DUGi

Characterization of a medium size Xe/TMA TPC instrumented with microbulk Micromegas, using low-energy γ-rays

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@372195

NEXT-MM is a general-purpose high pressure (10 bar, ~ 25 l active volume) Xenon-based TPC, read out in charge mode with an 0.8 cm × 0.8 cm-segmented 700 cm2 plane (1152 ch) of the latest microbulk-Micromegas technology. It has been recently commissioned at University of Zaragoza as part of the R&D of the NEXT 0νββ experiment, although the experiment’s first stage is currently being built based on a SiPM/PMT-readout concept relying on electroluminescence. Around 2 million events were collected during the last months, stemming from the low energy γ-rays emitted by a 241Am source when interacting with the Xenon gas (Eγ = 26, 30, 59.5 keV). The localized nature of such events around atmospheric pressure, the long drift times, as well as the possibility to determine their production time from the associated α particle in coincidence, allow the extraction of primordial properties of the TPC filling gas, namely the drift velocity, diffusion and attachment coefficients. In this work we focus on the little explored combination of Xe and trimethylamine (TMA) for which, in particular, such properties are largely unknown. This gas mixture offers potential advantages over pure Xenon when aimed at Rare Event Searches, mainly due to its Penning characteristics, wave-length shifting properties and reduced diffusion, and it is being actively investigated by our collaboration. The chamber is currently operated at 2.7 bar, as an intermediate step towards the envisaged 10 bar. We report here its performance as well as a first implementation of the calibration procedures that have allowed the extension of the previously reported energy resolution to the whole readout plane (10.6% FWHM@30 keV)

NEXT is supported by the following agencies and institutions: the Ministerio de Economía y Competitividad (MINECO) of Spain under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), FPA2009-13697-C04-04 and FIS2012-37947-C04; the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02- 05CH11231; and the Portuguese FCT and FEDER through the program COMPETE, projects PTDC/FIS/103860/2008 and PTDC/FIS/112272/2009. J. Renner (LBNL) acknowledges the support of a US DOE NNSA Stewardship Science Graduate Fellowship under contract no. DE-FC52- 08NA28752. The development of NEXT-MM in particular has important contributions from the European Research Council T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; and also MINECO under grants FPA2008-03456, FPA2011-24058 and CPAN under grant CSD2007- 00042

Institute of Physics (IOP)