  The ARAPUCA is a novel technology for the detection of liquid argon
scintillation light, which has been proposed for the far detector of the Deep
Underground Neutrino Experiment. The X-ARAPUCA is an improvement to the
original ARAPUCA design, retaining the original ARAPUCA concept of photon
trapping inside a highly reflective box while using a wavelength shifting slab
inside the box to increase the probability of collecting trapped photons onto a
silicon photomultiplier array. The X-ARAPUCA concept is presented and its
performances are compared to those of a standard ARAPUCA by means of analytical
calculations and Monte Carlo simulations.
