Antiproton charge radius

The upcoming operation of the extra low energy antiprotons ring at CERN, the upgrade of the antiproton decelerator (AD), and the installation in the AD hall of an intense slow positron beam with an expected flux of $10^8{\mathrm{e}}^{+}/\mathrm{s}$ will open the possibility for new experiments with antihydrogen ($\overline{\mathrm{H}}$). Here we propose a scheme to measure the Lamb shift of $\overline{\mathrm{H}}$. For four months of data taking, we anticipate an uncertainty of 100 ppm. This will provide a test of $CPT$ and the first determination of the antiproton charge radius at the level of 10%.

Figure 1

Sensitivity as a test of $CPT$ for different systems and projected accuracy for antihydrogen experiments including the Lamb shift measurement proposed here (solid line) and sensitivity if a relative accuracy as for the matter counterpart could be achieved (dotted line). This figure was adapted from [20].

Figure 2

Scheme for the production of the metastable 2S $\overline{\mathrm{H}}$ beam.

Figure 3

Scheme of the proposed experimental setup for the measurement of the $\overline{\mathrm{H}}$ Lamb shift.

Figure 4

Calculated $\overline{\mathrm{H}}(2\mathrm{S})$ atom yield per number of Ps and antiprotons.

Figure 5

Sketch of the 2S and 2P hyperfine levels.