Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Discovery of the Gluon   Soon after the postulation of quarks, it was suggested that they interact via
gluons, but direct experimental evidence was lacking for over a decade. In
1976, Mary Gaillard, Graham Ross and the author suggested searching for the
gluon via 3-jet events due to gluon bremsstrahlung in $e^+ e^-$ collisions.
Following our suggestion, the gluon was discovered at DESY in 1979 by TASSO and
the other experiments at the PETRA collider.

4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin