Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Detection of the Characteristic Pion-Decay Signature in the Molecular
  Clouds   The $\gamma$-ray emission from molecular clouds is widely believed to have a
hadronic origin, while unequivocal evidence is still lacking. In this work, we
analyze the Fermi-LAT Pass 8 publicly available data accumulated from 2008
August 4 to 2017 June 29 and report the significant detection of a
characteristic $\pi^0$-decay feature in the $\gamma$-ray spectra of the
molecular clouds Orion A and Orion B. This detection provides a direct evidence
for the hadronic origin of their $\gamma$-ray emission.

33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th