The L3 experiment was one of the four large detectors on the

Large Electron–Positron Collider The Large Electron–Positron Collider (LEP) was one of the largest particle accelerators ever constructed. It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP collided electr ...

(LEP). The detector was designed to look for the physics of the

Standard Model The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...

and beyond. It started up in 1989 and stopped taking data in November 2000 to make room for construction of the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

(LHC). Now, the ALICE detector sits in the cavern that L3 used to occupy, reusing L3's characteristic red octagonal magnet.

Detector

The L3-detector was a multi-layered cylindrical set of different devices, each of them measuring physical quantities relevant to the reconstruction of the collision under study. Starting from the centre, close to the pipe where electrons and positrons circulate and collide, there were first the Silicon strip Microvertex Detector (SMD) and the Time Expansion Chamber (TEC). These two sub-detectors traced the paths of charged particles produced in the collision. One also gathered information about the momentum (a quantity related to mass and energy) of the particles by measuring their deflection in the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

present in the detector. The three main outer layers were the electro-magnetic

calorimeter A calorimeter is a device used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters ...

(also called BGO because it is made of bismuth germanium oxide), the hadronic calorimeter (HCAL) and the

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of ''ħ'', but with a much greater mass. It is classified as a ...

detector. Calorimeters are dense and stop most particles, measuring their energy. A set of scintillation counters was placed between the electro-magnetic and hadronic calorimeters: one of their functions was to help in recognising and rejecting signals coming from cosmic ray muons, very highly energetic particles which come from the space and can disturb the measurement. The outermost layer contained the magnet that generated, inside the detector, a magnetic field about 10,000 times the average field on the surface of the Earth. This field deflected the charged particles which crossed it and the curvature of this deflection was a way of reconstructing the energy of the particles. Another important part of the detector were the two luminosity monitors, placed along the beam on both sides of the interaction point. They measured the "luminosity" of the beam, which is a way of quantifying the rate of interactions produced. L3 Website
CERN.

References

External links

*
Scientific publications of the L3 Collaboration
on

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{{DEFAULTSORT:L3 Experiment CERN experiments Particle experiments