Principles of Particle Energy Determination

Abstract

Collisions between two particle beams (collider experiments) or by a beam interacting with a fixed-target (fixed-target experiments) or the interaction of cosmic rays with space matter or the Earth's atmosphere (astrophysics, gamma-ray astronomy, cosmic-ray studies) frequently produce a variety of particles through very complicated configurations of events covering a large solid angle.The geometry of the collisions imposes a defined structure to detectors. For instance, detectors operating in collider experiments have a barrel structure, with endcaps to cover the forward region. The occurrence of a large number of events to investigate and the variety of physics goals pursued impose the construction of a detector composed of many sub-detectors assigned to dedicated tasks. These sub-detectors have complementary capabilities which can be combined in a optimized way to measure the energy, mass, momentum, charge and direction of the particles produced. In particular, the measurement of particle energy is performed with calorimeters. A review of the properties of electromagnetic and hadronic shower propagation in matter and of calorimeters was provided by Leroy and Rancoita (2000).Calorimeters are instrumented blocks of matter in which the particle to be measured interacts and deposits all its energy in the form of a cascade of particles, whose energy decreases progressively down to the threshold of ionization and excitations that are detectable by the readout media. The deposited energy is detectable in the form of a signal which is proportional to the incoming energy. This proportionality is the base of calorimetry measurement.Calorimeters contribute also to the measurement of the position and angle of the incident particle. Their different response to electrons, muons, and hadrons can be exploited for particle identification. Neutrinos, which interact only weakly with matter, are detected through the absence of any energy deposit (missing energy).Electromagnetic calorimeters are used to measure the energy deposited by electromagnetic particles (electrons, photons), while the hadron (such as pions, protons) energy measurement is achieved with hadronic calorimeters. Furthermore, calorimeters are classified into two types: homogeneous calorimeters, where the incoming 611 Principles of Radiation Interaction in Matter and Detection Downloaded from www.worldscientific.com by UNIVERSITY OF QUEENSLAND on 10/12/15. For personal use only. Principles of Radiation Interaction in Matter and Detectionparticle energy is measured in a homogeneous block of sensitive absorbing material (lead-glass, sodium iodide (NaI) crystal, bismuth-germanium oxide (BGO) crystal, etc.), and the sampling calorimeters, where the incoming particle energy is measured in a number of sensitive layers interspersed with the layers of absorbing material, the latter speeding up the cascade process. Various active medium (scintillator, silicon * , liquid argon, gas, . . .) and absorbers (Fe, Cu, Pb, U, . . .) are used. Calorimeters † of all types were used a...