Laterally Separated Muons from Cosmic Ray Air Showers Measured with the ICECUBE Neutrino Observatory
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Cosmic rays enter the Earth’s atmosphere with energies up to 1020 eV, producing extended air showers, which contain up to billions of secondary particles that
can be detected on the ground. Inside these showers, hadrons with large transverse
momentum may be produced, which subsequently decay into muons, also
carrying large transverse momentum. These muons separate from the shower
core while traveling to the ground, producing lateral separations from the core
up to several hundred meters. Together with the dense muon core bundle, they
produce distinctive double-track signatures in the IceCube Neutrino Observatory.
The corresponding lateral separation distributions are a measure of the
underlying transverse momentum of hadrons, and therefore yield important
information on hadron production during the air shower development.
In this work, the lateral separation of atmospheric muons, between 135m
and approximately 450 m, is measured using three years of IceCube data, taken
between May 2012 and May 2015. A dedicated Monte Carlo for the simulation
of laterally separated muons from air showers is presented. This is used to
develop selection criteria in order to isolate the events of interest from IceCube
data. In addition, a specific double-track reconstruction is introduced, which
enables a precise measurement of the lateral separation and arrival direction
of muons. Using existing energy estimation methods, which are optimized for
the reconstruction of this class of events, the first primary energy dependent
analysis of the lateral separation distribution of muons far from the shower core
is performed.
After applying all selection criteria, 80951 events are left with an effective
lifetime of 960 days. The resulting lateral separation distributions are studied
with emphasis on the angular arrival directions and the transverse momentum
of muons, which is estimated based on Monte Carlo simulations. In addition,
the sensitivity of laterally separated muons on the mass composition of cosmic
ray nuclei and the seasonal variations of the resulting muon fluxes over three
years are studied.
Finally, the prospects for a search of double-track signatures, produced by
exotic particles in cosmic ray air showers, which are predicted by theories
beyond the standard model, are discussed. It is shown that, considering recent
constraints on existing theoretical models, such as supersymmetry, the expected
fluxes are below 10-3 events per year. Hence, it is concluded that the observation of exotic double-tracks from air showers, using existing neutrino telescopes, is
not feasible.