Abstract
In the search for the neutrinoless double beta decay of 136Xe, a high pressure xenon time projection chamber (HPXe-TPC) has two advantages over liquid xenon TPCs: a better energy resolution and the access to topological features, which may provide extra discrimination from background events. The PandaX-III experiment has recently proposed a 200 kg HPXe-TPC based on Micromegas readout planes, to be located at the Jinping Underground Laboratory in China. Its detection concept is based on two results obtained within the T-REX project: Micromegas readouts can be built with extremely low levels of radioactivity; and the operation in xenon-trimethylamine at 10 bar in realistic experimental conditions has proven an energy resolution of 3% FWHM at the region of interest. In this work, two discrimination methods are applied to simulated signal and background data in a generic 200 kg HPXe-TPC, based on two well-known algorithms of graph theory: the identification of connections and the search for the longest path. Rejection factors greater than 100 are obtained for small pixel sizes and a signal efficiency of 40%. Moreover, a new observable (the blob charge density) rejects better surface contaminations, which makes the use of a trigger signal (T0) not imperative in this experiment.
Highlights
Experiments based on liquid xenon are leading the search of neutrinoless double beta decay of 136Xe due to the fast development of this detection technique in the last decade [1]
Experiments based on high pressure xenon time projection chambers (HPXeTPCs) [2, 3] have been proposed due to their better intrinsic energy resolution (∼1% FWHM) and the access to topological features, which may provide extra discrimination from background events, keeping good signal efficiency
The use of Micromegas charge readout planes [4] in a HPXe-TPC has been studied by T-REX project2, leading to the following results: Micromegas readouts show extremely low levels of radioactivity [5]; they have been operated in xenon-trimethylamine (Xe-TMA) at 10 bar in realistic experimental conditions (30 cm diameter readout, 1200 channels, 38 cm drift), proving an energy resolution of 3% FWHM at the Range of Interest (RoI) [6]; and the combination of high granularity readout planes and low diffusion can reduce the background level by two-three orders of magnitude keeping a signal efficiency of 40% [7]
Summary
Experiments based on liquid xenon are leading the search of neutrinoless double beta decay of 136Xe due to the fast development of this detection technique in the last decade [1]. Experiments based on high pressure xenon time projection chambers (HPXeTPCs) [2, 3] have been proposed due to their better intrinsic energy resolution (∼1% FWHM) and the access to topological features, which may provide extra discrimination from background events, keeping good signal efficiency In this context, the use of Micromegas charge readout planes [4] in a HPXe-TPC has been studied by T-REX project, leading to the following results: Micromegas readouts show extremely low levels of radioactivity (below 0.1 μBq/cm for both 214Bi and 208Tl) [5]; they have been operated in xenon-trimethylamine (Xe-TMA) at 10 bar in realistic experimental conditions (30 cm diameter readout, 1200 channels, 38 cm drift), proving an energy resolution of 3% FWHM at the Range of Interest (RoI) [6]; and the combination of high granularity readout planes and low diffusion (as measured in Xe-TMA) can reduce the background level by two-three orders of magnitude keeping a signal efficiency of 40% [7]
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