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Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM, Physics, Instrumentation and Detectors, physics.ins-det
Abstract:
XENON is a direct detection dark matter project, consisting of a time
projection chamber (TPC) that uses xenon in double phase as a sensitive
detection medium. XENON100, located at the Laboratori Nazionali del Gran Sasso
(LNGS) in Italy, is one of the most sensitive experiments of its field. During
the operation of XENON100, the design and construction of the next generation
detector (of ton-scale mass) of the XENON project, XENON1T, is taking place.
XENON1T is being installed at LNGS as well. It has the goal to reduce the
background by two orders of magnitude compared to XENON100, aiming at a
sensitivity of $2 \cdot 10^{-47} \mathrm{cm}^{\mathrm{2}}$ for a WIMP mass of
50 GeV/c$^{2}$. With this goal, an active system that is able to tag muons and
their induced backgrounds is crucial. This active system will consist of a
water Cherenkov detector realized with a water volume $\sim$10 m high and
$\sim$10 m in diameter, equipped with photomultipliers of 8 inches diameter and
a reflective foil. In this paper we present the design and optimization study
for this muon veto water Cherenkov detector, which has been carried out with a
series of Monte Carlo simulations, based on the GEANT4 toolkit. This study
showed the possibility to reach very high detection efficiencies in tagging the
passage of both the muon and the shower of secondary particles coming from the
interaction of the muon in the rock: >99.5% for the former type of events
(which represent $\sim$ 1/3 of all the cases) and >70% for the latter type of
events (which represent $\sim$ 2/3 of all the cases). In view of the upgrade of
XENON1T, that will aim to an improvement in sensitivity of one order of
magnitude with a rather easy doubling of the xenon mass, the results of this
study have been verified in the upgraded geometry, obtaining the same
conclusions.
