13.8 billions years ago, equal quantities of matter and antimatter were created during the Big Bang. After only 1 second, while the Universe was cooling and expending, antimatter had almost disappeared, allowing matter to form everything around us such as stars, planets and life. The LHCb experiment, located 100m underground at the French-Swiss border, investigates the mystery of the vanishing of antimatter by exploring the physics of particles made of b (beauty) quarks and c (charm) quarks. LHCb is one of the four biggest experiments of the Large Hadron Collider (LHC) at CERN. The LHCb experiment is an international collaboration of around 1200 members from 73 institutes in 16 countries across the globe. The geometry of the LHCb detector is based on the fact that hadrons made of b and c quarks are predominantly produced in the same forward or backward cone. The detector is a series of sub-detectors each having a specific task:
- The Vertex Locator (called VELO) is placed at the proton-proton interaction point of the LHC. It is a silicon detector allowing a precise reconstruction of the hadrons’ decay vertices.
- RICH1 and RICH2 are detectors based on the Cherenkov effect. It allows particle identification.
- The TT, T1, T2 and T3 trackers provide a reconstruction of the particle tracks.
- The magnet placed between the TT and T1, T2, T3 stations curves the trajectory of the charged particles to obtain a precise measurement of their momentum.
- The electromagnetic calorimeters (ECAL) and hadronic calorimeters (HCAL) are necessary to measure the energy of the electrons, photons and hadrons.
- The five muon stations M1-M5 identify the muon passage, being the only particles capable of traversing the ECAL and HCAL chambers.
The research program of the LHCb collaboration is very diversified. Here are the main points:
- Measurements of the CP violation parameters in the decays of particles made of b quarks.
- Search for CP violation in the decays of particles made of c quarks.
- Tests of lepton universality through various decays.
- Study of hadrons made of more than 3 quarks, called tetraquarks (4 quarks) and pentaquarks (5 quarks).
- Search for rare decays (meaning that the Standard Model predictions account for very small branching ratios).
- Search for new particles through direct and indirect measurements.
- Study of heavy ion collisions inside the LHCb detector.