Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Laser spectroscopy of the $^2S_{1/2} - ^2P_{1/2}$, $^2P_{3/2}$
  transitions in stored and cooled relativistic C$^{3+}$ ions   The $^2S_{1/2} - ^2P_{1/2}$ and $^2S_{1/2} - ^2P_{3/2}$ transitions in
Li-like carbon ions stored and cooled at a velocity of $\beta \approx 0.47$ in
the Experimental Storage Ring (ESR) at the GSI Helmholtz Centre in Darmstadt
have been investigated in a laser spectroscopy experiment. Resonance
wavelengths were obtained using a new continuous-wave UV laser system and a
novel extreme UV (XUV) detection system to detect forward emitted fluorescence
photons. The results obtained for the two transitions are compared to existing
experimental and theoretical data. A discrepancy found in an earlier laser
spectroscopy measurement at the ESR with results from plasma spectroscopy and
interferometry has been resolved and agreement between experiment and theory is
confirmed.

35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin