Beta Decay Of 136Xe Research Articles

Demonstration of neutrinoless double beta decay searches in gaseous xenon with NEXT

The NEXT experiment aims at the sensitive search of the neutrinoless double beta decay in 136Xe, using high-pressure gas electroluminescent time projection chambers. The NEXT-White detector is the first radiopure demonstrator of this technology, operated in the Laboratorio Subterráneo de Canfranc. Achieving an energy resolution of 1% FWHM at 2.6 MeV and further background rejection by means of the topology of the reconstructed tracks, NEXT-White has been exploited beyond its original goals in order to perform a neu- trinoless double beta decay search. The analysis considers the combination of 271.6 days of 136Xe-enriched data and 208.9 days of 136Xe-depleted data. A detailed background modeling and measurement has been developed, ensuring the time stability of the radiogenic and cosmogenic contributions across both data samples. Limits to the neutrinoless mode are obtained in two alternative analyses: a background-model-dependent approach and a novel direct background-subtraction technique, offering results with small dependence on the background model assumptions. With a fiducial mass of only 3.50 ± 0.01 kg of 136Xe-enriched xenon, 90% C.L. lower limits to the neutrinoless double beta decay are found in the T1/20ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {T}_{1/2}^{0\ u } $$\\end{document} > 5.5 × 1023− 1.3 × 1024 yr range, depending on the method. The presented techniques stand as a proof-of-concept for the searches to be implemented with larger NEXT detectors.

Rapid characterization of silicon photomultipliers for noble liquid experiments

Silicon photomultipliers (SiPMs) are emerging as the photodetector technology to be used in upcoming noble liquid experiments. Newly developed SiPMs sensitive to vacuum ultraviolet (VUV) light will be directly used for the readout of scintillation photons (λ = 175 nm) from liquid xenon in future tonne-scale experiments, such as nEXO, searching for neutrinoless double beta decay in 136Xe. In this research project, VUV-SiPMs from two different vendors are characterized using current–voltage (IV) and pulse-level measurements performed at TRIUMF, from room temperature to liquid xenon temperature. These data are analysed to extract the SiPM’s features such as breakdown voltage, gain, crosstalk, afterpulsing and dark noise rates. The IV and pulse-level results are compared. A method is proposed for rapid quality control of large numbers of SiPM using IV measurements.

The NEXT experiment for neutrinoless double beta decay searches

The goal of the NEXT experiment is the observation of the neutrinoless double beta decay in 136Xe using a gaseous xenon TPC with electroluminescent amplification and specialized photodetector arrays for calorimetry and tracking. After a prototyping period (2009-2014) where the technique was demonstrated, the Collaboration has completed the construction and started the operation of its first phase (NEXT-White or NEW) in the Laboratorio Subterraneo de Canfranc, in the Spanish Pyrenees, with the objectives of measuring in-situ the NEXT background model and the two-neutrino mode of the double beta decay under a radiopure regime. After running NEW, the Collaboration will operate a bigger detector, NEXT-100, which will look for the neutrinoless decay mode.

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.

Event reconstruction in NEXT using the ML-EM algorithm

The NEXT collaboration aims to find the neutrinoless double beta decay in 136Xe. The rareness of this decay demands an exceptional background rejection. This can be obtained with an excellent energy resolution, which has been already demonstrated in the NEXT prototypes. In addition to this, the ββ0ν decay in gas produces a characteristic topological signal which could be an extremely useful extra handle to avoid background events.The need for a satisfactory topology reconstruction has led the NEXT Collaboration to implement the Maximum Likelihood Expectation Maximization method (ML-EM) in the data processing scheme. ML-EM is a generic iterative algorithm for many kinds of inverse problems. Although this method is well known in medical imaging and has been used widely in Positron Emission Tomography, it has never been applied to a time projection chamber. First results and studies of the performance of the method will be presented in this poster.

First proof of topological signature in the high pressure xenon gas TPC with electroluminescence amplification for the NEXT experiment

The NEXT experiment aims to observe the neutrinoless double beta decay of 136Xe in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. One of the main advantages of this technology is the possibility to reconstruct the topology of events with energies close to Q ββ . This paper presents the first demonstration that the topology provides extra handles to reject background events using data obtained with the NEXT-DEMO prototype. Single electrons resulting from the interactions of 22Na 1275 keV gammas and electronpositron pairs produced by conversions of gammas from the 228Th decay chain were used to represent the background and the signal in a double beta decay. These data were used to develop algorithms for the reconstruction of tracks and the identification of the energy deposited at the end-points, providing an extra background rejection factor of 24.3 ± 1.4 (stat.)%, while maintaining an efficiency of 66.7 ± 1.% for signal events.

Search for neutrino-less double beta decay with EXO-200 and prospects for Ba ion tagging

The Enriched Xenon Observatory collaboration searches for neutrino-less double beta decay in 136Xe. The first phase of the experiment, EXO-200 has started taking data in 2011 and has already produced important physics results like the first observation of the allowed two-neutrino double beta decay in 136Xe. A massive effort for material screening has accompanied the design of EXO-200 and has produced a detector with very low background due to the residual radioactivity. The most recent data analysis campaign has provided a strong limit for the neutrino-less double beta decay in 136Xe. For the next phase ton-scale detector, the collaboration is investigating the options for employing a Ba ion tagging technique to provide complete suppression of the radioactive background.

Results from the NEXT prototypes

NEXT-100 is an electroluminescent high pressure Time Projection Chamber currently under construction. It will search for the neutrino-less double beta decay in 136Xe at the Canfranc Underground Laboratory. NEXT-100 aims to achieve nearly intrinsic energy resolution and to highly suppress background events by taking advantage of the unique properties of xenon in the gaseous phase as the detection medium. In order to prove the principle of operation and to study which are the best operational conditions, two prototypes were constructed: NEXT-DEMO and NEXT-DBDM. In this paper we present the latest results from both prototypes. We report the improvement in terms of light collection (~ 3×) achieved by coating the walls of NEXT-DEMO with tetraphenyl butadiene (TPB), the outstanding energy resolution of 1 % (Full Width Half Maximum) from NEXT-DBDM as well as the tracking capabilities of this prototype (2.1 mm RMS error for point-like depositions) achieved by using a square array of 8 × 8 SiPMs.

NEXT prototypes based on micromegas

The NEXT experiment searches for neutrinoless double beta decay in 136Xe in a high pressure TPC. The detector is based on electroluminescence light measured with PMT's and SiPM's. In parallel with this baseline, a R&D program based on micromegas (MMs) detectors with pixelized anode is developed as an option to detect both energy and topology of the signals. MMs are considered as a readout for TPCs in the field of rare event searches (dark matter, axions or double beta decay). They are a good option for such experiments because of their high radiopurity, robustness and good performance regarding energy resolution and pattern recognition. In the R&D line, prototypes chambers based on micromegas were constructed to study their properties at different pressures and gas mixtures and also to test microbulk micromegas in conditions where electron tracks could be fully contained. The results on the commissioning and performance of these prototypes are here presented.

GraXe, graphene and xenon for neutrinoless double beta decay searches

We propose a new detector concept, GraXe (to be pronounced as grace), to search for neutrinoless double beta decay in 136XE. GraXe combines a popular detection medium in rare-event searches, liquid xenon, with a new, background-free material, graphene.In our baseline design of GraXe, a sphere made of graphene-coatedtitanium mesh and filled with liquid xenon (LXe) enriched in the136XE isotope is immersed in a large volume of natural LXe instrumentedwith photodetectors. Liquid xenon is an excellent scintillator,reasonably transparent to its own light. Graphene is transparent overa large frequency range, and impermeable to the xenon. Event positioncould be deduced from the light pattern detected in thephotosensors. External backgrounds would be shielded by the buffer ofnatural LXe, leaving the ultra-radiopure internal volume virtuallyfree of background.Industrial graphene can be manufactured at a competitive cost toproduce the sphere. Enriching xenon in the isotope 136XE is easy andrelatively cheap, and there is already near one ton of enriched xenonavailable in the world (currently being used by the EXO, KamLAND-Zenand NEXT experiments). All the cryogenic know-how is readily availablefrom the numerous experiments using liquid xenon. An experiment usingthe GraXe concept appears realistic and affordable in a short timescale, and its physics potential is enormous.

Can the "intrinsic" energy resolution in xenon be surpassed?

Energy resolution is determined by fluctuations in the transformation of deposited energy to ionization and excitation. For noble gases, adding a molecular impurity that introduces a strong Penning effect reduces the Fano factor, improving energy resolution. I show that in xenon, adding trimethylamine (TMA) may provide a strong Penning effect and also permit electroluminescence (EL) at wavelengths characteristic of TMA. This combination may permit a large TPC to be operated with better than "intrinsic" energy resolution in the search for neutrino-less double beta decay in 136Xe. This path is being explored within the context of the NEXT collaboration.

The NEXT experiment: neutrinoless double beta decay searches at the LSC

NEXT is a proposed 100-kg high-pressure xenon gas TPC that will search for neutrinoless double beta decay in 136Xe. Such a detector, thanks to its excellent energy resolution and its powerful background rejection provided by the distinct double beta decay topological signature, may become one of the leading experiments of the field. The project is proceeding through a fast research and development phase. The first prototypes, containing about 1 kg of pressurized xenon will be taking data in 2010, and the final detector, NEXT-100, is planned to run in late 2013 at the Laboratorio Subterráneo de Canfranc (LSC), Spain.

Searching for double beta decay with the Enriched Xenon Observatory

The Enriched Xenon Observatory (EXO) will search for neutrinoless double beta decay in 136Xe. The first phase of the experiment, EXO-200, uses 200 kg of liquid xenon enriched to 80% in 136Xe in an ultra-low background time projection chamber (TPC). EXO-200 is in the final stages of assembly at the WIPP site in Carlsbad, NM and will begin taking data in 2009 with two-year sensitivity to the half-life for neutrinoless double beta decay of 6.4 × 1025 years. According to nuclear matrix element calculations, this corresponds to an effective Majorana neutrino mass of 0.13 to 0.19 eV. The EXO collaboration is also performing R&D for simultaneous detection of the decay electrons and emerging Ba ion allowing essentially background free detection in a future, ton-scale detector. The status of EXO-200 and of the ion tagging technology in liquid xenon is described.

New gas mixtures suitable for rare event detectionusing a Micromegas-TPC detector

The aim of the presented work was to develop furthertechniques based on a Micromegas-TPC, in order to reach a high gasgain with good energy resolution, and to search for gas mixturessuitable for rare event detection. This paper focuses on Xenon,which is convenient for the search of neutrinoless double betadecay in 136Xe, and CF4, suitable for dark matter searchesand the study of solar and reactor neutrinos. Variousconfigurations of the Micromegas plane were investigated and aredescribed. Gains of 105 and energy resolutions of 35–65%at 6 keV have been achieved.

Micromegas-TPC development for rare event detection

We present some important results related to Micromegas-TPC development for rare event detection:First, we show the influence of the detection plane structure on the energy resolution, where, replacing the wires planes (MWPC) by the Micromegas micropattern, gave a high collection efficiency with good uniformity and good energy resolution.Second, we prove that the increase of the height of the amplification zone permits a good charge collection at higher gas pressure.Third, we present a new gas mixture ‘‘Xe(98)CF4(2)’’, which is convenient for the search of neutrinoless double beta decay in 136Xe.Fourth, large size Micromegas, with 50 cm of diameter is operated in the Gotthard-TPC (200 l) and showed high effciency and good energy resolution with low energy sources.

Search for ββ decay in 136Xe: new results from the Gotthard experiment

The Gotthard Xe experiment has taken an additional 6013 hours of data with an upgraded readout system. Lower limits for the half-life of the double beta decay in 136Xe are T 1/2 0 ν >4.4×10 23 yr (including 6830 hours taken in an earlier phase), T 1/2 0 νχ 0 >0.72×10 22 yr and T 1/2 2 ν >3.6×10 20 yr at 90% confidence level. Alpha spectroscopy, as well as βα and αα coincidence techniques lead to a determination of the activity of the gas of 10 −12 g/g effective of 232Th and 238U. Evaluations of background strongly suggest that an appreciable fraction of the ββ-candidates comes from the allowed 2 ν decay.

New limits on double beta decay of 136Xe

A Xenon TPC with an active volume of 180 liters has been built to study the neutrinoless double beta decay in 136Xe. Data were taken in the Gotthard Underground Laboratory with 5 atm of xenon enriched to 62% in 136Xe. A total of 7647 hours of data has been taken. New limits on neutrino mass and majoron decay are presented.

Event identification with a time projection chamber in a double beta decay experiment on 136Xe

A xenon time projection chamber has been constructed to study double beta decay in 136Xe. The excellent track reconstruction capability of the TPC provides a powerful means of background identification. We have demonstrated the novel technique of measuring the directionality of low energy (MeV range) electrons by the difference of dE dx between their beginnings and ends. Rejection efficiencies are 100% for alpha particles, cosmic muons and multiple Compton scattering, and more than 98% for single electrons, while the identification efficiencies for events due to neutrinoless double beta decay are 76% and 65% for the mass mechanism and right-handed currents modes, respectively. Very sensitive limit has been achieved for the half-life of the 0νββ channel. The tracking performance of the TPC as well as the event analysis and background rejection procedures of the experiment are discussed.

New limits on double beta decay of 136Xe

A Xenon TPC with an active volume of 207 liters has been built to study the neutrinoless double beta decay in 136Xe. Data were taken in the Gotthard Underground Laboratory with 5 atm of xenon enriched to 62.5% in 136Xe. A total of 6830 hours of data has been taken. New limits on neutrino mass and majoron decay are presented.

Project for detecting the double beta decay of136Xe

For detecting the nuclear double beta decay of136Xe, a liquid-xenon positive-ion collector and a time-of-flight mass spectrometer are under development for detecting the decay product136Ba. Two sets of lasers are used with the mass spectrometer. An Nd-YAG laser is used for sampling136Ba from the surface of the positive-ion collector electrode, and a dye laser pumped by an Nd-YAG laser is used for the selective ionization of136Ba. The principle of measurements as well as the experimental apparatus and procedures are described in detail, together with our future plans.