[Triumf-seminars] TRIUMF Seminar today at 14:00

postmaster@admin.triumf.ca postmaster@admin.triumf.ca
Thu, 13 May 2004 05:00:00 -0700


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Date/Time: Thu 2004-05-13 at 14:00

Location:  Auditorium          

Speaker:   Francoise Mulhauser (U. of Illinois at Urbana-Champaign (based at PSI))

Title:     Lamb Shift in Muonic Hydrogen: Toward the proton charge radius

Abstract: The proton charge radius is known only with a surprisingly low precision of about 2%. Recent reevaluation of all the electron scattering data yields a value of 0.895(18)fm. The poor knowledge of the proton charge radius restricts tests of bound-state QED to the precision level of about 6 10^{-6}, although the experimental data themselves (Lamb shift in hydrogen) have reached a precision of 2 10^{-6}. The determination of the proton charge radius with an accuracy of
10^{-3} is the main goal of our collaboration.

Our muonic hydrogen Lamb shift experiment will measure the energy difference between the 2^3S_1/2 - 2^5P_3/2 atomic levels in muonic hydrogen to a precision of 30 ppm. Very low-energy negative muons, around 20 keV, are stopped in 0.6 mbar of hydrogen gas, where, following the atomic capture and cascade, 1% of the muonic hydrogen atoms form the metastable 2S state with a lifetime of 1.3 us. A 6 um laser pulse is used to drive the 2S => 2P transition. If the laser is on resonance, the transition occurs, and the subsequent muonic deexcitation to the 1S state emits a 1.9 keV xray which is detected by Large Area Avalanche Photodiodes. The resonance frequency, and hence the Lamb shift and the proton charge radius, is determined by measuring the intensity of the x-ray fluorescence as a function of the laser wavelength.  During the last measurement period (July-December 2003) a broad range of laser frequencies was scanned and the analysis is currently under way.

Details of the experiment will be presented.

Stimulants available 15 minutes before the talk.

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