On the possibility of positive-ion detection in gaseous TPCs and its potential use for neutrinoless double beta decay searches in ¹³⁶Xe

Abstract

The neutralization of slow positive ions on solid surfaces can lead to the emission of secondary electrons in Auger-type processes. We discuss the possibility of harnessing such mechanisms to the detection of positive ions in gaseous TPCs. Applied to high pressure xenon, the proposed idea may enable reconstructing with high accuracy the topology of candidate neutrinoless double beta decay events of 136 Xe without sacrificing the energy resolution of pure Xe gas. Candidate secondary electron emitters are discussed, as well as the expected efficiencies, challenges and potential pitfalls.

Helium–Xenon mixtures to improve the topological signature in high pressure gas xenon TPCs

“…After one meter of drift, a point-like ionization deposit becomes a cloud distributed as a gaussian of 10 mm sigma in the direction perpendicular to the electric field (transverse) and 4 mm in the parallel direction (longitudinal). This situation is far from ideal and can be largely improved by adding molecular electron coolants to the gas [5,6] or by positive-ion detection [7]. As a reference, the thermal diffusion limit which can be found in [8] gives a diffusion factor of ∼1.5 mm/ √ m for a field of 250 V/cm, which is very close to the ∼2.5 mm/ √ m value obtained for instance in Xe/CO 2 mixtures [6].…”

Gaseous and dual-phase time projection chambers for imaging rare processes

“…Since the probability depends on the difference between the ionization potential of the ion and twice the work function of the surface material, a suitable material selection, handling, and treatment will be needed. The author in [58] aims at γ i = 2 × 10 −3 , a value compatible with the values obtained in vacuum by Hagstrum in [437] after including electron extraction efficiencies in gas obtained from [438]. Positive ions could hence make available a T o -signal for energy deposits of the order 10-20 keV, as well as precise topological information for the case of extended tracks capable of creating a sufficiently high ionization density.…”

“…For nuclear decays, the ultimate milestone would be to be able to identify the daughter nucleus, some-thing that is actively pursued in liquid as well as in gas for the case of 136 Xe [55,56]. Lastly, a bold proposal for the detection of positive ions by resorting to Auger emission upon neutralization at the cathode has been recently made in [58], despite it lacks experimental verification yet. It could be used, in its simplest version, for T 0 -determination in the absence of primary scintillation.…”

“…A new and radically different approach towards an ion-TPC consists on using the positive ions produced during the ionization [58]. Indeed, positive ions can ionize the gas or even the cathode with high efficiency, if a sufficiently high kinetic energy (O(10's of eV)) can be gained in the electric field.…”

“…Besides imaging the primary ionization with high accuracy they can, in some configurations, retrieve essential information from the gas scintillation, too. As we will see throughout the text, and in particular in section 6, there are numerous hints that future TPCs will be able to do more than 'just' that (e.g., [45,[55][56][57][58][59][60]. [61]; b) LUX, the dual-phase (optically read) xenon TPC for dark matter searches at the Sanford Underground Research Facility (SURF) [62]; c) NEW, the high pressure xenon TPC (optically read) developed for phase-I of the ββ0ν experiment NEXT, at Laboratorio Subterráneo de Canfranc (LSC) [12,63]; d) phase-I of the (Micromegas-based) Active Target TPC (AT-TPC), at the Facility for Rare Isotope Beams (FRIB) in Michigan [34]; e) 3 × 1 × 1 m 3 dual-phase argon prototype based on LEMs/thick GEMs for the far detector of the neutrino oscillation experiment DUNE [64]; f) The DarkSide-50 dual-phase argon detector for dark matter searches at Laboratori Nazionali del Gran Sasso (LNGS) [43].…”