Why a homogeneous dual readout calorimeter won't work

Abstract

If the response to a hadronic shower in a semi-infinite uniform calorimeter structure is S relative to the electronic response, then S/E = [fem + (1 – fem)(h/e)], where E is the incident hadron energy, fem is the electronic shower fraction, and h/e is the hadron/electron response ratio. In conventional calorimeters the resolution is dominated by the stochastic variable fem, whose broad, skewed pdf has an energy-dependent mean. The slow increase of the mean with E is responsible for response nonlinearity and the skewness results in a non-Gaussian response. If the cascade is observed in two channels with different values of h/e (typically scintillator(S) and Cherenkov (C)), fem can be eliminated. An energy estimator, linear in C and S, is obtained which is proportional to the incident hadron's energy. The resolution depends upon the contrast in h/e between the two channels. The Cherenkov h/e will be 0.20–0.25. In sampling calorimeters, h/e can be increased to about 0.7 by arranging for preferential absorption of the electromagnetic (EM) shower energy in the absorber (decreasing e) and using a hydrogenous detector (organic scintillator) to enhance h through the contribution of recoil protons in n–p scattering. Neither mechanism is available in a homogeneous crystal or glass scintillator, where h/e is expected to be in the vicinity of 0.4 because of invisible hadronic energy loss and other effects. The h/e contrast is very likely too small to provide the needed energy resolution. We support this conclusion with simple Monte Carlo simulations.