Compact Muon Solenoid

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Large Hadron Collider (LHC) Arrangement of the various accelerators and detectors of the LHC
Arrangement of the various accelerators and detectors of the LHC
Detectors
 Partly built up:
Pre-accelerator

Coordinates: 46 ° 18 ′ 34 "  N , 6 ° 4 ′ 37"  E ; CH1903:  495106  /  129583 The Compact Muon Solenoid experiment ( CMS ) is a particle detector at the Large Hadron Collider (LHC) at CERN in Switzerland . The location of the experiment is an underground hall in the accelerator ring near Cessy in France .

The main goals of the experiment are:

  • the discovery of the Higgs boson (achieved) and the research into the physics of the Higgs boson
  • the search for evidence of supersymmetry or, in general, of still unknown particles
  • the study of the collision of heavy ions .

The group comprises more than 5800 people from around 200 scientific institutes worldwide.

The name of the detector describes its design:

As with most other detectors, the magnet enables the charge- to- mass ratio to be determined by measuring the curvature of the particle track in the magnetic field , similar to a mass spectrometer .

The spokesman for the experiment is currently (2018) Joel Butler , previously Tiziano Camporesi , Joe Incandela , Michel Della Negra , Tejinder Virdee and Guido Tonelli . In 2012, the CMS collaboration was involved in the discovery of a new boson , the measurement results of which are compatible with the Higgs boson , together with the independently working second large collaboration ATLAS . The exact properties still need to be researched.

construction

Cavern for installing the detector
End caps of the iron yoke of the detector magnet

The CMS detector is built up in several layers, which allow a precise measurement of all the particles produced during proton collisions.

From the inside out, the detector consists of the following components:

  • A silicon - pixel detector d. H. a semiconductor detector that uses very small silicon structures to detect charged particles. The spatial resolution is in the range of 0.01 mm.
  • A silicon strip detector, which, like the pixel detector, uses silicon as the detection material, but with a worse - but still very good - spatial resolution of significantly better than 0.1 mm.
  • An electromagnetic calorimeter with lead tungstate - crystals for the detection of photons and electrons (or positrons)
  • A hadronic calorimeter with brass plates, which alternate with layers of scintillators in order to be able to measure hadrons such as protons, pions or kaons.
  • In the return yoke of the magnet coil there are muon chambers that are specially designed for the detection of muons .

assembly

The detector was first assembled and tested largely on the surface and then lowered into the cavern in individual parts. The lowering of the large parts was completed on January 22, 2008.

The substructures of the silicon track detector were assembled and tested on the CERN premises. The transport to Cessy was carried out in December 2007.

Physics with the CMS detector

The standard model of particle physics is checked with the CMS detector and possible physics beyond the standard model is sought.

Origin of the particle masses

Since the electroweak interaction is a gauge theory , its interaction particles should be massless. In fact, a mass is observed for W bosons and Z bosons . One possible explanation for this is the Higgs mechanism . The particle masses are created by coupling to a Higgs field. The same mechanism can give mass to all other particles. One of the predictions of this description is the existence of at least one new particle, the Higgs boson . The collaboration of the CMS detector, together with the independent ATLAS collaboration, discovered a new particle that agrees with the predictions for the Higgs boson in all measured properties. Further measurements will determine the properties more precisely and also examine whether it is the only such particle.

Supersymmetry

It is possible that there is a supersymmetric partner for every known particle , with different spin and different mass, but otherwise similar properties. Supersymmetry would clarify some open questions in theoretical physics. So far (2015) no supersymmetric partner particles have been found, but the previous exclusion limits have been greatly improved.

CP violation

CP violation is a difference between matter and antimatter. The known differences are too small to explain why the universe consists only of matter. New sources of CP violation are searched for in the investigation of B mesons , among other things , but also in the decay of the Higgs boson and other particles.

More precise measurement of the standard model

The standard model contains several free parameters, the values ​​of which can only be determined experimentally. These are in particular the particle masses. In addition, some processes in hadrons such as the proton are difficult to describe in purely theoretical terms. Since the LHC causes protons to collide, understanding their internal structure is important. Measurements with CMS help to specify the free parameters and to describe the proton structure more precisely.

Further analysis

In addition to the above-mentioned focal points, there is a general search for new things, for example hypothetical microscopic black holes , gravitons , heavier excited states of known particles, or as yet unknown heavy particles in general.

Web links

Commons : Compact Muon Solenoid  - Album with pictures, videos and audio files

Individual evidence

  1. ↑ New results indicate that particle discovered at CERN is a Higgs boson | Media and Press Relations. In: CERN. CERN, March 14, 2013, accessed September 13, 2018 .
  2. ^ Aneta Iordanova, Heavy-Ion Physics with CMS , Rencontres de Moriond QCD and High Energy Interactions 2008
  3. ↑ List of the persons and institutes involved , accessed on August 2, 2015
  4. ↑ The Compact Muon Solenoid Experiment http://www.stfc.ac.uk/ , Science & Technology. Retrieved December 20, 2015.
  5. ↑ CMS management , accessed February 13, 2018
  6. ↑ Report in the CMS Times
  7. ↑ CMS Supersymmetry Physics Results. Accessed December 22, 2015 .
  8. ↑ constraints on the proton parton distribution functions from the Large Hadron Collider , MR Sutton, ATLAS and CMS collaborations, accessed on 22 December 2015