While staying in Switzerland I had an opportunity to visit, I would say, the most impressive experiment in the world- the LHC (Large Hadron Collider) at CERN (the European Organization for Nuclear Research). I was lucky enough to come during the time when the experiment is stopped for an upgrade and therefore, some of it’s parts are open. As I was guided by Dr Jad Marrouche, who is from Imperial and works at CERN, he showed us the experiment he works on- The Compact Muon Solenoid experiment (CMS). CMS is, however, only one of four biggest experiments that are at the LHC (there are also three smaller ones) others are ALICE (A Large Ion Collider Experiment), LHCb (Large Hadron Collider beauty), and ATLAS (A Toroidal LHC Apparatus).
Basically, LHC is a 27km ring in which beams of protons that are traveling nearly at the speed of light are smashed together. At the points were collisions happen the four big experiments are placed. The experiments use data from collisions not only to investigate particles produced (done by ATLAS and CMS), but also to understand the beginnings of the Universe (ALICE) and explain differences between matter and antimatter (LHCb).
Bellow I made a diagram of how CMS detects different particles.
Silicon tracker– made of silicon strip detectors and pixels which together give information about the track of particles. Uncharged particles such as photons will move in a straight path whereas charged ones (protons, electrons) will have curved tracks due to the CMS magnetic field.
Electromagnetic Calorimeter (EC)– place where electrons and photons are detected. EC is made of 76,000 PbWO4 crystals that produce scintillation light when a particle travels through them (this allows to measure the energy of a particle). The crystals need to be calibrated every 15min to get the most accurate measurement.
Hadronic Calorimeter (HC)- detects particles made of quarks and gluons (e.g. protons and neutrons). HC uses wavelength-shifting fibers to measure the amount of light produced as the particle crosses the material. Interestingly, for the making of parts of HC more than one million of WWII brass shell casements from Russian Navy have been used.
Magnet (Superconducting solenoid (SC))- allows to bend the track of charged particles. Generates a magnetic field of 4 Tesla, which is around 100,000 times that of the Earth’s magnetic field! Magnet has to be cooled down to -269Co in order to keep it in the superconducting state (the cooling down is what uses up most of the energy needed for CMS to run).
Muon chambers (MC)- obviously, detects muons. Muons are 200 times heavier than electrons or positrons and don’t interact with any of the layers beforehand. MC is a one of the most important layer of CMS as the theory predicts that Higgs Boson should decay into four muons.