Laser spectroscopy of light muonic atoms and the nuclear charge radii

Abstract

The energy levels of hydrogen-like atomic systems are shifted slightly by the complex structure of the nucleus, in particular by the finite size of the nucleus. These energy shifts are vastly magnified in muonic atoms and ions, i.e. the hydrogen-like systems formed by a negative muon and a nucleus. By measuring the 2S-2P energy splitting in muonic hydrogen, muonic deuterium and muonic helium, we have been able to deduce the p, d, ^33He and ^44He nuclear charge radii to an unprecedented accuracy. These radii provide benchmarks for hadron and nuclear theories, lead to precision tests of bound-state QED in regular atoms and to a better determination of the Rydberg constant.

The muX project

“…The MIDAS-based DAQ uses SIS3316 250 MSPS digitizers 3 which record all detector hits above threshold. Physics events are reconstructed offline by the analysis software.…”

“…In the past, the absolute nuclear charge radii < r 2 > 1/2 of almost all stable nuclei have been determined with a typical accuracy of 10 −4 -10 −3 by measuring the 2p − 1s transition energy [2]. More recently, the radii of the lightest nuclei were measured by the CREMA collaboration (Section 21 [3]) using laser spectroscopy on muonic atoms [4][5][6][7].…”

Cyclotron trap

“…A method was developed to extract muons from the centre of the trap to form a low-energy muon beam. This opened a path for important experiments to determine the proton radius via the Lamb shift in muonic hydrogen [16] (Section 21 [17]).…”

A theory vade mecum for PSI experiments

“…The CREMA collaboration also investigated muonic deuterium and helium 9 and determined the corresponding charge radii. Measuring the charge radii of higher Z nuclei 10 provides crucial input for potential atomic parity violation experiments.…”

“…As highlighted in the previous section, muonic atoms are sensitive to the nuclear structure. The measurement of the muonic-hydrogen Lamb shift by the CREMA collaboration 9 allowed the extraction of the proton root-mean-square charge radius with unprecedented precision. From the measured the Lamb shifts in µD, µ 3 He + and µ 4 He + the deuteron, helion and αparticle charge radii can be extracted.…”