Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Blast from the past: Constraints on the dark sector from the BEBC WA66
  beam dump experiment   We derive limits on millicharged dark states, as well as particles with
electric or magnetic dipole moments, from the number of observed forward
electron scattering events at the Big European Bubble Chamber in the 1982
CERN-WA-066 beam dump experiment. The dark states are produced by the 400 GeV
proton beam primarily through the decays of mesons produced in the beam dump,
and the lack of excess events places bounds extending up to GeV masses. These
improve on bounds from all other experiments, in particular CHARM II.

22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat