Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Study of two-photon production process in proton-proton collisions at
  216 MeV   The energy spectrum for high energy $\gamma$-rays ($E_\gamma \geq 10$ MeV)
from the process $pp \to \gamma \gamma X$ emitted at $90^0$ in the laboratory
frame has been measured at 216 MeV. The resulting photon energy spectrum
extracted from $\gamma-\gamma$ coincidence events consists of a narrow peak
(5.3$\sigma$) at a photon energy of about 24 MeV and a relatively broad peak
(3.5$\sigma$) in the energy range of (50 - 70) MeV. This behavior of the photon
energy spectrum is interpreted as a signature of the exotic dibaryon resonance
$d^\star_1$ with a mass of about 1956 MeV which is assumed to be formed in the
radiative process $pp \to \gamma d^\star_1$ followed by its electromagnetic
decay via the $d^\star_1 \to pp \gamma$ mode. The experimental spectrum is
compared with those obtained by means of Monte Carlo simulations.

19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc