Search

[EN] Convolutional neural networks (CNNs) are widely used state-of-the-art computer vision tools that are becoming increasingly popular in high-energy physics. In this paper, we attempt to understand the potential of CNNs for event classification in the NEXT experiment, which will search for neutrinoless double-beta decay in Xe-136. To do so, we demonstrate the usage of CNNs for the identification of electron-positron pair production events, which exhibit a topology similar to that of a neutrinoless double-beta decay event. These events were produced in the NEXT-White high-pressure xenon TPC using 2.6 MeV gamma rays from a Th-228 calibration source. We train a network on Monte Carlo-simulated events and show that, by applying on-the-fly data augmentation, the network can be made robust against differences between simulation and data. The use of CNNs offers significant improvement in signal efficiency and background rejection when compared to previous non-CNN-based analyses, This study used computing resources from Artemisa, co-funded by the European Union through the 2014-2020 FEDER Operative Programme of the Comunitat Valenciana, project DIFEDER/2018/048. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357. The NEXT collaboration acknowledges support from the following agencies and institutions: Xunta de Galicia (Centro singularde investigacion de Galicia accreditation 2019-2022), by European Union ERDF, and by the "Maria de Maeztu" Units of Excellence program MDM-2016-0692 and the Spanish Research State Agency"; the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad and the Ministerio de Ciencia, Innovacion y Universidades of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program grants SEV-20140398 and CEX2018-000867-S; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014 and under projects UID/FIS/04559/2020 to fund the activities of LIBPhys-UC; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and DE-SC0019223/DE SC0019054 (University of Texas at Arlington); and the University of Texas at Arlington. DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC-2015 18820. JMA acknowledges support from Fundacion Bancaria "la Caixa" (ID 100010434), grant code LCF/BQ/PI19/11690012. We also warmly acknowledge the Laboratori Nazionali del Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.

PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel concept for positron emission tomography scanners, which uses liquid xenon as a scintillation medium and silicon photomultipliers as a readout. The large scintillation yield and the fast scintillation time of liquid xenon, as well as its scalability, makes it an excellent candidate for PET scanners with Time-of-Flight measurements, especially for total-body machines. A first prototype of PETALO is fully operating, devoted to demonstrate the potential of the concept, measuring the energy and time resolution and to test technical solutions for a complete ring. The prototype consists of an aluminum box filled with liquid xenon, with two arrays of SiPMs on opposite sides facing the xenon. A $\beta$+ emitter source generating 511-keV pairs of gammas is placed in a central port and the SiPMs record the scintillation light produced by the gamma interactions, allowing for the reconstruction of the position, the energy and the time of the interactions., Comment: Proceedings of LIDINE 2021: LIght Detection in Noble Elements, 14-18 September 2021, University of California San Diego

The NEXT collaboration: et al., Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of ∼ 1027 yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of ∼ 5 when reconstructing electron-positron pairs in the 208Tl 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterráneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of ∼ 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e−e+ pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.

[EN] Double electron capture by proton-rich nuclei is a second-order nuclear process analogous to double beta decay. Despite their similarities, the decay signature is quite di erent, potentially providing a new channel to measure the hypothesized neutrinoless mode of these decays. The Standard-Model-allowed two-neutrino double electron capture has been predicted for a number of isotopes, but only observed in 78Kr, 130Ba and, recently, 124Xe. The sensitivity to this decay establishes a benchmark for the ultimate experimental goal, namely the potential to discover also the lepton-number-violating neutrinoless version of this process. Here we report on the current sensitivity of the NEXT-White detector to 124Xe 2 ECEC and on the extrapolation to NEXT-100. Using simulated data for the 2 ECEC signal and real data from NEXT-White operated with 124Xe-depleted gas as background, we de ne an optimal event selection that maximizes the NEXT-White sensitivity. We estimate that, for NEXT-100 operated with xenon gas isotopically enriched with 1 kg of 124Xe and for a 5-year run, a sensitivity to the two-neutroni double electron capture half-life of 6x10exp22 years (at 90% con dence level) or better can be reached., The NEXT collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad and the Ministerio de Ciencia, Innovacion y Universidades of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program grants SEV-2014-0398 and CEX2018-000867-S, and the Maria de Maeztu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014, under project UID/FIS/04559/2013 to fund the activities of LIBPhys, and under grants PD/BD/105921/2014, SFRH/BPD/109180/2015 and SFRH/BPD/76842/2011; the U.S. Department of Energy under contracts number DE-AC02-06CH11357 (Argonne National Laboratory), DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and DE-SC0019223/DE-SC0019054 (University of Texas at Arlington); and the University of Texas at Arlington. DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC-2015-18820. We also warmly acknowledge the Laboratori Nazionali del Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment

[EN] Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. However, the reflectance of PTFE is a function of its thickness. In this work, we investigate this dependence in air for light of wavelengths 260 nm and 450 nm using two complementary methods. We find that PTFE reflectance for thicknesses from 5 mm to 10 mm ranges from 92.5% to 94.5% at 450 nm, and from 90.0% to 92.0% at 260 nm We also see that the reflectance of PIFE of a given thickness can vary by as much as 2.7% within the same piece of material. Finally, we show that placing a specular reflector behind the PTFE can recover the loss of reflectance in the visible without introducing a specular component in the reflectance., The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad and the Ministerio de Ciencia, Innovacion y Universidades of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program grants SEV-2014-0398 and CEX2018-000867-S, and the Maria de Maeztu Program MDM-2016-0692; the Generalitat Valenciana under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014 and under projects UID/04559/2020 to fund the activities of LIBPhys-UC; the U.S. Department of Energy under contracts No. DE-AC02-06CH11357 (Argonne National Laboratory), DE-AC0207CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and DE-SC0019223/DE-SC0019054 (University of Texas at Arlington); and the University of Texas at Arlington (USA). DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC2015-18820. JM-A acknowledges support from Fundacion Bancaria "la Caixa" (ID 100010434), grant code LCF/BQ/PI19/11690012. Finally, we thank Brendon Bullard, Paolo Giromini and Neeraj Tata for helpful discussions and assistance with preliminary measurements.

The European Spallation Source (ESS), presently well on its way to completion, will soon provide the most intense neutron beams for multi-disciplinary science. Fortuitously, it will also generate the largest pulsed neutrino flux suitable for the detection of Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS), a process recently measured for the first time at ORNL's Spallation Neutron Source. We describe innovative detector technologies maximally able to profit from the order-of-magnitude increase in neutrino flux provided by the ESS, along with their sensitivity to a rich particle physics phenomenology accessible through high-statistics, precision CE$\nu$NS measurements., Comment: 21 pages, 15 figures. v2: Minor changes, typo corrected in Fig 6. Version accepted for publication in JHEP

PETALO (Positron Emission TOF Apparatus based on Liquid xenOn) exploits the unique characteristics of liquid xenon as a scintillator for use in a PET detector. Here initial simulation studies are detailed which highlight the potential of such a detector and outline the steps taken in the reconstruction of 511 keV gamma rays and in the full PET image reconstruction. In particular, a neural network-based approach is conceived in order to tag gamma rays that are poorly reconstructed due to Compton scattering. It is found that though a significant fraction of events undergo Compton scattering, not all of these events will necessarily be poorly reconstructed. Further study is necessary to determine whether or not an online implementation of the neural network-based event tagging will provide sufficient recovery of the image quality., Presented at the 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference

Motivated by the possibility of guiding daughter ions from double beta decay events to single-ion sensors for barium tagging, the NEXT collaboration is developing a program of R&D to test radio frequency (RF) carpets for ion transport in high pressure xenon gas. This would require carpet functionality in regimes at higher pressures than have been previously reported, implying correspondingly larger electrode voltages than in existing systems. This mode of operation appears plausible for contemporary RF-carpet geometries due to the higher predicted breakdown strength of high pressure xenon relative to low pressure helium, the working medium in most existing RF carpet devices. In this paper we present the first measurements of the high voltage dielectric strength of xenon gas at high pressure and at the relevant RF frequencies for ion transport (in the 10 MHz range), as well as new DC and RF measurements of the dielectric strengths of high pressure argon and helium gases at small gap sizes. We find breakdown voltages that are compatible with stable RF carpet operation given the gas, pressure, voltage, materials and geometry of interest.

Within the framework of xenon-based double beta decay experiments, we propose the possibility to improve the background rejection of an electroluminescent Time Projection Chamber (EL TPC) by reducing the diffusion of the drifting electrons while keeping nearly intact the energy resolution of a pure xenon EL TPC. Based on state-of-the-art microscopic simulations, a substantial addition of helium, around 10 or 15~\%, may reduce drastically the transverse diffusion down to 2.5~mm/$\sqrt{\mathrm{m}}$ from the 10.5~mm/$\sqrt{\mathrm{m}}$ of pure xenon. The longitudinal diffusion remains around 4~mm/$\sqrt{\mathrm{m}}$. Light production studies have been performed as well. They show that the relative variation in energy resolution introduced by such a change does not exceed a few percent, which leaves the energy resolution practically unchanged. The technical caveats of using photomultipliers close to an helium atmosphere are also discussed in detail., 8 pages, 7 figures

We report new measurements of the drift velocity and longitudinal diffusion coefficients of electrons in pure xenon gas and in xenon-helium gas mixtures at 1-9 bar and electric field strengths of 50-300 V/cm. In pure xenon we find excellent agreement with world data at all $E/P$, for both drift velocity and diffusion coefficients. However, a larger value of the longitudinal diffusion coefficient than theoretical predictions is found at low $E/P$ in pure xenon, below the range of reduced fields usually probed by TPC experiments. A similar effect is observed in xenon-helium gas mixtures at somewhat larger $E/P$. Drift velocities in xenon-helium mixtures are found to be theoretically well predicted. Although longitudinal diffusion in xenon-helium mixtures is found to be larger than anticipated, extrapolation based on the measured longitudinal diffusion coefficients suggest that the use of helium additives to reduce transverse diffusion in xenon gas remains a promising prospect.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM, The NEXT experiment aims at searching for the hypothetical neutrinoless double-beta decay from the 136Xe isotope using a high-purity xenon TPC. Efficient discrimination of the events through pattern recognition of the topology of primary ionisation tracks is a major requirement for the experiment. However, it is limited by the diffusion of electrons. It is known that the addition of a small fraction of a molecular gas to xenon reduces electron diffusion. On the other hand, the electroluminescence (EL) yield drops and the achievable energy resolution may be compromised. We have studied the effect of adding several molecular gases to xenon (CO2, CH4 and CF4) on the EL yield and energy resolution obtained in a small prototype of driftless gas proportional scintillation counter. We have compared our results on the scintillation characteristics (EL yield and energy resolution) with a microscopic simulation, obtaining the diffusion coefficients in those conditions as well. Accordingly, electron diffusion may be reduced from about 10 mm/m for pure xenon down to 2.5 mm/m using additive concentrations of about 0.05%, 0.2% and 0.02% for CO2, CH4 and CF4, respectively. Our results show that CF4 admixtures present the highest EL yield in those conditions, but very poor energy resolution as a result of huge fluctuations observed in the EL formation. CH4 presents the best energy resolution despite the EL yield being the lowest. The results obtained with xenon admixtures are extrapolated to the operational conditions of the NEXT-100 TPC. CO2 and CH4 show potential as molecular additives in a large xenon TPC. While CO2 has some operational constraints, making it difficult to be used in a large TPC, CH4 shows the best performance and stability as molecular additive to be used in the NEXT-100 TPC, with an extrapolated energy resolution of 0.4% at 2.45 MeV for concentrations below 0.4%, which is only slightly worse than the one obtained for pure xenon. We demonstrate the possibility to have an electroluminescence TPC operating very close to the thermal diffusion limit without jeopardizing the TPC performance, if CO2 or CH4 are chosen as additives.[Figure not available: see fulltext.], The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union’s Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Skłodowska-Curie Grant Agreements No.674896, 690575 and 740055; the Ministerio de Economía y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the María de Maetzu Program MDM-2016-0692;the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014, under project UID/FIS/04559/2013 to fund the activities of LIBPhys, and under grants PD/BD/105921/2014, SFRH/BPD/109180/2015 and SFRH/BPD/76842/2011; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020(Texas A&M) and DE-SC0017721 (University of Texas at Arlington); and the University of Texas at Arlington. DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC-2015-18820. We also warmly acknowledge the Laboratori Nazionalidel Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coatingof various parts of the NEXT-White TPC.

[EN] Conceived to host 5 kg of xenón at a pressure of 15 bar in the ¿ducial volume,the NEXTWhite (NEW)apparatus is currently the largest high pressure xenon gas TPC using electroluminescent ampli¿cation in the world. It is also a 1:2 scale model of the NEXT-100 detector scheduled to start searching for ßß0¿ decays in 136Xe in 2019. Both detectors measure the energy of the event using a plane of photomultipliers located behind a transparent cathode. They can also reconstruct the trajectories of charged tracks in the dense gas of the TPC with the help of a plane of silicon photomultipliers located behind the anode. A sophisticated gas system, common to both detectors, allows the high gas purity needed to guarantee a long electron lifetime. NEXT-White has been operating since October 2017 at the Canfranc Underground Laboratory (LSC), in Spain. This paper describes the detector and associated infrastructures., The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the Maria de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT and FEDER through the program COMPETE, projects PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contract numbers DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M), DE-SC0017721 (University of Texas at Arlington), and DE-AC02-06CH11357 (Argonne National Laboratory); and the University of Texas at Arlington. We also warmly acknowledge the Laboratorio Nazionale di Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.

[EN] Xe-136 is used as the target medium for many experiments searching for 0 nu beta beta. Despite underground operation, cosmic muons that reach the laboratory can produce spallation neutrons causing activation of detector materials. A potential background that is difficult to veto using muon tagging comes in the form of Xe-137 created by the capture of neutrons on Xe-136. This isotope decays via beta decay with a half-life of 3.8 min and a Q(beta) of similar to 4.16 MeV. This work proposes and explores the concept of adding a small percentage of He-3 to xenon as a means to capture thermal neutrons and reduce the number of activations in the detector volume. When using this technique we find the contamination from Xe-137 activation can be reduced to negligible levels in tonne and multi-tonne scale high pressure gas xenon neutrinoless double beta decay experiments running at any depth in an underground laboratory., The work described was supported by the Department of Energy under Award numbers DE-SC0019054 and DE-SC0019223. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Program for Research and Innovation Horizon 2020 (2014-2020) under the Marie Skodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the Maria de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014, under project UID/FIS/04559/2013 to fund the activities of LIBPhys, and under grants PD/BD/105921/2014, SFRH/BPD/109180/2015 and SFRH/BPD/76842/2011. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.

PETALO (a Positron Emission Tof Apparatus based on Liquid xenOn) is a new approach for Positron Emission Tomography scanners, based on liquid xenon. The PETALO detector aims at capturing the light produced by the scintillation in LXe taking advantage of its uniform response and continuity. This strategy will lead to a geometrical distortion free behavior compared to other PET detectors. To this end, the sensors chosen for the light readout are SiPMs, which provide large area, high gain and very low noise. In order to take advantage of the unique PETALO detector characteristics a read-out architecture must be designed to meet the following specifications: Electronics associated to detector (front-end and read-out itself) must be fully expandable in terms of detector size. Read-out scheme must be compatible with the non-segmented structure of the detector. Time of Flight (TOF) capabilities must be assured at the scanner level, that is to say front-end and read-out electronics should not degrade LXe time performance. In these proceedings, a new readout concept is introduced which is compatible with a fully continuous medium detector such as PETALO. Results show that the system is feasible, with the introduction of a fast compression technique to further reduce the data bandwidth requirements.

One of the major goals of the NEXT-White (NEW) detector is to demonstrate the energy resolution that an electroluminescent high pressure xenon TPC can achieve for high energy tracks. For this purpose, energy calibrations with 137Cs and 232Th sources have been carried out as a part of the long run taken with the detector during most of 2017. This paper describes the initial results obtained with those calibrations, showing excellent linearity and an energy resolution that extrapolates to approximately 1% FWHM at Q$_{\beta\beta}$., Comment: 14 pages, 8 figures, Accepted for publication in JINST

High pressure gas time projection chambers (HPGTPCs) are made with a variety of materials, many of which have not been well characterized in high pressure noble gas environments. As HPGTPCs are scaled up in size toward ton-scale detectors, assemblies become larger and more complex, creating a need for detailed understanding of how structural supports and high voltage insulators behave. This includes the identification of materials with predictable mechanical properties and without surface charge accumulation that may lead to field deformation or sparking. This paper explores the mechanical and electrical effects of high pressure gas environments on insulating polymers PTFE, HDPE, PEEK, POM and UHMW in Argon and Xenon, including studying absorption, swelling and high voltage insulation strength., Prepared for JINST v2: Fix initial submit problem v3: Submitted to journal

The measurement of the internal $^{222}$Rn activity in the NEXT-White detector during the so-called Run-II period with $^{136}$Xe-depleted xenon is discussed in detail, together with its implications for double beta decay searches in NEXT. The activity is measured through the alpha production rate induced in the fiducial volume by $^{222}$Rn and its alpha-emitting progeny. The specific activity is measured to be $(38.1\pm 2.2~\mathrm{(stat.)}\pm 5.9~\mathrm{(syst.)})$~mBq/m$^3$. Radon-induced electrons have also been characterized from the decay of the $^{214}$Bi daughter ions plating out on the cathode of the time projection chamber. From our studies, we conclude that radon-induced backgrounds are sufficiently low to enable a successful NEXT-100 physics program, as the projected rate contribution should not exceed 0.1~counts/yr in the neutrinoless double beta decay sample., Comment: 28 pages, 10 figures, 6 tables. Version accepted for publication in JHEP

The fast scintillation decay time and the high scintillation yield of liquid xenon makes it an appropriate material for nuclear medicine. Moreover, being a continuous medium with a uniform response, liquid xenon allows one to avoid most of the geometrical distortions of conventional detectors based on scintillating crystals. In this paper, we describe how these properties have motivated the development of a novel concept for positron emission tomography scanners with Time-Of-Flight measurement, which uses liquid xenon as a scintillating material and silicon photomultipliers as sensors. Monte Carlo studies have indicated that this technology would provide a very good intrinsic time resolution, of around 70 ps. Moreover, being liquid xenon transparent to UV and blue wavelengths, both scintillation and Cherenkov light can be exploited. While the former can be used for energy measurements, the latter is a prompt signal (of a few picoseconds), which provides a very precise time measurement. Monte Carlo simulations point to a time resolution of 30-50 ps obtained using Cherenkov light. A first prototype is being built to demonstrate the high energy, spatial and time resolution of this concept, using a ring of around 30 cm of internal diameter and a depth of 3 cm instrumented with VUV--sensitive silicon photomultipliers., Comment: arXiv admin note: text overlap with arXiv:1712.05751

[EN] Gaseous time projection chambers (TPC) are a very attractive detector technology for particle tracking. Characterization of both drift velocity and di¿usion is of great importance to correctly assess their tracking capabilities. NEXT-White is a High Pressure Xenon gas TPC with electroluminescent ampli¿cation, a 1:2 scale model of the future NEXT-100detector, which will be dedicated to neutrinoless double beta decay searches. NEXT-White has been operating at Canfranc Underground Laboratory (LSC) since December2016. The drift parameters have been measured using 83mKr for a range of reduced drift ¿elds at two di¿erent pressure regimes, namely 7.2 bar and 9.1 bar. Theresults have been compared with Magboltz simulations. Agreement at the 5% level or better has been found for drift velocity, longitudinal di¿usion and transverse di¿usion., The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the Maria de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT and FEDER through the program COMPETE, projects PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and de-sc0017721 (University of Texas at Arlington); and the University of Texas at Arlington. We also warmly acknowledge the Laboratorio Nazionale di Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.

NEXT (Neutrino Experiment with a Xenon TPC) aims to observe the neutrinoless double beta decay of \ensuremath{{}^{136}\rm Xe} in a high-pressure gas xenon Time Projection Chamber using electroluminescence to amplify the signal from ionization. The two main advantages of this technology are a high energy resolution and the possibility of reconstructing electron tracks. NEXT-100 is an electroluminescent, asymmetric TPC which will host 100 kg of the \ensuremath{{}^{136}\rm Xe} isotope at 15 bar of pressure. On one side, a sparse array of photomultipliers records both the primary scintillation signal, which gives the starting time of the event, and electroluminescence, which gives a precise measurement of the total deposited energy. On the other side, a dense grid of silicon photomultipliers provides the reconstruction of the electron tracks. Being able to reconstruct the position of a track is doubly useful: on the one hand, it allows the correction of the energy of the event, which varies according to position, and on the other hand it provides an extra handle for background rejection, since a two-electron track shows higher energy density at both ends, while a single-electron track only at one end. After a prototyping period (2009-2014) NEXT has completed the construction and started the operation of its first phase (NEW) in the Laboratorio Subterr\'aneo de Canfranc, in the Spanish Pyrenees, with the objectives of measuring the NEXT background model and the two-neutrino mode of the double beta decay., Comment: Proceedings of EPS-HEP 2017, Venice (Italy), July 2017

[EN] The "Neutrino Experiment with a Xenon Time-Projection Chamber" (NEXT) experiment intends to investigate the neutrinoless double beta decay of 136Xe, and therefore requires a severe suppression of potential backgrounds. An extensive material screening and selection process was undertaken to quantify the radioactivity of the materials used in the experiment. Separate energy and tracking readout planes using different sensors allow us to combine the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. The design of radiopure readout planes, in direct contact with the gas detector medium, was especially challenging since the required components typically have activities too large for experiments demanding ultra-low background conditions. After studying the tracking plane, here the radiopurity control of the energy plane is presented, mainly based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain). All the available units of the selected model of photomultiplier have been screened together with most of the components for the bases, enclosures and windows. According to these results for the activity of the relevant radioisotopes, the selected components of the energy plane would give a contribution to the overall background level in the region of interest of at most 2.4 × 10¿4 counts per keV, kg and year, satisfying the sensitivity requirements of the NEXT experiment., Special thanks are due to LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. We are really grateful to Grzegorz Zuzel for the radon emanation measurements. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04 and the Severo Ochoa Program SEV-2014-0398; the GVA of Spain under grant PROMETEO/2016/120; the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS/103860/2008; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory) and DE-FG02-13ER42020 (Texas A & and the University of Texas at Arlington.

[EN] We introduce a simulation framework for the transport of high and low energy electrons in xenon-based optical time projection chambers (OTPCs). The simulation relies on elementary cross sections (electron-atom and electron-molecule) and incorporates, in order to compute the gas scintillation, the reaction/quenching rates (atom-atom and atom-molecule) of the first 41 excited states of xenon and the relevant associated excimers, together with their radiative cascade. The results compare positively with observations made in pure xenon and its mixtures with CO2 and CF4 in a range of pressures from 0.1 to 10 bar. This work sheds some light on the elementary processes responsible for the primary and secondary xenon-scintillation mechanisms in the presence of additives, that are of interest to the OTPC technology., DGD is supported by the Ramon y Cajal program (Spain) under contract number RYC-2015-18820. The authors want to acknowledge the RD51 collaboration for encouragement and support during the elaboration of this work, and in particular discussions with F. Resnati, A. Milov, V. Peskov, M. Suzuki and A. F. Borghesani. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04 and the Severo Ochoa Program SEV-2014-0398; the GVA of Spain under grant PROM-ETEO/2016/120; the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory) and DE-FG02-13ER42020 (Texas A& and the University of Texas at Arlington.

The NEXT experiment aims to observe the neutrinoless double beta decay of Xe-136 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 Qbb 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., Comment: Proceedings of the XXVII International Conference on Neutrino Physics and Astrophysics (Neutrino), London, July 2016

Liquid xenon has several attractive features, which make it suitable for applications to nuclear medicine, such as high scintillation yield and fast scintillation decay time, better than currently used crystals. Since the '90s, several attempts has been made to build Positron Emission Tomography scanners based on liquid xenon, which can be divided into two different approaches: on one hand, the detection of the ionization charge in TPCs, and, on the other one, the detection of scintillation light with photomultipliers. PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel concept, which combines liquid xenon scintillating cells and silicon photomultipliers for the readout. A first Monte Carlo investigation has pointed out that this technology would provide an excellent intrinsic time resolution, which makes it possible to measure the Time-Of-Flight with high efficiency. Also, the transparency of liquid xenon to UV and blue wavelengths opens the possibility of exploiting both scintillation and Cherenkov light for a high-sensitivity TOF-PET., Comment: Proceedings of the Lidine '17 conference. Accepted by JINST

In this paper we use detailed Monte Carlo simulations to demonstrate that liquid xenon (LXe) can be used to build a Cherenkov-based TOF-PET, with an intrinsic coincidence resolving time (CRT) in the vicinity of 10 ps. This extraordinary performance is due to three facts: a) the abundant emission of Cherenkov photons by liquid xenon; b) the fact that LXe is transparent to Cherenkov light; and c) the fact that the fastest photons in LXe have wavelengths higher than 300 nm, therefore making it possible to separate the detection of scintillation and Cherenkov light. The CRT in a Cherenkov LXe TOF-PET detector is, therefore, dominated by the resolution (time jitter) introduced by the photosensors and the electronics. However, we show that for sufficiently fast photosensors (e.g, an overall 40 ps jitter, which can be achieved by current micro-channel plate photomultipliers) the overall CRT varies between 30 and 55 ps, depending of the detection efficiency. This is still one order of magnitude better than commercial CRT devices and improves by a factor 3 the best CRT obtained with small laboratory prototypes., Comment: accepted by JINST

Gómez Cadenas, Juan José et al., 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 Subterráneo 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., This work was supported by the following agencies and institutions: the Ministerio de Economía y Competitividad 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 Neutrino Experiment with a Xenon Time-Projection Chamber (NEXT) is intended to investigate the neutrinoless double beta decay of 136Xe, which requires a severe suppression of potential backgrounds; therefore, an extensive screening and selection process is underway to control the radio-purity levels of the materials to be used in the experimental set-up of NEXT. The detector design combines the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. Separate energy and tracking readout planes are based on different sensors: photomultiplier tubes for calorimetry and silicon multi-pixel photon counters for tracking. The design of a radio pure tracking plane, in direct contact with the gas detector medium, was a challenge since the needed components have typically activities too large for experiments requiring ultra-low background conditions. Here, the radiopurity assessment of tracking readout components based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain) is described. According to the obtained results, radiopure enough printed circuit boards made of kapton and copper and silicon photomultipliers., We deeply acknowledge John Murphy and Carl Jackson from SensL Technologies Ltd for their efficient collaboration in the analysis of SiPMs. We very much thank also Vicenzo Mancini from SOMACIS company for the care in the development of radiopure kapton PCBs. Special thanks are due to LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. The NEXT Collaboration acknowledges funding support from the following agencies and institutions: the European Research Council under the Advanced Grant 339787-NEXT and the T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; the Spanish Ministerio de Economia y Competitividad 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 DoE 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.

[EN] A technical description of NEXT-MM and its commissioning and first performance is reported. Having an active volume of ∼35 cm drift × 28 cm diameter, it constitutes the largest Micromegas-read TPC operated in Xenon ever constructed, made by a sectorial arrangement of the 4 largest single wafers manufactured with the Microbulk technique to date. It is equipped with a suitably pixelized readout and with a sufficiently large sensitive volume (∼23 l) so as to contain long (∼20 cm) electron tracks. First results obtained at 1 bar for Xenon and Trymethylamine (Xe-(2%)TMA) mixture are presented. The TPC can accurately reconstruct extended background tracks. An encouraging full-width half-maximum of 11.6 % was obtained for ∼29 keV gammas without resorting to any data post-processing., The NEXT Collaboration acknowledges funding support from the following agencies and institutions: the Spanish Ministerio de Economia y Competitividad under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), Consolider-Ingenio 2010 CSD2007- 00042 (CPAN), and under contracts ref. FPA2008-03456, FPA2009-13697-C04-04; FCT(Lisbon) and FEDER under grant PTDC/FIS/103860/2008; the European Commission under the European Research Council T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. Part of these grants are funded by the European Regional Development Fund (ERDF/FEDER). J. Renner (LBNL) acknowledges the support of a US DOE NNSA Stewardship Science Graduate Fellowship under contract no. DE-FC52-08NA28752. F.I. acknowledges the support from the Eurotalents program. We are also grateful to our colleagues of the RD-51 collaboration for helpful discussions and encouragement. Finally, authors would like to acknowledge the use of Servicio General de Apoyo a la Investigacion-SAI of the Universidad de Zaragoza and R. de Oliveira and his team at CERN for the manufacturing of the Micromegas readouts.

NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double-beta (\beta \beta 0\nu) decay experiment that will operate at the Canfranc Underground Laboratory (LSC). It is an electroluminescent high-pressure gaseous xenon Time Projection Chamber (TPC) with separate read-out planes 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 (, Comment: 3 pages, 3 figures, 2 tables. Proceedings from the poster session at the 37th International Conference on High Energy Physics (ICHEP, Valencia, Jul 2014)

The measurement of the time of flight of the two 511 keV gammas recorded in coincidence in a PET scanner provides an effective way of reducing the random background and therefore increases the scanner sensitivity, provided that the coincidence resolving time (CRT) of the gammas is sufficiently good. The best commercial PET-TOF system today (based in LYSO crystals and digital SiPMs), is the VEREOS of Philips, boasting a CRT of 316 ps (FWHM). In this paper we present a Monte Carlo investigation of the CRT performance of a PET scanner exploiting the scintillating properties of liquid xenon. We find that an excellent CRT of 70 ps (depending on the PDE of the sensor) can be obtained if the scanner is instrumented with silicon photomultipliers (SiPMs) sensitive to the ultraviolet light emitted by xenon. Alternatively, a CRT of 160 ps can be obtained instrumenting the scanner with (much cheaper) blue-sensitive SiPMs coated with a suitable wavelength shifter. These results show the excellent time of flight capabilities of a PET device based in liquid xenon., Accepted by JINST

[EN] Silicon photomultipliers (SiPM) are the photon detectors chosen for the tracking readout in NEXT, a neutrinoless \bb decay experiment which uses a high pressure gaseous xenon time projection chamber (TPC). The reconstruction of event track and topology in this gaseous detector is a key handle for background rejection. Among the commercially available sensors that can be used for tracking, SiPMs offer important advantages, mainly high gain, ruggedness, cost-effectiveness and radio-purity. Their main drawback, however, is their non sensitivity in the emission spectrum of the xenon scintillation (peak at 175 nm). This is overcome by coating these sensors with the organic wavelength shifter tetraphenyl butadiene (TPB). In this paper we describe the protocol developed for coating the SiPMs with TPB and the measurements performed for characterizing the coatings as well as the performance of the coated sensors in the UV-VUV range. © 2012 IOP Publishing Ltd and SISSA., We acknowledge the Spanish MICINN for the Consolider Ingenio grants under contracts CSD2008-00037, CSD2007-00042 and CSD2007-00010 and for the research grants under contract FPA2008-03456 and FPA2009-13697-C04-01 part of which come from FEDER funds. The Portuguese team acknowledges support from FCT and FEDER through program COMPETE, project PTDC/FIS/103860/2008. J. Renner acknowledges the support of the U.S. Department of Energy Stewardship Science Graduate Fellowship, grant number DE-FC52-08NA28752.

[EN] The "Neutrino Experiment with a Xenon Time-Projection Chamber" (NEXT) is intended to investigate the neutrinoless double beta decay of Xe-136, which requires a severe suppression of potential backgrounds. An extensive screening and material selection process is underway for NEXT since the control of the radiopurity levels of the materials to be used in the experimental set-up is a must for rare event searches. First measurements based on Glow Discharge Mass Spectrometry and gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterraneo de Canfranc (Spain) are described here. Activity results for natural radioactive chains and other common radionuclides are summarized, being the values obtained for some materials like copper and stainless steel very competitive. The implications of these results for the NEXT experiment are also discussed., We deeply acknowledge LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. The NEXT Collaboration acknowledges funding support from the following agencies and institutions: the Spanish Ministerio de Economia y Competitividad under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), Consolider-Ingenio 2010 CSD2007-00042 (CPAN), and under contracts ref. FPA2008-03456, FPA2009-13697-C04-04; FCT(Lisbon) and FEDER under grant PTDC/FIS/103860/2008; the European Commission under the European Research Council T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. Part of these grants are funded by the European Regional Development Fund (ERDF/FEDER). J. Renner (LBNL) acknowledges the support of a US DOE NNSA Stewardship Science Graduate Fellowship under contract no. DE-FC52-08NA28752. F.I. acknowledges the support from the Eurotalents program.

El Pdf del artículo es la versión pre-print: arXiv:1010.5112v4, The search for neutrinoless double beta decay is a very active field in which the number of proposals for next-generation experiments has proliferated. In this paper we attempt to address both the sense and the sensitivity of such proposals. Sensitivity comes first, by means of proposing a simple and unambiguous statistical recipe to derive the sensitivity to a putative Majorana neutrino mass, mββ. In order to make sense of how the different experimental approaches compare, we apply this recipe to a selection of proposals, comparing the resulting sensitivities. We also propose a ``physics-motivated range'' (PMR) of the nuclear matrix elements as a unifying criterium between the different nuclear models. The expected performance of the proposals is parametrized in terms of only four numbers: energy resolution, background rate (per unit time, isotope mass and energy), detection efficiency, and ββ isotope mass. For each proposal, both a reference and an optimistic scenario for the experimental performance are studied. In the reference scenario we find that all the proposals will be able to partially explore the degenerate spectrum, without fully covering it, although four of them (KamLAND-Zen, CUORE, NEXT and EXO) will approach the 50 meV boundary. In the optimistic scenario, we find that CUORE and the xenon-based proposals (KamLAND-Zen, EXO and NEXT) will explore a significant fraction of the inverse hierarchy, with NEXT covering it almost fully. For the long term future, we argue that 136Xe-based experiments may provide the best case for a 1-ton scale experiment, given the potentially very low backgrounds achievable and the expected scalability to large isotope masses., The authors acknowledge support by the Spanish Ministry of Science and Innovation (MICINN) under grants CONSOLIDER-INGENIO 2010 CSD2008-0037 (CUP), FPA2009-13697-C04-04 and RYC-2008-03169.

The LHC is a promising machine to discover new physics in the top sector. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. The production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. At the Tevatron, a 2 sigma discrepancy with the SM prediction for the forward--backward asymmetry has been found, boosting a renewed interest for this kind of models. We consider a toy model with general flavour dependent couplings of the resonance to quarks, of both vector and axial-vector kind and investigate the possible constraints on the coupling space from the measurement of the asymmetry and the invariant mass distribution at the Tevatron. Then, we define a central asymmetry in a specific kinematic region and investigate its signature at the LHC as well as its statistical significance, for exclusive processes., Proceedings of XVIII International Workshop on Deep-Inelastic Scattering and Related Subjects, April 19 -23, 2010, Firenze

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2 sigma. In this letter, we explore the possibility of reconciling the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks., We thank the CERN TH TOP09 Institute, where this work was initiated, for hospitality and for many useful discussions. The work of P.F. is supported by the Consejo Superior de Investigaciones Cient´ıficas (CSIC). This work is also supported by the Ministerio de Ciencia e Innovación under Grant No. FPA2007-60323, by CPAN(Grant No. CSD2007-00042), by the Generalitat Valenciana under Grant No.PROMETEO/2008/069, and by the European Commission MRTN FLAVIAnet under Contract No. MRTN-CT-2006-035482.

With the next start of LHC, a huge production of top quarks is expected. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. A peak in the differential cross section could reveal the existence of such a resonance, but this is experimentally challenging, because it requires selecting data samples where top and antitop quarks are highly boosted. Nonetheless, the production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. We consider a toy model with general flavour independent couplings of the resonance to quarks, of both vector and axial-vector kind. The charge asymmetry turns out to be a more powerful observable to detect new physics than the differential cross section, because its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses.

Several models predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range that might be discovered at the LHC. In some of those models, moreover, a sizable charge asymmetry of top versus antitop quarks might be generated. The detection of these exotic resonances, however, requires selecting data samples where the top and the antitop quarks are highly boosted, which is experimentally very challenging. We asses that the measurement of the top quark charge asymmetry at the LHC is very sensitive to the existence of excited states of the gluon with axial-vector couplings to quarks. We use a toy model with general flavour independent couplings, and show that a signal can be detected with relatively not too energetic top and antitop quarks. We also compare the results with the asymmetry predicted by QCD, and show that its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses., 20 pages

Combining the Berends-Giele and on-shell recursion relations we obtain an extremely compact expression for the scattering amplitude of a complex scalar-antiscalar pair and an arbitrary number of positive helicity gluons. This is one of the basic building blocks for constructing other helicity configurations from recursion relations. We also show explicity that the all positive helicity gluons amplitude for heavy fermions is proportional to the scalar one, confirming in this way the recently advocated SUSY-like Ward identities relating both amplitudes., 7 pages

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 gamma-ray spectrometry performed at the Canfranc Underground Laboratory; recent results of this material screening program are presented here., Proceedings for a poster contribution at ICHEP 2014, Valencia, Spain

Ionization and scintillation produced by nuclear recoils in gaseous xenon at approximately 14 bar have been simultaneously observed in an electroluminescent time projection chamber. Neutrons from radioisotope α-Be neutron sources were used to induce xenon nuclear recoils, and the observed recoil spectra were compared to a detailed Monte Carlo employing estimated ionization and scintillation yields for nuclear recoils. The ability to discriminate between electronic and nuclear recoils using the ratio of ionization to primary scintillation is demonstrated. These results encourage further investigation on the use of xenon in the gas phase as a detector medium in dark matter direct detection experiments., This work was supported by the following agencies and institutions: the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, and the National Energy Research Scientific Computing Center (NERSC), supported by the Office of Science of the U.S. Department of Energy, both under Contract no. DE-AC02-05CH11231; the European Research Council under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under Grants CONSOLIDER-Ingenio 2010 C5D2008-0037 (CUP), FPA2009-13697-004-04, FPA2009-13697-C04-01, FIS2012-37947-C04-01, FIS2012-37947-C04-02, FIS2012-37947-C04-03, and FIS2012-37947-C04-04; and the Portuguese FCT and FEDER through the program COMPETE, Projects PTDC/FIS/103860/2008 and PTDC/FIS/112272/2009. J. Renner acknowledges the support of a Department of Energy National Nuclear Security Administration Stewardship Science Graduate Fellowship, grant number DE-FC52-08NA28752.

[EN] A new method to tag the barium daughter in the double-beta decay of Xe-136 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 (similar to 2 nm), and detected with a statistical significance of 12.9 sigma 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., NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under Advanced Grant No. 339787-NEXT, the Ministerio de Economia y Competitividad of Spain under Grants No. FIS2014-53371-C04 and the Severo Ochoa Program SEV-2014-0398, the Generalitat Valenciana (GVA) of Spain under Grant No. PROMETEO/2016/120, the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS/103860/2008, the U.S. Department of Energy under Contracts No. DE-AC02-07CH11359 (Fermi National Accelerator Laboratory) and No. DE-FG02-13ER42020 (Texas A&M) and No. DE-SC0017721 (University of Texas at Arlington), and the University of Texas at Arlington.