High resolution hadron calorimetry

Abstract

The components that contribute to the signal of a hadron calorimeter and the factors that affect its performance are discussed, concentrating on two aspects: energy resolution and signal linearity. Both are decisively dependent on the relative response to the electromagnetic and the nonelectromagnetic shower components, the e/ h signal ratio, which should be equal to 1.0 for optimal performance. The factors that determine the value of this ratio are examined. The calorimeter performance is crucially determined by its response to the abundantly present soft neutrons in the shower. The presence of a considerable fraction of hydrogen atoms in the active medium is essential for achieving the best possible results. Firstly, this allows one to tune e/ h to the desired value by choosing the appropriate sampling fraction. And secondly, the efficient neutron detection via recoil protons in the readout medium itself reduces considerably the effect of fluctuations in binding energy losses at the nuclear level, which dominate the intrinsic energy resolution. Signal equalization, or compensation ( e/ h = 1.0) does not seem to be a property unique to 238U, but can also be achieved with lead and probably even iron absorbers.