NEXT-100 is currently being constructed at the Laboratorio Subterráneo de Canfranc in the Spanish Pyrenees and will search for neutrinoless double beta decay using a high-pressure gaseous time ...projection chamber (TPC) with 100 kg of xenon. Charge amplification is carried out via electroluminescence (EL) which is the process of accelerating electrons in a high electric field region causing secondary scintillation of the medium proportional to the initial charge. The NEXT-100 EL and cathode regions are made from tensioned hexagonal meshes of 1 m diameter. This paper describes the design, characterization, and installation of these parts for NEXT-100. Simulations of the electric field are performed to model the drift and amplification of ionization electrons produced in the detector under various EL region alignments and rotations. Measurements of the electrostatic breakdown voltage in air characterize performance under high voltage conditions and identify breakdown points. The electrostatic deflection of the mesh is quantified and fit to a first-principles mechanical model. Measurements were performed with both a standalone test EL region and with the NEXT-100 EL region before its installation in the detector. Finally, we describe the parts as installed in NEXT-100, following their deployment in Summer 2023.
The NEXT experiment aims at the sensitive search of the neutrinoless double beta decay in \(^{136}\)Xe, 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 neutrinoless double beta decay search. The analysis considers the combination of 271.6 days of \(^{136}\)Xe-enriched data and 208.9 days of \(^{136}\)Xe-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\(\pm\)0.01 kg of \(^{136}\)Xe-enriched xenon, 90% C.L. lower limits to the neutrinoless double beta decay are found in the T\(_{1/2}^{0\nu}>5.5\times10^{23}-1.3\times10^{24}\) 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.
The search for neutrinoless double beta decay (\(0\nu\beta\beta\)) remains one of the most compelling experimental avenues for the discovery in the neutrino sector. Electroluminescent gas-phase time ...projection chambers are well suited to \(0\nu\beta\beta\) searches due to their intrinsically precise energy resolution and topological event identification capabilities. Scalability to ton- and multi-ton masses requires readout of large-area electroluminescent regions with fine spatial resolution, low radiogenic backgrounds, and a scalable data acquisition system. This paper presents a detector prototype that records event topology in an electroluminescent xenon gas TPC via VUV image-intensified cameras. This enables an extendable readout of large tracking planes with commercial devices that reside almost entirely outside of the active medium.Following further development in intermediate scale demonstrators, this technique may represent a novel and enlargeable method for topological event imaging in \(0\nu\beta\beta\).
The experimental study of the reduced mobility K 0 of the molecular ions H 3 + /H 5 + in H 2 and D 3 + /D 5 + in D 2 was carried out using a recently developed technique, that uses a Xe VUV flash ...lamp and a Gaseous Electron Multiplier (GEM) microstructure with a CsI deposit to produce the molecular ions by electron avalanche ionization. For both gases, the K 0 values were obtained at room temperature (295 K) and at pressures from 5 to 50 Torr for uniform reduced electric fields E/N from 4 to 40 Td. The reduced mobility derived from the measurements is an average of the K 0 value of the two molecular ions, and for the H 3 + and H 5 + ions is 11.1 cm 2 V -1 s -1 while for D 3 + and D 5 + it ranges from 8.5 to 7.8 cm 2 V -1 s -1 , for pressure from 5 to 50 Torr. A discussion of the obtained results is presented.
We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single ...or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cobalt samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean \(\mathrm{Ba^{2+}}\) ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb\(^{2+}\) and Cd\(^{2+}\) also demonstrated for this purpose.
Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. In noble element systems, it is often coated with ...tetraphenyl butadiene (TPB) to allow detection of vacuum ultraviolet scintillation light. In this work this dependence is investigated for PTFE coated with TPB in air for light of wavelengths of 200~nm, 260~nm, and 450~nm. The results show that TPB-coated PTFE has a reflectance of approximately 92\% for thicknesses ranging from 5~mm to 10~mm at 450~nm, with negligible variation as a function of thickness within this range. A cross-check of these results using an argon chamber supports the conclusion that the change in thickness from 5~mm to 10~mm does not affect significantly the light response at 128~nm. Our results indicate that pieces of TPB-coated PTFE thinner than the typical 10~mm can be used in particle physics detectors without compromising the light signal.
We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White TPC and a dedicated setup. Detailed comparison with first-principle calculations ...allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that has been postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10\(^{-2}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at pressure-reduced electric field values of 50 V cm\(^{-1}\) bar\(^{-1}\) to above 3\(\times\)10\(^{-1}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at 500 V cm\(^{-1}\) bar\(^{-1}\). Above 1.5 kV cm\(^{-1}\) bar\(^{-1}\), values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\), which is about two orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the "buffer" and "veto" regions, where keeping the electric field below the electroluminescence (EL) threshold will not suffice to extinguish secondary scintillation. The electric field in these regions should be chosen carefully to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path towards obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e\(^{-}\) cm\(^{-1}\).
We report a measurement of the half-life of the \({}^{136}\)Xe two-neutrino double beta decay performed with a novel direct background subtraction technique. The analysis relies on the data collected ...with the NEXT-White detector operated with \({}^{136}\)Xe-enriched and \({}^{136}\)Xe-depleted xenon, as well as on the topology of double-electron tracks. With a fiducial mass of only 3.5 kg of Xe, a half-life of \(2.34^{+0.80}_{-0.46}\textrm{(stat)}^{+0.30}_{-0.17}\textrm{(sys)}\times10^{21}~\textrm{yr}\) is derived from the background-subtracted energy spectrum. The presented technique demonstrates the feasibility of unique background-model-independent neutrinoless double beta decay searches.
If neutrinos are their own antiparticles, the otherwise-forbidden nuclear reaction known as neutrinoless double beta decay (\(\beta\beta 0\nu\)) can occur, with a characteristic lifetime which is ...expected to be very long, making the suppression of backgrounds a daunting task. It has been shown that detecting (``tagging'') the Ba\(^{+2}\) dication produced in the double beta decay \({}^{136}\mathrm{Xe} \rightarrow {}^{136}\)Ba\(^{+2}+ 2 e + (2 \nu)\) in a high pressure gas experiment, could lead to a virtually background free experiment. To identify these \Bapp, chemical sensors are being explored as a key tool by the NEXT collaboration . Although used in many fields, the application of such chemosensors to the field of particle physics is totally novel and requires experimental demonstration of their suitability in the ultra-dry environment of a xenon gas chamber. Here we use a combination of complementary surface science techniques to unambiguously show that Ba\(^{+2}\) ions can be trapped (chelated) in vacuum by an organic molecule, the so-called fluorescent bicolour indicator (FBI) (one of the chemosensors developed by NEXT), immobilized on a surface. We unravel the ion capture mechanism once the molecules are immobilised on Au(111) surface and explain the origin of the emission fluorescence shift associated to the trapping of different ions. Moreover, we prove that chelation also takes place on a technologically relevant substrate, as such, demonstrating the feasibility of using FBI indicators as building blocks of a Ba\(^{+2}\) detector.
Radio-frequency (RF) carpets with ultra-fine pitches are examined for ion transport in gases at atmospheric pressures and above. We develop new analytic and computational methods for modeling RF ion ...transport at densities where dynamics are strongly influenced by buffer gas collisions. An analytic description of levitating and sweeping forces from phased arrays is obtained, then thermodynamic and kinetic principles are used to calculate ion loss rates in the presence of collisions. This methodology is validated against detailed microscopic SIMION simulations. We then explore a parameter space of special interest for neutrinoless double beta decay experiments: transport of barium ions in xenon at pressures from 1 to 10 bar. Our computations account for molecular ion formation and pressure dependent mobility as well as finite temperature effects. We discuss the challenges associated with achieving suitable operating conditions, which lie beyond the capabilities of existing devices, using presently available or near-future manufacturing techniques.
