Energy scaling of low-energy neutron yield, the e/π ratio, and hadronic response in a calorimeter

In each early collision in a high-energy hadronic cascade about 1/3 of the energy goes into π0's and is thereafter lost to hadronic interaction. As a result, the level of low-energy hadronic activity in an absorber (as measured by the total yield of ∼1 MeV neutrons, the total number of nuclear collisions above some cutoff energy, the response of a calorimeter when electromagnetic components are excluded, etc.) rises more slowly than linearly with energy. A naive induction argument yields a power law dependence with an exponent m near 0.85. Simulations with a variety of codes corroborate this result for E > 10 GeV. To the extent that this functional form is valid, the ratio of a calorimeter's response to an incident electron to that for an incident hadron is Re/Rh (= e/π) = 1/1 - (1 - εh/εe)(E/E0)m-1, where εe and εh are the calorimeter efficiencies for detecting low- energy electronic and hadronic energy deposition, respectively, and E0 is a scale factor near 1 GeV. This one-parameter function (if we neglect the slight m dependence) provides a good fit to available test-beam data, and has the correct asymptotic behavior. 15 refs., 14 figs