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

Abstract

Within the framework of xenon-based double beta decay experiments, we propose the possibility to improve the background rejection of an electroluminescent Time Projection Chamber (EL TPC) by reducing the diffusion of the drifting electrons while keeping nearly intact the energy resolution of a pure xenon EL TPC. Based on state-of-the-art microscopic simulations, a substantial addition of helium, around 10 or 15 %, may reduce drastically the transverse diffusion down to 2.5 mm/ √ m from the 10.5 mm/ √ m of pure xenon. The longitudinal diffusion remains around 4 mm/ √ m. Light production studies have been performed as well. They show that the relative variation in energy resolution introduced by such a change does not exceed a few percent, which leaves the energy resolution practically unchanged. The technical caveats of using photomultipliers close to an helium atmosphere are also discussed in detail.

Demonstration of the event identification capabilities of the NEXT-White detector

“…Furthermore, different algorithms based, for instance, on Deep Neural Networks or Maximum-Likelihood Expectation Maximization have the potential to improve the topo-JHEP10(2019)052 logical discrimination [17,18]. The discrimination efficiency is expected to be increased also by having a gas with reduced electron transverse diffusion, such as Xe with subpercent concentration of a molecular additive [19,20] or Xe-He mixtures [21,22].…”

Low-diffusion Xe-He gas mixtures for rare-event detection: electroluminescence yield

“…In this work, only relative values were measured for the EL yield. In each run, absolute values for the reduced EL yield, Y/p, were obtained by normalizing the pulse amplitude measured for pure xenon at an E/p of ∼2.0 kV/cm/bar to the corresponding absolute value obtained in [33]. The same normalization constant has been used, then, to normalize the remaining centroid values obtained for the different E/p for pure xenon and for the two Xe-He mixtures studied in that run.…”

“…For the mixtures of Xe-15% He and Xe-20% He, a single linear function was fitted to the whole set of data points, displaying the average linear trend for each He-concentration. For comparison, the simulation results obtained with the simulation tool of [33] are also depicted in figure 8 (dashed lines). Table 1 lists the EL amplification parameter and the scintillation threshold obtained from the linear fits to the experimental data for each of the studied mixtures.…”

“…While the aforementioned aspects are yet to be studied in higher detail in real-size detectors, and may be certainly overcome, the addition of a noble gas such as He could offer an alternative solution, free from those limitations [32,33]. Simulation studies of electron drift parameters, as well as primary and secondary scintillation yields of Xe-He mixtures have been carried out recently [33]. The significantly lower mass of helium atoms, when compared to xenon, allows more efficient cooling of the electrons along the drift path.…”

“…Yet, the use of such mixture would reduce the amount of the source isotope in the detector. The final value of the helium concentration should be a compromise between an improvement of the background rejection factor and a reduction of the active mass that is needed to maximize sensitivity, as noted in [33].…”