Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lower limit on the ultra-high-energy proton-to-helium ratio from the
  measurements of the tail of $X_{\mathrm{max}}$ distribution   There are multiple techniques to determine the chemical composition of the
ultra-high-energy cosmic rays. While most of the methods are primarily
sensitive to the average atomic mass, it is challenging to discriminate between
the two lightest elements: proton and helium. In this paper, the
proton-to-helium ratio in the energy range $10^{18.0} \mbox{eV}$ to $10^{19.3}
\mbox{eV}$ is estimated using the tail of the distribution of the depth of the
shower maximum $X_{\mathrm{max}}$. Using the exponential decay scale $\Lambda$
measured by the Pierre Auger Observatory and the Telescope Array experiment we
derive the 68\%\,CL constraints on the proton-to-helium ratio
$\mathrm{p}/\mathrm{He} > 7.3 $ and $\mathrm{p}/\mathrm{He} > 0.43 $ for
$10^{18.0} < E < 10^{18.5}$ eV and $10^{18.3} < E < 10^{19.3}$ eV
correspondingly. It is shown that the result is conservative with respect to
the admixture of heavier elements. We evaluate the impact of the hadronic
interaction model uncertainty. The implications for the astrophysical models of
the origin of cosmic rays and the safety of the future colliders are discussed.

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The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg