Measuring the antihydrogen Lamb shift with a relativistic antihydrogen beam

Abstract

We propose an experiment to measure the Lamb shift and fine structure ͑the intervals 2s 1/2 Ϫ2 p 1/2 and 2 p 1/2 Ϫ2p 3/2 ) in antihydrogen. A sample of 10 000 antihydrogen atoms at a momentum of 8.85 GeV/c suffices to measure the Lamb shift to 5% and the fine structure to 1%. Atomic collisions excite antihydrogen atoms to states with nϭ2; field ionization in a Lorentz-transformed laboratory magnetic field then prepares a particular nϭ2 state, and is used again to analyze that state after it is allowed to oscillate in a region of zero field. This experiment is feasible at Fermilab.

Forty years of antiprotons

“…The closure of LEAR has effectively put an end to such experiments at CERN, but the Fermilab experiment will continue for some time with attempts to measure the nϭ2 ionization cross section, the finestructure constant, and the Lamb shift for antihydrogen. These experiments, suggested by Munger et al (1994), and now proposed by Mandelkern et al (1997) and Blanford et al (1998b) are null CPT tests (albeit at low precision) to the extent that they can be repeated with hydrogen atoms recombined from protons in the same apparatus. We refer to them by the Fermilab proposal number E862.…”

“…The strong (ϳ2 ϫ10 9 V/cm) motional electric field produced by the 0.7 T magnetic field following the excitation foil splits the nϭ2 manifold into a Stark triplet. Under these conditions Blanford et al, 1998b) the field-ionization rate depends strongly on the Stark eigenstate, and the triplet can be labeled ͉⌿ L ͘, ͉⌿ M ͘ and ͉⌿ S ͘ in terms of the long, medium, and short fieldionization lifetimes of its members. These lifetimes (in the ratio 25:5:1) are such that any neutral atoms that emerge from the 30-cm-long 0.7-T magnetic field are in an almost pure ͉⌿ L ͘ state.…”

Detection of Trapped Antihydrogen

“…Also to note is the good correspondence between the simulated and measured antiproton distributions, both in position and in time 1 . This provides a validation of the simulation of Sec.…”

“…Other attractive comparative measurements include, the 2S 1/2 − 2P 1/2 Lamb shift [1] and the ground-state hyperfine structure [16][17][18]. All of these quantities have been very precisely measured for hydro- …”

“…Rejection of background events 1 The ALPHA detector is sensitive to the passage of charged particles through its silicon volume. As demonstrated in Chapter 5, the annihilation position can be determined by reconstruction of the particle tracks through the three detector layers.…”