Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coupled-channel analysis of collisional effects on HFS transitions in
  antiprotonic helium atoms   Collisions of metastable antiprotonic helium with atoms of medium induce
transitions between hyperfine structure sublevels as well as shifts and
broadenings of the microwave M1 spectral lines. We consider these phenomena in
the framework of a model with scalar and tensor interactions between
antiprotonic and ordinary helium atoms. S-matrix is obtained by solving
coupled-channels equations involving 4 HFS sublevels (F=L\pm 1/2, J=F\pm 1/2)
of the nL level and relative angular momenta up to l=5 at the kinetic energy
E<25 K. The calculated spin-flip cross sections are less than elastic ones by
four orders of value in the case \Delta J=\pm 1, and by seven orders of value
in the case \Delta F=\pm 1, \Delta J=0 or \Delta J=\pm 2. The considered cross
sections reveal a resonance behaviour at very low energy (E about 1 - 4 K
depending on the model parameters). At the density N=3\times 10^{20} cm^{-3}
and T=6 K we obtain the relaxation time =160 ns, the frequency shift \Delta\nu\
= 80 kHz and the frequency broadening \gamma \lesssim 5.9 MHz for M1 spectral
lines of the favored transitions (\Delta F=\pm 1, \Delta J=\pm 1). The results
are compatible with the recent experimental data obtained by a
laser-microwave-laser resonance method. With the temperature rising up to 25 K
the rate of relaxation \lambda=1/\tau as well as shift and broadening of the M1
microwave lines are lowered by a factor 1.5 - 2 reflecting the displacement of
a mean kinetic energy from the region of resonance scattering.

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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
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The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci