Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precise Measurement of the Absolute Yield of Fluorescence Photons in
  Atmospheric Gases   We have performed a measurement of the absolute yield of fluorescence photons
at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by
the use of Cherenkov radiation as a reference calibration light source. A
cross-check was performed by an independent calibration using a laser light
source. A significant improvement on the energy scale uncertainty of Ultra-High
Energy Cosmic Rays is expected.

20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin