Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Anomalous Internal Pair Creation in $^8$Be: A Possible
  Signature of a Light, Neutral Boson   Electron-positron angular correlations were measured for the isovector
magnetic dipole 17.6 MeV state ($J^\pi=1^+$, $T=1$) $\rightarrow$ ground state
($J^\pi=0^+$, $T=0$) and the isoscalar magnetic dipole 18.15 MeV ($J^\pi=1^+$,
$T=0$) state $\rightarrow$ ground state transitions in $^{8}$Be. Significant
deviation from the internal pair creation was observed at large angles in the
angular correlation for the isoscalar transition with a confidence level of $>
5\sigma$. This observation might indicate that, in an intermediate step, a
neutral isoscalar particle with a mass of 16.70$\pm0.35 $ (stat)$\pm 0.5 $
(sys) MeV$/c^2$ and $J^\pi = 1^+$ was created.

12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con