Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Clustering of ultra-high energy cosmic ray arrival directions on medium
  scales   The two-point autocorrelation function of ultra-high energy cosmic ray
(UHECR) arrival directions has a broad maximum around 25 degrees, combining the
data with energies above $4\times 10^{19}$ eV (in the HiRes energy scale) of
the HiRes stereo, AGASA, Yakutsk and SUGAR experiments. This signal is not or
only marginally present analyzing events of a single experiment, but becomes
significant when data from several experiments are added. Both the energy
dependence of the signal and its angular scale might be interpreted as first
signatures of the large-scale structure of UHECR sources and of intervening
magnetic fields.

11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con