Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Upper limit on the diffuse flux of UHE tau neutrinos from the Pierre
  Auger Observatory   The surface detector array of the Pierre Auger Observatory is sensitive to
Earth-skimming tau-neutrinos $\nu_\tau$ that interact in the Earth's crust. Tau
leptons from $\nu_\tau$ charged-current interactions can emerge and decay in
the atmosphere to produce a nearly horizontal shower with a significant
electromagnetic component. The data collected between 1 January 2004 and 31
August 2007 is used to place an upper limit on the diffuse flux of $\nu_\tau$
at EeV energies. Assuming an $E_\nu^{-2}$ differential energy spectrum the
limit set at 90 % C.L. is $E_\nu^{2} \mathrm{d}N_{\nu_\tau}/\mathrm{d}E_{\nu} <
1.3 \times 10^{-7}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ in the energy range
$2\times10^{17} \mathrm{eV} < E_\nu < 2\times10^{19}$ eV.

7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph