Xenon TPC Research Articles

The NEW detector: construction, commissioning and first results

NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double-beta (ββ0ν) decay experiment at the Canfranc Underground Laboratory (LSC). It seeks to detect the ββ0ν decay of Xe-136 using a high pressure xenon gas TPC with electroluminescent (EL) amplification.The NEXT-White (NEW) detector, with an active xenon mass of about 10 kg at 15 bar, is the first NEXT prototype installed at LSC. It implements the NEXT detector concept tested in smaller prototypes using the same radiopure sensors and materials that will be used in the future NEXT-100, serving as a benchmark for technical solutions as well as for the signal selection and background rejection algorithms. NEW is currently under commissioning at the LSC.In this poster proceedings we describe the technical solutions adopted for NEW construction, the lessons learned from the commissioning phase, and the first results on energy calibration and energy resolution obtained with low-energy radioactive source data.

The potential of discrimination methods in a high pressure xenon TPC for the search of the neutrinoless double-beta decay of Xe-136

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.

Topological signature in the NEXT high pressure xenon TPC

The NEXT experiment aims to observe the neutrinoless double beta decay of 136Xe in a high-pressure xenon gas TPC using electroluminescence to amplify the signal from ionization. One of the main advantages of this technology is the possibility to use the topology of events with energies close to Qββ as an extra tool to reject background. In these proceedings we show with data from prototypes that an extra background rejection factor of 24.3 ± 1.4 (stat.)% can be achieved, while maintaining an efficiency of 66.7 ± 1.% for signal events. The performance expected in NEW, the next stage of the experiment, is to improve to 12.9% ± 0.6% background acceptance for 66.9% ± 0.6% signal efficiency.

Application and performance of an ML-EM algorithm in NEXT

The goal of the NEXT experiment is the observation of neutrinoless double beta decay in 136Xe using a gaseous xenon TPC with electroluminescent amplification and specialized photodetector arrays for calorimetry and tracking. The NEXT Collaboration is exploring a number of reconstruction algorithms to exploit the full potential of the detector. This paper describes one of them: the Maximum Likelihood Expectation Maximization (ML-EM) method, a generic iterative algorithm to find maximum-likelihood estimates of parameters that has been applied to solve many different types of complex inverse problems. In particular, we discuss a bi-dimensional version of the method in which the photosensor signals integrated over time are used to reconstruct a transverse projection of the event. First results show that, when applied to detector simulation data, the algorithm achieves nearly optimal energy resolution (better than 0.5% FWHM at the Q value of 136Xe) for events distributed over the full active volume of the TPC.

EXO-200 results and cosmogenic backgrounds

Status update and recent results from the double beta decay search experiment EXO-200 are presented. Detector is a liquid xenon TPC with charge and light readout located underground in low-background laboratory at 1600 m.w.e. depth. It contains 175 kg of xenon with 80.6% abundance of 136Xe, which acts as both the decaying nucleus and detection medium. Detector showed good performance and achieved remarkable results. The detector has demonstrated excellent energy resolution and background rejection capabilities and has set a lower limit on the 0νββ-decay half-life of 1.1 × 1025 years at 90% C.L. in early 2014. The EXO-200 collaboration has since published several papers on experimental backgrounds and searches for rare or exotic processes. After a two-year data interruption, EXO-200 is now back online with significant hardware improvements, including a radon reduction air system and a front end electronics upgrade for better energy resolution.

Commissioning of a dual-phase xenon TPC at Nikhef

A dual-phase xenon time-projection chamber was built at Nikhef in Amsterdam as a direct dark matter detection R&D facility. In this paper, the setup is presented and the first results from a calibration with a 22Na gamma-ray source are presented. The results show an average light yield of (5.6±0.3) photoelectrons/keV (calculated to 122keV and zero field) and an electron lifetime of (429±26)μs. The best energy resolution σE/E is (5.8±0.2)% at an energy of 511keV. This was achieved using a combination of the scintillation and the ionization signals. A photomultiplier tube gain calibration technique, based on the electroluminescence signals occurring from isolated electrons, is presented and its advantages and limitations are discussed.

The NEXT double beta decay experiment

NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double-beta (ββ0v) decay experiment at Laboratorio Subterraneo de Canfranc (LSC). It is an electroluminescent Time Projection Chamber filled with high pressure 136Xe gas with separated function capabilities for calorimetry and tracking. Energy resolution and background suppression are the two key features of any neutrinoless double beta decay experiment. NEXT has both good energy resolution (< 1% FWHM) and an extra handle for background identification provided by track reconstruction. We expect a background rate of 4 × 10-4 counts keV-1 kg-1 yr-1, and a sensitivity to the Majorana neutrino mass of between 80-160 meV (depending on NME) after a run of 3 effective years of the 100 kg scale NEXT-100 detector. The initial phase of NEXT-100, called NEW, is currently being commissioned at LSC. It will validate the NEXT background rate expectations and will make first measurements of the two neutrino ββ2v mode of 136Xe. Furthermore, the NEXT technique can be extrapolated to the tonne scale, thus allowing the full exploration of the inverted hierarchy of neutrino masses. These proceedings review NEXT R&D results, the status of detector commissioning at LSC and the NEXT physics case.

The NEXT experiment

NEXT (Neutrino Experiment with a Xenon TPC) is an experiment to search neutrinoless double beta decay processes (ββ0ν). The isotope chosen by NEXT is 136Xe. The NEXT technology is based in the use of time projection chambers operating at a typical pressure of 15 bar and using electroluminescence to amplify the signal (HPXe). The main advantages of the experimental technique are: a) excellent energy resolution; b) the ability to reconstruct the trajectory of the two electrons emitted in the decays, a unique feature of the HPXe which further contributes to the suppression of backgrounds; c) scalability to large masses; and d) the possibility to reduce the background to negligible levels thanks to the barium tagging technology (BaTa).The NEXT roadmap was designed in four stages: i) Demonstration of the HPXe technology with prototypes deploying a mass of natural xenon in the range of 1 kg; ii) Characterisation of the backgrounds to the ββ0ν signal and measurement of the ββ2ν signal with the NEW detector, deploying 10 kg of enriched xenon and operating at the LSC; iii) Search for ββ0ν decays with the NEXT-100 detector, which deploys 100 kg of enriched xenon; iv) Search for ββ0ν decays with the BEXT detector, which will deploy masses in the range of the ton and will introduce two additional handles, only possible in a HPXe: a) A magnetic field, capable of further enhancing the topological signal of NEXT; and b) barium-tagging (a technique pioneered by the EXO experiment which is also accessible to NEXT).The first stage of NEXT has been successfully completed during the period 2009–2013. The prototypes NEXT-DEMO (IFIC) and NEXT-DBDM (Berkeley) were built and operated for more than two years. These apparatuses have demonstrated the main features of the technology. The experiment is currently developing its second phase. The NEW detector is being constructed during 2014 and will operate in the LSC during 2015. The NEXT-100 detector will be built and commissioned during 2016 and 2017 and will start data taking in 2018. NEXT-100 could discover ββ0ν processes if the period of the decay is equal or less than 6×1025 year. The fourth phase of the experiment (BEXT) could start in 2020.

Results of the material screening program of the NEXT experiment

The Neutrino Experiment with a Xenon TPC (NEXT), intended to investigate neutrinoless double beta decay, requires extremely low background levels. An extensive material screening and selection process to assess the radioactivity of components is underway combining several techniques, including germanium γ-ray spectrometry performed at the Canfranc Underground Laboratory; recent results of this material screening program are presented here.

First Results of the LUX Dark Matter Experiment

LUX (Large Underground Xenon) is a dark matter direct detection experiment deployed at the 4850' level of the Sanford Underground Research Facility (SURF) in Lead, SD, operating a 370 kg dual-phase xenon TPC. Results of the first WIMP search run were presented in late 2013, for the analysis of 85.3 live-days with a fiducial volume of 118 kg, taken during the period of April to August 2013. The experiment exhibited a sensitivity to spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6×10−46cm2 at a WIMP mass of 33 GeV/c2, becoming the world's leading WIMP search result, in conflict with several previous claimed hints of discovery.

Improved background rejection in neutrinoless double beta decay experiments using a magnetic field in a high pressure xenon TPC

We demonstrate that the application of an external magnetic field could lead to an improved background rejection in neutrinoless double-beta (0νββ) decay experiments using a high-pressure xenon (HPXe) TPC. HPXe chambers are capable of imaging electron tracks, a feature that enhances the separation between signal events (the two electrons emitted in the 0νββ decay of 136Xe) and background events, arising chiefly from single electrons of kinetic energy compatible with the end-point of the 0νββ decay (0Qββ). Applying an external magnetic field of sufficiently high intensity (in the range of 0.5–1 Tesla for operating pressures in the range of 5-15 atmospheres) causes the electrons to produce helical tracks. Assuming the tracks can be properly reconstructed, the sign of the curvature can be determined at several points along these tracks, and such information can be used to separate signal (0νββ) events containing two electrons producing a track with two different directions of curvature from background (single-electron) events producing a track that should spiral in a single direction. Due to electron multiple scattering, this strategy is not perfectly efficient on an event-by-event basis, but a statistical estimator can be constructed which can be used to reject background events by one order of magnitude at a moderate cost (about 30%) in signal efficiency. Combining this estimator with the excellent energy resolution and topological signature identification characteristic of the HPXe TPC, it is possible to reach a background rate of less than one count per ton-year of exposure. Such a low background rate is an essential feature of the next generation of 0νββ experiments, aiming to fully explore the inverse hierarchy of neutrino masses.

First results of a large-area cryogenic gaseous photomultiplier coupled to a dual-phase liquid xenon TPC

We discuss recent advances in the development of cryogenic gaseous photomultipliers (GPM), for possible use in dark matter and other rare-event searches using noble-liquid targets. We present results from a 10 cm diameter GPM coupled to a dual-phase liquid xenon (LXe) TPC, demonstrating—for the first time—the feasibility of recording both primary (``S1'') and secondary (``S2'') scintillation signals. The detector comprised a triple Thick Gas Electron Multiplier (THGEM) structure with cesium iodide photocathode on the first element; it was shown to operate stably at 180 K with gains above 105, providing high single-photon detection efficiency even in the presence of large α particle-induced S2 signals comprising thousands of photoelectrons. S1 scintillation signals were recorded with a time resolution of 1.2 ns (RMS). The energy resolution (σ/E) for S2 electroluminescence of 5.5 MeV α particles was ∼ 9%, which is comparable to that obtained in the XENON100 TPC with PMTs. The results are discussed within the context of potential GPM deployment in future multi-ton noble-liquid detectors.

Cryogenic gaseous photomultipliers and liquid hole- multipliers: advances in THGEM-based sensors for future noble-liquid TPCs

Dual-phase noble-liquid TPCs are presently the most sensitive instruments for direct dark matter detection. Scaling up existing ton-scale designs to the multi-ton regime may prove to be technologically challenging. This includes both large-area coverage with affordable high-QE UV-photon detectors, and maintaining high precision in measuring the charge and light signals of rare events with keV-scale energy depositions. We present our recent advances in two complementary approaches to these problems: large-area cryogenic gaseous photomultipliers (GPM) for UV-photon detection, and liquid-hole multipliers (LHM) that provide electroluminescence light in response to ionization electrons and primary scintillation photons, using perforated electrodes immersed within the noble liquid. Results from a 10 cm diameter GPM coupled to a dual-phase liquid- xenon TPC demonstrate the feasibility of recording - for the first time - both primary (“S1”) and secondary (“S2”) scintillation signals, over a very broad dynamic range. The detector, comprising a triple-THGEM structure with CsI on the first element, has been operating stably at 180 K with gains larger than 105; it provided high single-photon detection efficiency - in the presence of massive alpha-particle induced S2 signals; S1 scintillation signals were recorded with time resolutions of 1.2 ns (RMS). Results with the LHM operated in liquid xenon yielded large photon gains, with a pulse-height resolution of 11% (RMS) for alpha-particle induced S2 signals. The detector response was stable over several months. The response of the S2 signals to rapid changes in pressure lead to the conclusion that the underlying mechanism for S2 light is electroluminescence in xenon bubbles trapped below the immersed THGEM electrode. Both studies have the potential of paving the way towards new designs of dual- and single-phase noble-liquid TPCs that could simplify the conception of future multi-ton detectors of dark matter and other rare events.

Characterization of Nuclear Recoils in High Pressure Xenon Gas: Towards a Simultaneous Search for WIMP Dark Matter and Neutrinoless Double Beta Decay

Xenon has recently been the medium of choice in several large scale detectors searching for WIMP dark matter and neutrinoless double beta decay. Though present-day large scale experiments use liquid xenon, the gas phase o_ers advantages favorable to both types of searches such as improved intrinsic energy resolution and fewer fluctuations in the partition of deposited energy between scintillation and ionization channels. We recently constructed a high pressure xenon gas TPC as a prototype for the NEXT (Neutrino Experiment with a Xenon TPC) neutrinoless double beta decay experiment and have demonstrated the feasibility of 0.5% FWHM energy resolution at the 136Xe double beta Q-value with 3-D tracking capabilities. We now present results from this prototype on the simultaneous observation of scintillation and ionization produced by nuclear recoils at approximately 14bar pressure. The recoils were produced by neutrons of approximately 2-6 MeV emitted from a radioisotope plutonium-beryllium source, and primary scintillation (S1) and electroluminescent photons produced by ionization (S2) were observed. We discuss the potential of gaseous xenon to distinguish between electron and nuclear recoils through the ratio of these two signals S2/S1. From these results combined with the possibility of using columnar recombination to sense nuclear recoil directionality at high pressures we envision a dual-purpose, ton-scale gaseous xenon detector capable of a combined search for WIMP dark matter and neutrinoless double beta decay. This work has been performed within the context of the NEXT collaboration.

R&D on a Fast LXe TPC with real-time event reconstruction

The FOXFIRE project (Feasibility Of a Xenon detector with Front-end for Ionization Real-time Extraction) aims at the realization of a Liquid Xenon TPC optimized for high rate particle physics experiments, in particular in the field of rare event searches, with particles in the 10–100MeV energy range. Liquid Xenon has several attractive properties to be exploited resulting in superior time and energy resolution, by using the scintillation light readout with suitable photo-detectors. A novel approach with a complementary TPC readout scheme can improve the space resolution to a level of a few hundred microns. We are studying both the feasibility of a light readout with higher granularity by means of Silicon PhotoMultipliers optimized for the Xenon emission spectrum as well as on an innovative micro-fabricated device capable of charge multiplication in liquid phase. The detector will be equipped with a readout electronics capable of online reconstruction of events, allowing the detector to sustain a high rate of interactions.

The trigger system in the NEXT-DEMO detector

NEXT-DEMO is a prototype of NEXT (Neutrino Experiment with Xenon TPC), an experiment to search for neutrino-less double beta decay using a 100 kg radio-pure, 90 % enriched (136Xe isotope) high-pressure gaseous xenon TPC with electroluminescence readout. The detector is based on a PMT plane for energy measurements and a SiPM tracking plane for topological event filtering. The experiment will be located in the Canfranc Underground Laboratory in Spain.Front-end electronics, trigger and data-acquisition systems (DAQ) have been built. The DAQ is an implementation of the Scalable Readout System (RD51 collaboration) based on FPGA. Our approach for trigger is to have a distributed and reconfigurable system in the DAQ itself. Moreover, the trigger allows on-line triggering based on the detection of primary or secondary scintillation light, or a combination of both, that arrives to the PMT plane.

The XENON100 experiment and the evolution to the ton scale

The XENON100 detector is a liquid xenon TPC dedicated to dark matter searches which is successfully operating in the Gran Sasso Laboratory of INFN. After the publication, in 2011, of the analysis of 100.2day of data, the experiment has been running in improved background conditions, collecting more than 200day of useful data, whose analysis will be unblinded in Summer 2012. In these proceedings, I will describe the main characteristics of the XENON100 detector. In the second part, I will describe the next generation XENON1T experiment, whose construction will begin in 2012.

Readout electronics for the SiPM tracking plane in the NEXT-1 prototype

NEXT is a new experiment to search for neutrinoless double beta decay using a 100kg radio-pure high-pressure gaseous xenon TPC with electroluminescence readout. A large-scale prototype with a SiPM tracking plane has been built. The primary electron paths can be reconstructed from time-resolved measurements of the light that arrives to the SiPM plane. Our approach is to measure how many photons have reached each SiPM sensor each microsecond with a gated integrator. We have designed and tested a 16-channel front-end board that includes the analog paths and a digital section. Each analog path consists of three different stages: a transimpedance amplifier, a gated integrator and an offset and gain control stage. Measurements show good linearity and the ability to detect single photoelectrons.

A liquid xenon TPC for a medical imaging Compton telescope

A new technique for medical imaging, “3γ imaging”, is studied by our group at SUBATECH for few years. A small liquid xenon time projection chamber prototype has been built in order to demonstrate the feasibility of this technique. With an ultra-low-noise front-end electronics, the energy deposit and resolution of 511keV γ-ray as a function of drift electric field (E) is measured with high precision. 500μm of z resolution is estimated by measuring the charge carriers drift velocity and time resolution.

A magnetically driven piston pump for ultra-clean applications

A magnetically driven piston pump for xenon gas recirculation is presented. The pump is designed to satisfy extreme purity and containment requirements, as is appropriate for the recirculation of isotopically enriched xenon through the purification system and large liquid xenon time projection chamber of EXO-200. The pump, using sprung polymer gaskets, is capable of pumping more than 16 standard liters per minute of xenon gas with 750 Torr differential pressure.