Speaker
Description
Modern neutrino experiments require precision reconstruction of events. A
crucial component of this reconstruction is the stopping power for charged
particles, calculated using the Bethe equation. The main free parameter of the
Bethe equation is the mean excitation energy (the "I-value"), which in most
cases cannot be calculated, but must be measured for each substance. In many
cases, the values are derived from very old experiments with large quoted
uncertainties, or worse, small quoted uncertainties and inadequate treatment of
systematics. Even if the tabulated values were reliable to the necessary
degree, the I-value is affected by the phase of the substance and by chemical
bonding, and only rough heuristics have been developed to convert measurements
of single elements into I-values for compounds or from one phase to another.
Modern neutrino experiments which need to measure an absolute energy scale,
while lacking calibration sources, suffer the most from uncertainties in the
I-value. DUNE is a primary example. We are performing measurements with the
400MeV Fermilab LINAC beam at the Irradiation Test Facility. We describe our
efforts to measure the I-value of liquid argon, as well as those for several
other materials used in past, present and potential future neutrino
experiments, including water, NOvA scintillator, MINOS steel, zirconium, and
molybdenum. These measurements use a set of degraders to scan the beam energy
around the Bragg peak for each substance to determine the proton range.
Experimental results are compared to results from Geant4 and FLUKA to determine
the I-value.