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ANTARES is a neutrino detector in the Mediterranean Sea, located 40 km off the
coast of France. It operates at a depth of about 2,5 km and consists of 12 lines
with 25 stories of photomultiplier tubes each. The detector was built to detect
neutrinos from astrophysical sources. Neutrinos pass trough the Earth and
interact with water and materials around the detector. Muons are created by this
interaction and can be detected by Cherenkov radiation. This radiation is emitted
because the muons have a velocity faster than the speed of light in water.
Gamma ray bursts (GRB) are intense flashes of light of extragalactic origin. Since
their discovery in the 1960s, GRBs have not been explained very well. The belief
is that GRBs are formed by collapsing massive stars and from neutron star
mergers. ANTARES can be used for this by detecting neutrinos, which are
believed to be created accompanying the gamma-ray production, that might
come from the GRBs. So far no neutrinos have been observed from GRBs yet, but
also current models expect a very low neutrino flux on Earth. ANTARES might
also detect signals from GRBs by observing muons created in the atmosphere
above the detector, produced by interactions of the gamma rays with the
atmosphere. This will be the focus of this project.
There are specific satellites looking out for GRBs. When a GRB is detected by one
of these satellites an alert is sent to Earth. ANTARES usually utilizes a trigger
system to filter background out of the data. When the GRB alert system provides
an alert, apart from the triggered data, also the untriggered data is stored over a
period of about two minutes.
This raw data is unbiased, because it is not triggered in any way and can contain
more signal events than the triggered data. But the raw data will also contain a
lot of background signals. The background mostly consists of bioluminescence,
which is light produced by plankton and other life in the water around the
detector and the radioactive decay of K40 in the water. Another prominent
background is muons produced in the atmosphere by interactions of cosmic rays
with the atmosphere.
The main goal of the project is to analyze the raw data from the detector, which
has so far not been used in any analysis. One of the interesting parts of this
project is also to evaluate the performance of ANTARES for particles coming
from the atmosphere above the detector, as it is designed and optimized to
detect particles coming from below, through the Earth.
In the first stage of the project, two fitting procedures to reconstruct tracks are
compared, this is done on the simulated GRB events, simulations of atmospheric
muons and on untriggered data. In this stage also performances of different
triggers implemented by ANTARES are compared. The next step is to make a
background estimation using untriggered data to calculate the sensitivity of the
ANTARES neutrino telescope to GRBs when using untriggered data and to check
whether there is an improvement in sensitivity compared to using triggered
data.