D. González-Díaz

First proof of topological signature in high pressure xenon gas with electroluminescence amplification

A bstractThe 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 Qββ. 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.

Present Status and Future Perspectives of the NEXT Experiment

NEXT is an experiment dedicated to neutrinoless double beta decay searches in xenon. The detector is a TPC, holding 100 kg of high-pressure xenon enriched in the 136Xe isotope. It is under construction in the Laboratorio Subterraneo de Canfranc in Spain, and it will begin operations in 2015. The NEXT detector concept provides an energy resolutionbetter than 1% FWHM and a topological signal that can be used to reduce the background. Furthermore, the NEXT technology can be extrapolated to a 1 ton-scale experiment.

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.

Radon and material radiopurity assessment for the NEXT double beta decay experiment

The Neutrino Experiment with a Xenon TPC (NEXT), intended to investigate the neutrinoless double beta decay using a high-pressure xenon gas TPC filled with Xe enriched in 136Xe at the Canfranc Underground Laboratory in Spain, requires ultra-low background conditions demanding an exhaustive control of material radiopurity and environmental radon levels. An extensive material screening process is underway for several years based mainly on gamma-ray spectroscopy using ultra-low background germanium detectors in Canfranc but also on mass spectrometry techniques like GDMS and ICPMS. Components from shielding, pressure vessel, electroluminescence and high voltage elements and energy and tracking readout planes have been analyzed, helping in the final design of the experiment and in the construction of the background model. The latest measurements carried out will be presented and the implication on NEXT of their results will be discussed. The commissioning of the NEW detector, as a first step towards NEXT, has started in Canfranc; in-situ measurements of airborne radon levels were taken there to optimize the system for radon mitigation and will be shown too.

Aging test of high rate MRPC

A new kind of low resistivity glass has been developed. Its volume resistivity is on the order of 10 10 Ωcm and MRPCs assembled with it show a very promising rate capability (>25 kHz/cm 2 ). This new detector has a very important range of application in high energy physics experiments such as FAIR-CBM, LHC-ATLAS or Jlab-SOLID, to mention some. In this paper we report new results related to its long-term behavior (ageing). The module has been irradiated by X-rays at a mips-equivalent flux of 15kHz/cm 2 , for 300 hours and for a released charge totaling 0.22C. No noticeable degradation could be observed. Compared to common glass MRPCs, the newly developed high rate counter responds faster to sudden irradiation.

Challenges for resistive gaseous detectors towards RPC2014

We present a summary of the status of the field of resistive gaseous detectors as discussed in a dedicated closing session that took place during the XI Workshop for Resistive Plate Chambers and Related Detectors held in Frascati, and especially we review the perspectives and ambitions of the community towards the XII Workshop to be held in Beijing in year 2014.

Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging

A new method to tag the barium daughter in the double-beta decay of ^{136}Xe is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba^{++}) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (∼2  nm), and detected with a statistical significance of 12.9σ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.

TREX-DM: a low background Micromegas-based TPC for low-mass WIMP detection

Dark Matter experiments are recently focusing their detection techniques in low-mass WIMPs, which requires the use of light elements and low energy threshold. In this context, we describe the TREX-DM experiment, a low background Micromegas-based TPC for low-mass WIMP detection. Its main goal is the operation of an active detection mass ~0.3 kg, with an energy threshold below 0.4 keVee and fully built with previously selected radiopure materials. This work describes the commissioning of the actual setup situated in a laboratory on surface and the updates needed for a possible physics run at the Canfranc Underground Laboratory (LSC) in 2016. A preliminary background model of TREX-DM is also presented, based on a Geant4 simulation, the simulation of the detectors response and two discrimination methods: a conservative muon/electron and one based on a neutron source. Based on this background model, TREX-DM could be competitive in the search for low-mass WIMPs. In particular it could be sensitive, e.g., to the low-mass WIMP interpretation of the DAMA/LIBRA and other hints in a conservative scenario.

Aging test of a real-size high rate MRPC for CBM-TOF wall

A new kind of low-resistivity glass has been developed. Its volume resistivity is on the order of 1010 Ω cm and multi-gap resistive plate chambers (MRPCs), once assembled with it, can be operated at a charged particle flux in excess of 25 kHz/cm2, with very small charge build-up at the plates. This new technology has a wide range of application in high energy physics experiments such as FAIR-CBM, LHC-ATLAS or Jlab-SOLID, to mention some. In this paper we report on results related to its long-term behavior (aging). A 6 × 2-pad CBM module has been irradiated by X-rays at a mips-equivalent flux of 15 kHz/cm2, for 300 hours and for a released charge totaling 0.22 C (50 mC/cm2). Tested in an electron beam before and after exposure, no degradation of the detector performances could be appreciated. As expected, compared to common glass MRPCs, the newly developed high rate counter also responds faster to sudden irradiation.

Production of long-strip multi-gap resistive plate chamber module for the STAR-MTD system

A new Long-strip Multi-gap Resistive Plate Chamber (LMRPC) prototype with 5 gas gaps has been developed for the Muon Telescope Detector (MTD) of the STAR experiment at RHIC in order to reduce the working High Voltage (HV) of previous design. Technical specifications related to the final infrastructure present in the experiment have motivated this effort. Its performance has been measured with cosmic rays. The efficiency of this prototype can reach 98% and the time resolution is around 95 ps. It shows a good uniformity among strips. The noise level is less than 0.2 Hz/cm2. The signal transmission and crosstalk of the modules was measured with a vector network analyzer, showing a good match with simulations within the amplifier bandwidth. A new cosmic-ray test system with long scintillators has been developed to accelerate the Quality Control (QC) process during the mass production of STAR-MTD. A selection of perpendicular cosmic-ray events for more accurate evaluation of the time resolution is achieved. The time resolution with this method is better, albeit with larger error, than the result obtained without any selection. A new spacer is used, resulting in a much reduced streamer ratio at comparable fields. Thirty-two modules have been built with the new spacer by the middle of April of 2012. They have been tested and they all have passed the QC.