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Gomez-Cadenas, J. J., Martin-Albo, J., Mezzetto, M., Monrabal, F., & Sorel, M. (2012). The search for neutrinoless double beta decay. Riv. Nuovo Cimento, 35(2), 29–98.
Abstract: In the last two decades the search for neutrinoless double beta decay has evolved into one of the highest priorities for understanding neutrinos and the origin of mass. The main reason for this paradigm shift has been the discovery of neutrino oscillations, which clearly established the existence of massive neutrinos. An additional motivation for conducting such searches comes from the existence of an unconfirmed, but not refuted, claim of evidence for neutrinoless double decay in Ge-76. As a consequence, a new generation of experiments, employing different detection techniques and beta beta isotopes, is being actively promoted by experimental groups across the world. In addition, nuclear theorists are making remarkable progress in the calculation of the neutrinoless double beta. decay nuclear matrix elements, thus eliminating a substantial part of the theoretical uncertainties affecting the particle physics interpretation of this process. In this report, we review the main aspects of the double beta decay process and some of the most relevant experiments. The picture that emerges is one where searching for neutrinoless double beta decay is recognized to have both far-reaching theoretical implications and promising prospects for experimental observation in the near future.
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Gomez-Cadenas, J. J., Martin-Albo, J., Menendez, J., Mezzetto, M., Monrabal, F., & Sorel, M. (2024). The search for neutrinoless double-beta decay. Riv. Nuovo Cimento, 46, 619–692.
Abstract: Neutrinos are the only particles in the Standard Model that could be Majorana fermions, that is, completely neutral fermions that are their own antiparticles. The most sensitive known experimental method to verify whether neutrinos are Majorana particles is the search for neutrinoless double-beta decay. The last 2 decades have witnessed the development of a vigorous program of neutrinoless double-beta decay experiments, spanning several isotopes and developing different strategies to handle the backgrounds masking a possible signal. In addition, remarkable progress has been made in the understanding of the nuclear matrix elements of neutrinoless double-beta decay, thus reducing a substantial part of the theoretical uncertainties affecting the particle-physics interpretation of the process. On the other hand, the negative results by several experiments, combined with the hints that the neutrino mass ordering could be normal, may imply very long lifetimes for the neutrinoless double-beta decay process. In this report, we review the main aspects of such process, the recent progress on theoretical ideas and the experimental state of the art. We then consider the experimental challenges to be addressed to increase the sensitivity to detect the process in the likely case that lifetimes are much longer than currently explored, and discuss a selection of the most promising experimental efforts.
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NEMO-3 Collaboration(Argyriades, J. et al), Martin-Albo, J., & Novella, P. (2010). Measurement of the two neutrino double beta decay half-life of Zr-96 with the NEMO-3 detector. Nucl. Phys. A, 847(3-4), 168–179.
Abstract: Using 9.4 g of Zr-96 isotope and 1221 days of data from the NEMO-3 detector corresponding (0 0.031 kg y, the obtained 2 nu beta beta decay half-life measurement is T-1/2(2 nu) = [2.35 +/- 0.14(stat) +/- 0.16(syst)] x 10(19) yr. Different characteristics of the final state electrons have been studied, such as the energy sum, individual electron energy, and angular distribution. The 2v nuclear matrix element is extracted using the measured 2 nu beta beta half-life and is M-2 nu = 0.049 +/- 0.002. Constraints on 0 nu beta beta decay have also been set.
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NEXT Collaboration(Henriques, C. A. O. et al), Gomez-Cadenas, J. J., Alvarez, V., Benlloch-Rodriguez, J., Botas, A., Carcel, S., et al. (2017). Secondary scintillation yield of xenon with sub-percent levels of CO2 additive for rare-event detection. Phys. Lett. B, 773, 663–671.
Abstract: Xe-CO2 mixtures are important alternatives to pure xenon in Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification with applications in the important field of rare event detection such as directional dark matter, double electron capture and double beta decay detection. The addition of CO2 to pure xenon at the level of 0.05-0.1% can reduce significantly the scale of electron diffusion from 10 mm/root m to 2.5 mm/root m, with high impact on the discrimination of the events through pattern recognition of the topology of primary ionization trails. We have measured the electroluminescence (EL) yield of Xe-CO2 mixtures, with sub-percent CO2 concentrations. We demonstrate that the EL production is still high in these mixtures, 70% and 35% relative to that produced in pure xenon, for CO2 concentrations around 0.05% and 0.1%, respectively. The contribution of the statistical fluctuations in EL production to the energy resolution increases with increasing CO2 concentration, being smaller than the contribution of the Fano factor for concentrations below 0.1% CO2.
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Cervera-Villanueva, A., Laing, A., Martin-Albo, J., & Soler, F. J. P. (2010). Performance of the MIND detector at a Neutrino Factory using realistic muon reconstruction. Nucl. Instrum. Methods Phys. Res. A, 624(3), 601–614.
Abstract: A Neutrino Factory producing an intense beam composed of v(e)((v) over bar (e)) and (v) over bar (mu)(v(mu)) from muon decays has been shown to have the greatest sensitivity to the two currently unmeasured neutrino mixing parameters theta(13) and delta(CP) Using the wrong-sign muon signal to measure v(e)-> v(mu)((v) over bar (e) ->(v) over bar (mu)) oscillations in a 50kt Magnetised Iron Neutrino Detector (MIND) sensitivity to delta(CP) could be maintained down to small values of theta(13) However the detector efficiencies used in these previous studies were calculated assuming perfect pattern recognition In this paper MIND is reassessed taking into account for the first time a realistic pattern recognition for the muon candidate Reoptimisation of the analysis utilises a combination of methods including a multivariate analysis similar to the one used in MINOS to maintain high efficiency while suppressing backgrounds ensuring that the signal selection efficiency and the background levels are comparable or better than the ones in previous analyses As a result MIND remains the most sensitive future facility for the discovery of CP violation from neutrino oscillations.
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NEMO-3 Collaboration(Argyriades, J. et al), Diaz, J., Martin-Albo, J., Monrabal, F., Novella, P., Serra, L., et al. (2011). Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors. Nucl. Instrum. Methods Phys. Res. A, 625(1), 20–28.
Abstract: We have constructed a GEANT4-based detailed software model of photon transport in plastic sontillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutnnoless double beta decay We compare our simulations to measurements using conversion electrons from a calibration source of (BI)-B-207 and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account In this article we briefly describe our modeling approach and results of our studies.
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NEXT Collaboration(Alvarez, V. et al), Carcel, S., Cervera-Villanueva, A., Diaz, J., Ferrario, P., Gil, A., et al. (2013). Near-intrinsic energy resolution for 30-662 keV gamma rays in a high pressure xenon electroluminescent TPC. Nucl. Instrum. Methods Phys. Res. A, 708, 101–114.
Abstract: We present the design, data and results from the NEXT prototype for Double Beta and Dark Matter (NEXT-DBDM) detector, a high-pressure gaseous natural xenon electroluminescent time projection chamber (TPC) that was built at the Lawrence Berkeley National Laboratory. It is a prototype of the planned NEXT-100 Xe-136 neutrino-less double beta decay (0 nu beta beta) experiment with the main objectives of demonstrating near-intrinsic energy resolution at energies up to 662 keV and of optimizing the NEXT-100 detector design and operating parameters. Energy resolutions of similar to 1% FWHM for 662 keV gamma rays were obtained at 10 and 15 atm and similar to 5% FWHM for 30 keV fluorescence xenon X-rays. These results demonstrate that 0.5% FWHM resolutions for the 2459 keV hypothetical neutrino-less double beta decay peak are realizable. This energy resolution is a factor 7-20 better than that of the current leading 0 nu beta beta experiments using liquid xenon and thus represents a significant advancement. We present also first results from a track imaging system consisting of 64 silicon photo-multipliers recently installed in NEXT-DBDM that, along with the excellent energy resolution, demonstrates the key functionalities required for the NEXT-100 0 nu beta beta search.
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NEXT Collaboration(Renner, J. et al), Alvarez, V., Carcel, S., Cervera-Villanueva, A., Diaz, J., Ferrario, P., et al. (2015). Ionization and scintillation of nuclear recoils in gaseous xenon. Nucl. Instrum. Methods Phys. Res. A, 793, 62–74.
Abstract: 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 a-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.
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NEXT Collaboration(Cebrian, S. et al), Alvarez, V., Carcel, S., Cervera-Villanueva, A., Diaz, J., Ferrario, P., et al. (2015). Accurate gamma and MeV-electron track reconstruction with an ultra-low diffusion Xenon/TMA TPC at 10 atm. Nucl. Instrum. Methods Phys. Res. A, 804, 8–24.
Abstract: We report the performance of a 10 atm Xenon/trimethylamine time projection chamber (TPC) for the detection of X-rays (30 keV) and gamma-rays (0.511-1.275 MeV) in conjunction with the accurate tracking of the associated electrons. When operated at such a high pressure and in similar to 1%-admixtures, trimethylamine (TMA) endows Xenon with an extremely low electron diffusion (1.3 +/- 0.13 mm-sigma (longitudinal), 0.95 +/- 0.20 mm-sigma (transverse) along 1 m drift) besides forming a convenient Penning-Fluorescent' mixture. The TPC, that houses 1.1 kg of gas in its fiducial volume, operated continuously for 100 live-days in charge amplification mode. The readout was performed through the recently introduced microbulk Micromegas technology and the AFTER chip, providing a 3D voxelization of 8 mm x 8 mm x 1.2 mm for approximately 10 cm/MeV-long electron tracks. Resolution in energy (epsilon) at full width half maximum (R) inside the fiducial volume ranged from R = 14.6% (30 keV) to R = 4.6% (1.275 MeV). This work was developed as part of the R&D program of the NEXT collaboration for future detector upgrades in the search of the neutrino-less double beta decay (beta beta 0 nu) in Xe-136, specifically those based on novel gas mixtures. Therefore we ultimately focus on the calorimetric and topological properties of the reconstructed MeV-electron tracks. In particular, the obtained energy resolution has been decomposed in its various contributions and improvements towards achieving the R =1.4%root MeV/epsilon levels obtained in small sensors are discussed.
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NEXT Collaboration(Azevedo, C. D. R. et al), Gomez-Cadenas, J. J., Alvarez, V., Benlloch-Rodriguez, J. M., Botas, A., Carcel, S., et al. (2018). Microscopic simulation of xenon-based optical TPCs in the presence of molecular additives. Nucl. Instrum. Methods Phys. Res. A, 877, 157–172.
Abstract: 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.
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