ATLAS experiment

  • ATLAS
  • CMS
  • LHCb
  • ALICE
  • MoEDAL
  • Linear accelerators for protons (p ) or lead nuclei (Pb)
  • Proton Synchrotron Booster (PSB )
  • Proton Synchrotron (PS )
  • Super Proton Synchrotron (SPS )

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ATLAS is a particle detector at the Large Hadron Collider ( LHC), a particle accelerator at the European Nuclear Research CERN. ATLAS A Toroidal LHC originally stood for apparatus, but is now only used as a proper name. Among other things, with ATLAS first time the Higgs boson, a key for the explanation of the mass component can be detected as well as the currently smallest known building blocks of matter, leptons and quarks, are examined for a possible substructure down. Parallel to the ATLAS pursued CMS detector physics similar program, so that a result of an experiment on each other can be checked. In the ATLAS experiment about 7,000 researchers from over 200 institutions around the world take part.

The construction of LHC was completed in February 2008, the first particle collisions found 2009. The plan is the operation of ATLAS until at least 2035.

Speaker of the collaboration is currently (2013 ) Dave Charlton. Before, Fabiola Gianotti (until February 2013) and Peter Jenni (until 2009) Speaker of the collaboration.

2012, the ATLAS collaboration has been involved with the independently operating CMS collaboration in the discovery of a new boson, which is probably the sought Higgs boson. The exact properties to be further explored.

  • 2.1 magnet system
  • 2.2 Inner Detector
  • 2.3 calorimeter
  • 2.4 muon detectors

Physics at the ATLAS experiment

With the ATLAS detector, the standard model of particle physics is reviewed and searched for possible physics beyond the Standard Model.

Origin of particle

An important area of ​​research is the question of how it comes to the very different masses of elementary particles. The masses range from the tiny, not yet precisely known masses of the neutrinos to the mass of the top quark, which corresponds to that of a gold atom. This is the heaviest elementary particles at least 200 billion times as heavy as the lightest. This experiment investigates the Higgs mechanism in this regard. Then create different particle masses, because particles of different couple strongly to the Higgs field. Therefore, it is hoped, be able to detect Higgs bosons as excitation of the Higgs field. This is possible, by examining the decays of the particles. Is a particle has been detected, which corresponds in all measured parameters with the predicted Higgs. But also remains unclear with the Higgs mechanism, why the coupling constants are so different.

Unification of interactions

The unification of the four fundamental interactions in a quantum field theory, which also includes the gravitation, constitutes another research focus. Since this unification until well done on energy scales beyond the experimentally accessible energy in the foreseeable future, a direct observation is not possible. Supersymmetry is a prerequisite for unification, therefore the goal is to ATLAS specifically for supersymmetric particles. If it were possible to detect supersymmetric partners of the known elementary particles today, at least three of the four fundamental forces in a large unified theory could be combined. So far (as of 2014) were discovered no new particles, however, the previous exclusion limits could be improved.

B- physics

In addition, B- physics is operated in the ATLAS detector. Here, the decay of B mesons and their antiparticles is observed. If there are differences in the probabilities for certain decay channels between particles and antiparticles, this is a violation of the CP symmetry. Such CP violating processes are prerequisite is that it can give as observed in the universe, more matter than antimatter. These measurements complement and check often results from the LHCb experiment, for example, in the mixing of Bs mesons. But one also hopes hitherto unknown CP- violating processes through the discovery of new particles, for example, to find the Higgs boson and supersymmetric particles.

Substructure of particles

In the field of elementary particle physics is examined whether leptons and quarks have a substructure and are therefore composed of other particles. This could possibly be found an answer to the question of whether there actually are exactly three generations of elementary particles and whether there are other undiscovered particles. So far (as of 2014) was not found substructure and such models were partially excluded.

Further analysis

In addition to these main tasks of the ATLAS detector is also designed to cover other fields of research. These include processes of quantum chromodynamics and the search for particles with anomalous quantum numbers such as leptoquarks or Dileptonen.

Construction of the detector

ATLAS has the shape of a cylinder with a length of 46 m and a diameter of 25 m and has a weight of 7,000 tonnes. This makes it the largest particle detector ever built. The experiment consists of four main systems. The systems are, as in particle detectors for Colliding -Beam Experiments usual, arranged in an onion-skin structure with each layer measuring only selected particles and only certain properties of these particles.

Magnet system

The magnet system generates a magnetic field which deflects charged particles. It consists of a central solenoid magnetic field of 2 T, the end cap and the barrel toroids toroids. Toroids are magnets in the shape of a torus, which produce a very homogeneous magnetic field inside. The curvature of the trajectory of charged particles whose pulse can be determined.

Inner detector

The Inner Detector consists of three sub-detectors. The innermost part of the ATLAS pixel detector with three layers of silicon sensors. The sensors start at a distance of 50.5 mm around the region of interaction of radiation and allow a high resolution of the individual interaction points. To the pixel detector around a silicon strip detector follows, which provides more tracking points to determine the flight path. The transition radiation tracker (English Transition Radiation Tracker, TRT) is the outermost part of the inner detector and registered about 30 points per track continuous ionizing particle. Through the detection of transition radiation can also be made between electrons and hadrons.

Calorimeter

The calorimeter consists of an electromagnetic calorimeter and a hadronic calorimeter. The entire electromagnetic and hadronic parts of the calorimeter using liquid argon as the active detector material and were therefore installed in a total of three cryostat. The outer part of the hadronic calorimeter based on scintillator technology. The electromagnetic calorimeter determines momentum and energy of electromagnetically interacting particles. The interaction cross section is inversely proportional to the mass of the charged particle, which is why priority electron -photon showers and barely heavier muons are detected. The subsequent outward hadronic calorimeter determines the type and energy of hadrons.

Muon detectors

Two different muon systems are used. The first system (precision chambers ) with a high spatial resolution is primarily used for the determination of trace progress and momentum of the muons, the second is primarily for triggering, that is for quick marking of physically interesting events used with muons. The muons can be measured separately from other particles because they are not involved in the strong interaction and can traverse freely the calorimeter because of their large mass.

Compact Muon Solenoid ALICE: A Large Ion Collider Experiment MoEDAL experiment B-Meson Semiconductor detector Calorimeter (particle physics)
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