Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Results from the ULTRA experiment in the framework of the EUSO project   The detection of Cerenkov light from EAS in a delayed coincidence with
fluorescence light gives a strong signature to discriminate protons and
neutrinos in cosmic rays. For this purpose, the ULTRA experiment has been
designed with 2 detectors: a small EAS array (ETscope) and an UV optical device
including wide field (Belenos) and narrow field (UVscope) Cerenkov light
detectors. The array measures the shower size and the arrival direction of the
incoming EAS, while the UV devices, pointing both to zenith and nadir, are used
to determine the amount of direct and diffused coincident Cerenkov light. This
information, provided for different diffusing surfaces, will be used to verify
the possibility of detecting from Space the Cerenkov light produced by UHECRs
with the EUSO experiment, on board the ISS.

18
The categories of this paper are: econ
2
The categories of this paper are: math
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
1
The categories of this paper are: cs
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph