Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Zemach and magnetic radius of the proton from the hyperfine splitting in
  hydrogen   The current status of the determination of corrections to the hyperfine
splitting of the ground state in hydrogen is considered. Improved calculations
are provided taking into account the most recent value for the proton charge
radius. Comparing experimental data with predictions for the hyperfine
splitting, the Zemach radius of the proton is deduced to be $1.045(16)$ fm.
Employing exponential parametrizations for the electromagnetic form factors we
determine the magnetic radius of the proton to be $0.778(29)$ fm. Both values
are compared with the corresponding ones derived from the data obtained in
electron-proton scattering experiments and the data extracted from a rescaled
difference between the hyperfine splittings in hydrogen and muonium.

23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin