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RTU Center of High Energy Physics and Accelerator Technologies

Compact Muon Solenoid Experiment

Compact Muon Solenoid Experiment

On December 2017 Consortium of two universities - RTU and UL joined the CMS experiment. Following areas of collaboration have been identified:

  • RTU technical integration – engineering – one staff member at CERN
  • RTU - Top physics – study of color flow in top quark pair decays – one scientist as author of CMS;
  • University of Latvia - Computing simulations - potentially TR2 service. One staff member – junior scientist;
  • University of Latvia - Contribution within Crystal Clear Collaboration.

The Compact Muon Solenoid (CMS) experiment was created to:

  1.  Search for the Higgs boson, the existence of which was foreseen already in 1964. The Higgs field explains why other elementary particles have mass. After 50 years of search, it was discovered in 2012. This discovery confirmed the correctness of our beliefs about the fundamental forces in nature.
  2. Look for the dark matter signal. The ordinary matter which we are made of comprise only 5% of the universe. The other 95% do not interact with our senses and measurement instruments. The presence of dark matter can only be inferred indirectly.
  3. Study the quark-gluon plasma. It is believed that the universe was in this state in the first microsecond after the Big Bang.
  4. Search for elementary particles yet unobserved, for example the supersymmetric partners of known particles.

A significant part of the research is on the top quark, the heaviest of all known particles. Its decay triggers many interesting physics processes.

The detector relies on a 4T magnetic field created by a superconducting solenoid. The ratio of the stored energy in the magnetic field to its mass is the largest among all detectors - it is a compact solenoid. The muons are created in many elementary particle processes and they are relatively simple to observe.

The CMS detector covers the point of interaction from all angles. Its different subdetectors are arranged in radial layers like in an onion.

The silicon tracker sits in the innermost layer. While traversing the tracker charged particles leave signals in silicon cells. The particle trajectory is reconstructed and the interaction point determined by connecting the activated cells
The next layer is the electromagnetic calorimeter which measures the electron and photon energy. It consists of scintillating crystals. The light energy generated by absorbed electrons and photons is measured by photodiodes.
Hadron energy is measured in the hadron calorimeter. The hadrons are absorbed in the brass layer, producing a hadron jet. The jet of hadrons induces a glow in a scintillating plastic material. The energy in this light is measured by photodiodes.

The tracker and the calorimeters are surrounded by a superconducting solenoid, which sets up a uniform magnetic field. The solenoid is cooled to a temperature of 4.5 K. The charged particles are deflected in the magnetic field. From the deflection the momentum of these particles can be measured.

Muons which are similar to electrons but much heavier elementary particles, pass through all of these layers and their trajectories are observed in the muon chambers. The muon chambers are filled with gas that is ionised when its atoms collide with the muons passing through the camera. The electric field in the chamber accelerates ions. When ions reach the electrodes, the signal for reconstructing the trajectory of the muons is generated.

The neutrino passes through all the layers of the detector without leaving any signal. We can infer about the existence of the neutrino only from the observation that they carry away a fraction of the energy and momentum.
The CMS experiment collects 5 petabytes of data a year. Their storage and processing are spread across the Worldwide Large Hadron Collider Computing Grid.

CMS is one of the four major experiments of the Large Hadron Collider. It is run by around 4,000 scientists, engineers and students from around 200 different institutes and universities in approximately 40 countries worldwide.

Research directions

RTU participates in the top quark physics group, undertaking a study of colour flow in top quark pair decays.