Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low Statistics of EHECRs   The nature of the unknown sources of ultra-high energy cosmic rays can be
revealed through the detection of the GZK feature in the cosmic ray spectrum.
The only two experiments that have probed this energy range, AGASA and HiRes,
have apparently conflicting results. HiRes measured a flux consistent with the
GZK feature while AGASA reported a larger than expected flux of so-called
Super-GZK particles. Here we emphasize that neither experiment has gathered the
statistics necessary for making a definitive measurement of the GZK cutoff. The
photo-pion production responsible for the GZK feature is stochastic for
energies around the cutoff leading to large fluctuations of the spectrum for
low statistics measurements. We show that the results from AGASA and HiRes
results are within about $ 2 \sigma$ of one another by simulating 400 spectra
for a range of input spectral indices normalized to the number of events above
$10^{19}$ eV for each experiment. If a 15% systematic correction in energy is
applied to both experiments, the agreement between the experiments improves
considerably and the best fit input spectral index becomes $\sim 2.6$ for both
data sets. Our results clearly show the need for much larger experiments such
as Auger and EUSO, that can increase the number of detected events by 2 orders
of magnitude. Only large statistics experiments can finally prove or disprove
the existence of the GZK feature in the cosmic ray spectrum.

7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom