Electron-ion recombination is experimentally studied in Xe+trimethylamine (Xe+TMA) mixtures, motivated by its potential use for directional dark matter searches. A Time Projection Chamber (TPC) of 2.4 l volume with a novel configuration formed by two symmetric drift regions is used to measure the charge collected from α-particles and γ-rays emitted in coincidence by an 241 Am source, by means of two microbulk-Micromegas readouts. Xe+TMA gas mixtures are used with TMA concentrations lower than 2%. The pressure was varied from 3 to 8 bar and the reduced drift field within 10-400 V/cm/bar. The charge collected from α-particles and γ-rays exhibit recombination as the drift field decreases, being stronger for α-particles. A significant part of the observed effect can be plausibly explained by columnar recombination, due to the dependency observed with the track angle (relative to the drift field direction). The results presented support a suggestion that has been recently put forward on how to obtain a directional signal for nuclear recoils induced by Dark Matter interactions with xenon. If finally demonstrated for nuclear recoils, this technique can be easily scaled to higher mass detectors like high pressure Xe TPCs.
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