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ATLAS - A Toroidal LHC Apparatus

Physicists at the Max Planck Institute for Physics have constructed the ATLAS particle detector together with scientists from all over the world. ATLAS is an experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN near Geneva. The LHC has a circumference of 27 km and is 100 m below the surface. The LHC began operating in 2008. In March 2010 the research program was launched, with proton-proton collisions at higher energies than any previous accelerator. Researchers from around the world use the LHC to find out more about the secrets of nature.

ATLAS measures proton-proton collisions, creating conditions similar to those prevailing shortly after the Big Bang in the early hot and dense universe. The researchers hope to find out more about the fundamental constituents of matter and their interactions. In addition to searching for the Higgs particle, they are also looking for new phenomena, such as the existence of higher dimensions in time and space and the origin of dark matter, which holds our universe together.

Members of the Max Planck Institute for Physics have particular responsibility for three specific ATLAS sub-detectors, known as the ATLAS-SCT, ATLAS-HEC and ATLAS-MDT. Furthermore they are involved in the ATLAS-Computing group.

ATLAS-SCT

SCT (© CERN)
The SemiConductor Tracker (SCT) is located in the center of the detector and thus in the immediate vicinity of the proton-proton collisions. The task of the silicon tracking detector is to measure the tracks of charged particles, and to determine their momentum based on their curve. The detector measures the trajectories of the particles with a precision of a few hundredths of a millimeters.

ATLAS-HEC

HEC (© CERN)
In order to identify the particles more precisely, it is necessary to measure their energy with the aid of calorimeters. The Hadronic Endcap Calorimeter (HEC) detects this energy, by absorbing the particles (except neutrinos and muons) completely. It consists of two end caps, each of which contains 32 pie-piece-shaped modules with 40 absorbers of 2.5 cm and 5 cm thick copper plates and 240 electrodes. The electrodes swim in liquid argon and are used to produce a signal.

ATLAS-MDT

MDT (© CERN)
Muons are particles that lose only a little energy in the detector. They pass straight through the calorimeter and are detected in the muon spectrometer that surrounds ATLAS. The detectors for muons, the Monitored Drift Tubes (MDTs) were constructed and built at the Institute.

ATLAS-Computing

ATLAS Computing Grid (© CERN)
In a single hour of operation the ATLAS detector produces about 1.1 million MB of data - the equivalent of a stack of 1500 CDs. Of the many millions of events generated per second, only a few hundred of interest are stored. This is the only way to keep the amount of data small enough to be able to manage transport, storage and processing with today's techniques. The evaluation of the data is computationally intensive and takes place worldwide on tens of thousands of computers at CERN and other data centers. Processed data, which contains only the physical essence of the recorded information, is then distributed further to about 100 smaller centers. There, it will be analyzed by all members of the ATLAS collaboration. The automated management of the data transport and computation in the many small and large data centers is known as grid computing.

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