Collisional effects on HFS transitions of antiprotonic helium

Abstract

Collisions of metastable antiprotonic helium with medium atoms induce transitions between hyperfine structure sublevels as well as shift and broadening of the microwave M1 spectral lines. We consider these effects in the framework of a simple model with scalar and tensor interactions between (pHe + ) nL and He atoms. Smatrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F = L ± 1/2, J = F ± 1/2) of the nL level and relative angular momenta up to l = 5 at the kinetic energy E 10 K. The calculated spin-flip cross sections are less than elastic ones by 4 orders of value. At the density N = 3 × 10 20 cm −3 and T = 6 K we obtain the relaxation times τ (F J → F ′ J ′ ) 160 ns, the frequency shifts of M1 spectral lines ∆ν 66 KHz for the favored transitions (∆F = ±1, ∆J = ±1) and frequency broadening of the M1 spectral lines γ/2 5.8 MHz. The results are compatible with the recent experimental data obtained by a laser-microwave-laser resonance method.Key words: antiproton, antiprotonic helium, hyperfine structure, collisional relaxation, collisional shift and broadening 34.60.+z, 32.70.Jz The discovery of antiproton longevity in helium and investigations of antiprotonic helium (pHe + ) metastable states by the method of laser resonance spectroscopy have opened a new layer of very interesting physics (see [1] and the references therein). One of the actual problems in the topics is an influence of ambient atoms on the antiprotonic states. In particular, the density shifts and broadenings of E1 spectral lines (nL → n ′ L ′ = L ± 1) were observed for laserinduced transitions. The model theoretical analysis [2] shows that qualitative

First observation of two hyperfine transitions in antiprotonic 3He

“…For p 4 He + theoretical calculations of Grigory Koren-434 man [22,23] confirmed that the density dependence 435 is very small. Also for p 3 He + theory predicts a col-436 lisional shift much smaller than our error bars [13].…”

Antiproton magnetic moment determined from the HFS of antiprotonic helium

“…A more recent calculation [27], based on mea-surements of the collisional broadening [25], predicts ∆ = −0.048 kHz/mbar which is less than the experimental precision. As a negative slope contradicts the predictions, the average of each measurement was taken but the error used was that of the extrapolation to zero density from the fit.…”

Collisional effects on the HFS transitions of antiprotonic helium

“…First two pairs are close to each other, whereas the third one, corresponding to double spin-flip, is suppressed by three orders of magnitude. All transition rates, shifts and broadenings of the spectral lines fall with temperature up to T = 10 K due to a displacement of mean kinetic energy from the resonances at very low energy [7,8]. …”

“…The only factor of importance can be a non-central part of the electrostatic interaction. In the papers [7,8] we have introduced the model potential in the form…”

“…Theoretical interpretation of the data, apart from the high-accuracy calculations for the isolated three-body system, has to include a consideration of collisional effects in the medium with the MW field present during the time between two laser pulses. In the papers [7,8] we have considered cross sections, rates of collisional transition between HFS states, shifts and broadenings of M1-transitions, using quantum close-coupling method for collisions and the model interatomic interaction involving tensor term responsible for the effects.…”