Collisional transitions between HFS states of antiprotonic ³He in the presence of microwave radiation

Abstract

We consider collisional effects on the transitions between HFS states of $({\bar{\rm p}\,^3{\rm He}}^+)$ in the presence of microwave radiation. Cross sections and rates of collisional HFS transition, density shifts and broadening of M1 spectral lines are calculated within the approach developed previously for $({\bar{\rm p}\,^4{\rm He}}^+)$. The values averaged over thermal motion are used in the quantum master equation for the density matrix of HFS states in the microwave field. At the target density 3 × 10²⁰ cm^− 3 and T = 6 K, partial rates of the single spin-flip transition in $(\bar{{\rm p}}\,^3\mathrm{He}^+)$ are ∼1 · 10⁶ s^− 1. Effective relaxation rates by considering the kinetics are approximately twice more. At the same conditions collisional shifts of the M1 spectral lines are ≤ 4 kHz, collisional broadening of the lines is ≃ 0.5 MHz. The total width of the line J ^{− − +} → J ^+ − + at t _d  = 350 ns is 2.4 MHz allowing for collisional and Fourier broadenings. Maximum MW resonance signal in ³He is about 0.5 of that one in ⁴He.

This work was supported by the joint Russian Foundation for Basic Research - Austrian Science Foundation grant No. 09-02-91000 and by the Russian Foundation for Basic Research grant No. 10-02-01096.