distribution of atoms we determined the fraction of long-lived to be ∼1.5% for gas pressures between 1 and 64 hPa. Another analysis involving with a kinetic energy of 0.9 keV originating from quenching of thermalized via the resonant process gives the same result. This is the first direct observation of long-lived atoms. The realization of the μp Lamb shift experiment involves a new low-energy negative muon beam with entrance detectors for keV-muons, a xenon gas-proportional-scintillation-chamber (GPSC) read out by a microstrip-gas-chamber (MSGC) for the detection of 2 keV X-rays, and a randomly triggered 3-stage laser system providing 0.5 mJ, 7 ns laser pulses at 6.02 μm wavelength.
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