Abstract
Abstract
Current and future experiments need to know the stopping
power of liquid argon. It is used directly in calibration, where
commonly the minimum-ionizing portion of muon tracks is used as a
standard candle. Similarly, muon range is used as a measure of muon
energy. More broadly, the stopping power figures into the simulation
of all charged particles, and so uncertainty propagates widely
throughout data analysis of all sorts. The main parameter that
controls stopping power is the mean excitation energy, or
I-value. Direct experimental information for argon's I-value come
primarily from measurements of gaseous argon, with a very limited
amount of information from solid argon, and none from liquid argon.
A powerful source of indirect information is also available from
oscillator strength distribution calculations. We perform a new
calculation and find that from oscillator strength information
alone, the I-value of gaseous argon is (187 ± 5) eV. In
combination with the direct measurements and other calculations, we
recommend (187 ± 4) eV for gaseous argon. For liquid argon, we
evaluate the difference in central value and uncertainty incurred by
the difference of phase and recommend (197 ± 7) eV. All
uncertainties are given to 68% C.L.