We model the response of a state of the art micro-hole single-stage charge amplication device (`microbulk Micromegas) in a gaseous atmosphere consisting of Xenon/trimethylamine at various concentrations and pressures. The amplifying structure, made w
ith photo-lithographic techniques similar to those followed in the fabrication of gas electron multipliers (GEMs), consisted of a 100 um-side equilateral-triangle pattern with 50 um-diameter holes placed at its vertexes. Once the primary electrons are guided into the holes by virtue of an optimized field configuration, avalanches develop along the 50 um-height channels etched out of the original doubly copper-clad polyimide foil. In order to properly account for the strong field gradients at the holes entrance as well as for the fluctuations of the avalanche process (that ultimately determine the achievable energy resolution), we abandoned the hydrodynamic framework, resorting to a purely microscopic description of the electron trajectories as obtained from elementary cross-sections. We show that achieving a satisfactory description needs additional assumptions about atom-molecule (Penning) transfer reactions and charge recombination to be made.
Phase I of the NEXT-100 $0 ubetabeta$ experiment (NEW) is scheduled for data taking in 2015 at Laboratorio Subterraneo de Canfranc in the Spanish Pyrenees. Thanks to the light proportional technique, NEW anticipates an outstanding energy resolution n
earing the Fano factor in Xenon (0.5-1%FWHM@$Q_{betabeta,^{136}Xe}$), with a TPC-design that allows tracking and identification of the double end-blob feature of the $0 ubetabeta$ decay. When properly mastered, the combination of these two assets can suppress the irreducible $2 ubetabeta$ and (single-blob) $gamma$ backgrounds from natural radioactivity to minute levels, of the order of $5times{10^{-4}}$ ckky. Given our knowledge of the available phase-space as obtained from neutrino oscillation experiments, this feat will expectedly allow for a sensitivity to the effective electron neutrino mass of $m_{betabeta}simeq 30$ meV for exposures at the 20 ton $times$ year scale. Hence, ultimately, a full survey of the inverse hierarchy of the neutrino mass ordering appears to be within reach for a ton-scale experiment based on this technology. NEW, with 10 kg of Xenon 90%-enriched in $^{136}$Xe, sets an unprecedented scale for gaseous Xenon TPCs and will be an important milestone for its anticipated upgrades (100 kg and 1 ton). I briefly summarize the status of the NEXT experiment, from the main results obtained with $sim 1$ kg prototypes that substantiate the concept, to the ongoing works for deploying its first phase.
Systematic measurements on the rate capability of thin MWPCs operated in Xenon, Argon and Neon mixtures using CO2 as UV-quencher are presented. A good agreement between data and existing models has been found, allowing us to present the rate capabili
ty of MWPCs in a comprehensive way and ultimately connect it with the mobilities of the drifting ions.
