Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lepton universality test in the photoproduction of $e^- e^+$ versus
  $\mu^- \mu^+$ pairs on a proton target   In view of the significantly different proton charge radius extracted from
muonic hydrogen Lamb shift measurements as compared to electronic hydrogen
spectroscopy or electron scattering experiments, we study in this work the
photoproduction of a lepton pair on a proton target in the limit of very small
momentum transfer as a way to provide a test of the lepton universality when
extracting the proton charge form factor. By detecting the recoiling proton in
the $\gamma p \to l^- l^+ p$ reaction, we show that a measurement of a ratio of
$e^-e^+ + \mu^-\mu^+$ over $e^-e^+$ cross sections with a relative precision of
around 2%, would allow for a test to distinguish between the two different
proton charge radii currently extracted from muonic and electronic observables.

31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con