Impact of the positive ion current on large size neutrino detectors and delayed photon emission

Given their small mobility coefficient in liquid argon with respect to the electrons, the ions spend a considerably longer time in a sensitive detector volume instrumented with an electric field. We studied the effects of the positive ion current in a liquid argon time projection chamber, in the context of massive argon experiments for neutrino physics. The constant recombination between free ions and electrons produces a quenching of the charge signal and a constant emission of photons, uncorrelated in time and space to the physical interactions. The predictions evidence some potential concerns for multi-ton argon detectors, particularly when operated on surface.