ATLAS (detector)
Large Hadron Collider (LHC)
 Arrangement of the various accelerators and detectors of the LHC
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Coordinates: 46 ° 14 '8.7 " N , 6 ° 3' 18.3" E ; CH1903: 493278 / 121422
ATLAS is a particle detector at the Large Hadron Collider (LHC), a particle accelerator at the European nuclear research center CERN . ATLAS was originally an acronym for AT oroidal L HC A pparatu S (in German about: " A toroidal LHC apparatus "), but is now only used as a proper name. Among other things, the Higgs boson , an important component for explaining mass , was detected with ATLAS . In addition, the smallest known building blocks of matter, leptons and quarks , are to be examined for a possible substructure. In parallel to ATLAS, the CMS detector also follows a similar physics program, so that the result of one experiment can be checked on the other. More than 7600 researchers from around 215 institutes worldwide are taking part in the ATLAS experiment.
Construction of the LHC was completed in February 2008, and the first particle collisions took place in 2009. ATLAS is planned to operate until at least 2035.
Karl Jakobs has been the spokesman for the collaboration since March 1, 2017 . Before that, David Charlton , Fabiola Gianotti (until February 2013) and Peter Jenni (until 2009) were the speakers for the collaboration.
In 2012, the ATLAS collaboration and the independently operating CMS collaboration discovered the Higgs boson . The exact properties are still being researched.
Physics at the ATLAS experiment
The standard model of particle physics is checked with the ATLAS detector and a search is made for possible physics beyond the standard model.
Origin of the particle masses
An important area of research is the question of how the masses of the elementary particles vary greatly. The masses range from the tiny, not exactly known masses of neutrinos to the mass of the top quark, which corresponds to that of a gold atom. This means that the heaviest elementary particle is at least 200 billion times as heavy as the lightest. In this context, the Higgs mechanism is examined . Then different particle masses arise because particles couple differently to the Higgs field. Therefore, Higgs bosons are measured as the excitation of the Higgs field. This can be done by studying the decay of the particles. However, it remains unclear even with the Higgs mechanism why the coupling constants are so different.
Unification of interactions and supersymmetry
The unification of the four fundamental interactions to a quantum field theory , which also includes gravity , is another research focus. Since this unification only takes place on energy scales far beyond the energies that can be experimentally achieved in the foreseeable future, direct observation is not possible. Supersymmetry is a prerequisite for standardization, which is why ATLAS searches specifically for supersymmetrical particles. If it were possible to prove supersymmetric partners of the elementary particles known today, at least three of the four basic forces could be combined in a large unified theory . So far (as of 2014) no new particles have been discovered, but the previous exclusion limits have been improved.
B physics
In addition, B-Physics is carried out at the ATLAS detector . 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 a prerequisite for the fact that there can be more matter than antimatter in the universe, as observed . These measurements supplement and often check the results of the LHCb experiment, for example in the case of the mixing of B s mesons or the rare decays B s → µµ and B 0 → µµ. However, it is hoped that previously unknown CP-violating processes will result from the discovery of new particles Find.
Substructure of particles
In the field of elementary particle physics , it is investigated whether leptons and quarks have a substructure and are therefore composed of other particles. This could possibly provide an answer to the question of whether there are actually exactly three generations of elementary particles and whether there are still other undiscovered particles. So far (as of 2014) no substructure has been found and such models could partially be excluded.
Further analysis
In addition to these main tasks, the ATLAS detector is also designed to cover other research fields. These include processes of quantum chromodynamics and the search for particles with abnormal quantum numbers such as leptoquarks or dileptons .
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 tons. This makes it the largest particle detector ever built. The experiment consists of four superordinate systems. As is customary with particle detectors for colliding beam experiments , the systems are 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 the magnetic field which deflects charged particles. It consists of a central solenoid magnetic field of 2 Tesla , the end cap toroid and the barrel toroid. Toroids are magnets in the shape of a torus , which generate a very homogeneous magnetic field inside. The curvature of the trajectory of charged particles can determine their momentum.
Inner detector
The inner detector consists of three sub-detectors. The innermost part is the ATLAS pixel detector with four layers of silicon sensors . The sensors start at a distance of 32 mm around the interaction area of the beams and allow a high resolution of the individual interaction points. A silicon strip detector is attached around the pixel detector, which provides additional tracking points for determining the flight path. The transition radiation track detector (engl. Transition Radiation Tracker , TRT) is the outermost part of the inner detector and registered about 30 points per lane continuous ionizing particles. The detection of transition radiation also enables a distinction to be made between electrons and hadrons .
Calorimeter system
The calorimeter system consists of an electromagnetic calorimeter and a hadronic calorimeter. The entire electromagnetic and parts of the hadronic calorimeter use liquid argon as the active detector material and were therefore installed in a total of three cryostats . The outer part of the hadronic calorimeter is based on scintillator technology. The electromagnetic calorimeter determines the momentum and energy of electromagnetically interacting particles. The interaction cross-section is inversely proportional to the mass of the charged particle, which is why it is primarily electron-photon showers that are detected. The hadronic calorimeter connected to the outside determines the energy of the hadrons.
Muon detectors
Two different muon detectors are used. The first system ( precision chambers ) with a high spatial resolution is primarily used to determine the trace and momentum of the muons, the second is primarily used for triggering, i.e. for the quick marking of physically interesting events with muons. The muons can be measured separately from other particles because they are not involved in the strong interaction and because of their large mass they can cross the calorimeter undisturbed.
literature
- ATLAS Detector and Physics Performance. Technical Design Report, ATLAS Collaboration, 25 May 1999, Volume 1. CERN-LHCC-99-014, Volume 2. CERN-LHCC-99-015
Web links
- ATLAS collaboration website
- ATLAS website of the German LHC researchers
- The physics investigated with ATLAS , written by the physics coordinator of the experiment
- Structure of the ATLAS detector
- The official website of the BMBF research focus "ATLAS experiment" (FSP 101)
Individual evidence
- ↑ List of participants , accessed on August 2, 2015
- ↑ Freiburg professor of physics becomes head of the ATLAS collaboration. (PDF) In: Press release of the Committee for Elementary Particle Physics. Retrieved April 12, 2017 .
- ↑ Issue 3 ( Memento of the original from May 6, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 162 kB) UK news from CERN
- ↑ Fabiola Gianotti took over the position of spokesperson in 2009 . In: CERN Courier , April 2009
- ↑ Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC . ATLAS collaboration. In: Phys. Lett. , B716, 2012, pp. 1-29, arxiv : 1207.7214 .
- ↑ ATLAS Supersymmetry (SUSY) searches. ATLAS collaboration, accessed on October 29, 2013 .
- ↑ ATLAS collaboration (ed.): Time-dependent angular analysis of the decay Bs → J / psi phi and extraction of Delta Gamma_s and the CP-violating weak phase phi_s by ATLAS . March 24, 2013, arxiv : 1208.0572 .
- ↑ ATLAS collaboration (ed.): Study of the rare decays of B s and B 0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector . September 29, 2016, arxiv : 1604.04263 .
- ^ Search for Production of Resonant States in the Photon-Jet Mass Distribution Using pp Collisions at √s = 7 TeV Collected by the ATLAS Detector . In: Phys. Rev. Lett. 108, 211802, 2012, arxiv : 1112.3580 .
- ↑ World's largest superconducting magnet switches on. CERN, November 20, 2006, accessed November 12, 2016 .
