Wing Sheung Chan

34 The Large Hadron Collider and the ATLAS detector Figure 2.3.: A computer-generated cutaway view of the ATLAS detector [68] . the collision occurred, or “secondary vertices”, the position where short-live d † particles decayed into other particles before reaching the detector. Tracks are bent by the magnetic field generated by the superconducting solenoid surrounding the inner detector. This allows the determination of the charges and momenta of particles. Leaving the inner detector, particles will then travel into the calorimeters where they interact with the materials and deposit energy into them. The deposited energy is then measured. There are multiple calorimeters in the ATLAS detector. They interact differently with different types of particles, producing differential responses that help to identify the particles. By associating tracks in the inner detector with energy deposits in the calorimeters, both the direction and the energy of a particle can be precisely determined. While most particles are stopped by the calorimeters where they deposit all of their energies, muons usually pass through the calorimeters with only very limited interactions. Muons leaving the calorimeters are met by the muon spectrometer. Somewhat similar to the inner detector, the muon spectrometer registers hits when muons travel through it and reconstruct tracks from it. The muon spectrometer is provided with a magnetic field generated by a superconducting toroidal magnet. Similar to the case in the inner detector, the magnetic field in the muon spectrometer bends muon trajectories so that their charges and momenta can be measured. Figure 2.4 provides a neat summary of how different particles can be detected by the ATLAS detector. † But long-lived enough to have travelled a measurable distance before they decay