Laser excitation of the 1s-hyperfine transition in muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (mu p) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with 2 x 10(-4) relative accuracy. In the proposed experiment, the mu p atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, then is quenched back to the singlet state by an inelastic collision with a H-2 molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a mu p atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by the laser bandwidth and collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where mu p is formed and the laser spectroscopy will occur.

Automated summary

The CREMA collaboration aims to measure the ground-state hyperfine splitting in muonic hydrogen with high accuracy using pulsed laser spectroscopy. They calculate the combined probability of laser excitation to the triplet state followed by collisional-induced deexcitation back to the singlet state, taking into account decoherence effects and Doppler effects. These calculations help optimize the experimental conditions and define the requirements for the laser system.