First we present a brief overview of the contemporary state of the High-energy Physics, with
the emphasis put on the validation of the Standard
Model. We will mention searches for Higgs boson(s), several production and
detection mechanisms, and make a quick overview of the theories
Beyond the Standard Model. Then we will describe the todays most promising
particle collider LHC and mainly the state-of-the-art detector ATLAS
and its subsystems; the special focus will be on the Pixel detector. Next
we mention the ATLAS offline computing. The principles and use of the
Athena - ATLAS offline software framework will be discussed. Finally the
speaker's own research activity will be described: the effect
of cosmic rays on the Pixel detector. This is done using Geant4 simulation
within Athena. All the software tools will be introduced and described, the
preliminary results will be then used to discuss their efficiency. Subsequently,
the cosmic rate and the distribution of hits and energy will be estimated.
At the closing, we will present an outlook how to improve the cosmic rate estimate
by folding in the trigger efficiency simulation.