Search

We investigate contributions to the anomalous magnetic moments of charged leptons in the neutrino-extended Standard Model Effective Field Theory ($\nu$SMEFT). We discuss how $\nu$SMEFT operators can contribute to a lepton's magnetic moment at one- and two-loop order. We show that only one operator can account for existing electronic and muonic discrepancies, assuming new physics appears above $1$ TeV. In particular, we find that a right-handed charged current in combination with minimal sterile-active mixing can explain the discrepancy for sterile neutrino masses of $\mathcal O(100)$ GeV while avoiding direct and indirect constraints. We discuss how searches for sterile neutrino production at the (HL-)LHC, measurements of $h\rightarrow \mu^+ \mu^-$ and searches for $h\rightarrow e^+ e^-$, neutrinoless double beta decay experiments, and improved unitarity tests of the CKM matrix can further probe the relevant parameter space., Comment: Journal version. 37 pages (incl. references), 6 figures, 4 tables. vSMEFT FeynRules UFO available from https://feynrules.irmp.ucl.ac.be/wiki/HeavyN

The NEXT collaboration: et al., The Neutrino Experiment with a Xenon TPC (NEXT) searches for the neutrinoless double-beta (0νββ) decay of 136Xe using high-pressure xenon gas TPCs with electroluminescent amplification. A scaled-up version of this technology with about 1 tonne of enriched xenon could reach in less than 5 years of operation a sensitivity to the half-life of 0νββ decay better than 1027 years, improving the current limits by at least one order of magnitude. This prediction is based on a well-understood background model dominated by radiogenic sources. The detector concept presented here represents a first step on a compelling path towards sensitivity to the parameter space defined by the inverted ordering of neutrino masses, and beyond., 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 Economía y Competitividad and the Ministerio de Ciencia, Innovación 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 María de Maeztu Program MDM2016-0692; the Generalitat Valenciana 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 Pazy Foundation (Israel) under grants 877040 and 877041; the US 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 support from the Ramón y Cajal program (Spain) under contract number RYC-2015-18820. JM-A acknowledges support from Fundación Bancaria la Caixa (ID 100010434), grant code LCF/BQ/PI19/11690012, and from the Plan GenT program of the Generalitat Valenciana, grant code CIDEGENT/2019/049.

Particle tracks and differential energy loss measured in high pressure gaseous detectors can be exploited for event identification in neutrinoless double beta decay (0νββ) searches. We develop a new method based on Kalman Filter in a Bayesian formalism (KFB) to reconstruct meandering tracks of MeV-scale electrons. With simulation data, we compare the signal and background discrimination power of the KFB method assuming different detector granularities and energy resolutions. Typical background from 232Th and 238U decay chains can be suppressed by another order of magnitude than that in published literatures, approaching the background-free regime. For the proposed PandaX-III experiment, the 0νββ search half-life sensitivity at the 90% confidence level would reach 2.7× 1026 yr with 5-year live time, a factor of 2.7 improvement over the initial design target.

Leptonic CP violating phase δ CP in the light neutrino sector and leptogenesis via present matter-antimatter asymmetry of the Universe entails each other. Probing CP violation in light neutrino oscillation is one of the challenging tasks today. The reactor mixing angle θ 13 measured in reactor experiments, LBL, and DUNE with high precision in neutrino experiments indicates towards the vast dimensions of scope to detect δ CP . The correlation between leptonic Dirac CPV phase δ CP , reactor mixing angle θ 13 , lightest neutrino mass m 1 , and matter-antimatter asymmetry of the Universe within the framework of μ − τ symmetry breaking assuming the type I seesaw dominance is extensively studied here. Here, a SO(10) GUT model with flavor μ − τ symmetry is considered. In this work, the idea is to link baryogenesis through leptogenesis and the hint of CP violation in the neutrino oscillation data to a breaking of the mu-tau symmetry. Small tiny breaking of the μ − τ symmetry allows a large Dirac CP violating phase in neutrino oscillation which in turn is characterized by awareness of measured value of θ 13 and to provide a hint towards a better understanding of the experimentally observed near-maximal value of ν μ − ν τ mixing angle θ 23 ≃ π / 4 . Precise breaking of the μ − τ symmetry is achieved by adding a 120-plet Higgs to the 10 + 1 2 ¯ 6 -dimensional representation of Higgs. The estimated three-dimensional density parameter space of the lightest neutrino mass m 1 , δ CP , and reactor mixing angle θ 13 is constrained here for the requirement of producing the observed value of baryon asymmetry of the Universe through the mechanism of leptogenesis. Carrying out numerical analysis, the allowed parameter space of m 1 , δ CP , and θ 13 is found out which can produce the observed baryon to photon density ratio of the Universe.

[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.

We study the connection between absolute neutrino mass and neutrino mixing parameters within $SO(10)$-inspired leptogenesis. We show that current favoured values of the unknown neutrino mixing parameters point toward values of the absolute neutrino mass scale that will be fully tested by cosmological observations and neutrinoless double beta decay experiments during next years. In particular, for $m_{D2}/m_{\rm charm} \leq 5$, where $m_{D2}$ is the intermediate Dirac neutrino mass, and for current best fit values of the Dirac phase $\delta$ and the atmospheric neutrino mixing angle $\theta_{23}$, we derive a lower bound on the neutrinoless double beta decay effective neutrino mass $m_{ee} \gtrsim 31\,{\rm meV}$ and on the sum of the neutrino masses $\sum_i m_i \gtrsim 125\,{\rm meV}$. These lower bounds hold for normally ordered neutrino masses, as currently favoured by global analyses and approximately for $\delta \in [155^\circ,240^\circ]$ and $\theta_{23}$ in the second octant. If values in this region will be confirmed by future planned long baseline experiments, then a signal at next generation neutrinoless double beta decay experiments is expected, despite neutrino masses being normally ordered. Outside the region, the lower bounds strongly relax but a great fraction of the allowed range of values still allows a measurement of the lightest neutrino mass. Therefore, in the the next years low energy neutrino experiments will provide a very stringent test of $SO(10)$-inspired leptogenesis, resulting either in severe constraints or in a strong evidence., Comment: 35 pages, 6 figures; v2: matching version submitted and to be published in JHEP

We have developed a dedicated front-end-electronics board for a high-pressure xenon gas time projection chamber for a neutrinoless double-beta decay search. The ionization signal is readout by detecting electroluminescence photons with SiPM's. The board readout the signal from 56~SiPM's through the DC-coupling and record the waveforms at 5 MS/s with a wide dynamic range up to 7,000 photons/200 ns. The SiPM bias voltages are provided by the board and can be adjusted for each SiPM. In order to calibrate and monitor the SiPM gain, additional auxiliary ADC measures 1 photon-equivalent dark current. The obtained performance satisfies the requirement for a neutrinoless double-beta decay search., 10 pages, 14 figures, This is a submitted version of conference record of IEEE NSS/MIC 2019

124Sn is one of the potential candidate isotopes for the study of $2\nu \beta \beta $ and $0\nu \beta \beta $ decay having a $\text{Q}_{ \boldsymbol {\beta \beta } }$ value of 2.228 MeV and natural isotopic abundance of 5.8%. 124Sn-loaded-liquid scintillator has been investigated for $2\nu \beta \beta $ and $0\nu \beta \beta $ decay search. Since $2\nu \beta \beta $ has not been experimentally observed from 124Sn isotope, unlike some of the isotopes subject to double-beta decay (DBD), it is necessary to study this element. However, lower light yield, chemical instability, and lower Sn-loading capability are some of the limitations of the liquid and plastic scintillators. The current investigation has been carried out to develop a single crystal of tetraphenyltin (TPSn) for the $2\nu \beta \beta $ and $0\nu \beta \beta $ decay search experiments. The TPSn powder for crystal growing was purified by recrystallization. The single crystals were grown using two-zone vertical Bridgman and slow solvent-evaporation techniques. Purified powder, diphenyloxazole (PPO), 1, 4-bis(2-methylstyryl) benzene (bis-MSB), and anthracene-doped Bridgman-grown crystal and anthracene-doped solvent-evaporation grown crystals showed X-ray induced emission peaking at 475 nm. The anthracene-doped crystal grown by solvent evaporation method showed scintillation under $\alpha $ -particles excitation from 241Am source. Two decay components, 16 ns with 68.7% and 132 ns with 31.3% relative contributions, were observed under $\alpha $ -particles excitation. This article suggests that after crystal growth optimization, TPSn can be a promising candidate for the DBD search of 124Sn.

We make a comparative study of the neutrinoless double beta decay constraints on heavy sterile neutrinos versus other direct and indirect constraints from both lepton number conserving and violating processes, as a sensitive probe of the extent of lepton number violation and possible interference effects in the sterile sector. We introduce a phenomenological parametrisation of the simplified one-generation seesaw model with one active and two sterile neutrino states in terms of experimentally measurable quantities, such as active-sterile neutrino mixing angles, CP phases, masses and mass splittings. This simple parametrisation enables us to analytically derive a spectrum of possible scenarios between the canonical seesaw with purely Majorana heavy neutrinos and inverse seesaw with pseudo-Dirac ones. We then go on to constrain the simplified parameters of this model from various experiments at the energy, intensity and cosmic frontiers. We emphasise that the constraints from lepton number violating processes strongly depend on the mass splitting between the two sterile states and the relative CP phase between them. This is particularly relevant for neutrinoless double beta decay, which is weakened for small mass splitting and opposite CP parities between the sterile states. On the other hand, neutrinoless double beta decay is especially sensitive for Majorana sterile neutrinos with masses around $0.1-10$ GeV., Comment: 55 pages, 13 figures

The past few decades have seen major developments in the design and operation of cryogenic particle detectors. This technology offers an extremely good energy resolution - comparable to semiconductor detectors - and a wide choice of target materials, making low temperature calorimetric detectors ideal for a variety of particle physics applications. Rare event searches have continued to require ever greater exposures, which has driven them to ever larger cryogenic detectors, with the CUORE experiment being the first to reach a tonne-scale, mK-cooled, experimental mass. CUORE, designed to search for neutrinoless double beta decay, has been operational since 2017 at a temperature of about 10 mK. This result has been attained by the use of an unprecedentedly large cryogenic infrastructure called the CUORE cryostat: conceived, designed and commissioned for this purpose. In this article the main characteristics and features of the cryogenic facility developed for the CUORE experiment are highlighted. A brief introduction of the evolution of the field and of the past cryogenic facilities are given. The motivation behind the design and development of the CUORE cryogenic facility is detailed as are the steps taken toward realization, commissioning, and operation of the CUORE cryostat. The major challenges overcome by the collaboration and the solutions implemented throughout the building of the cryogenic facility will be discussed along with the potential improvements for future facilities. The success of CUORE has opened the door to a new generation of large-scale cryogenic facilities in numerous fields of science. Broader implications of the incredible feat achieved by the CUORE collaboration on the future cryogenic facilities in various fields ranging from neutrino and dark matter experiments to quantum computing will be examined., Comment: 45 pages, 14 figures

A search for the β+β+, β+/EC, and EC/EC decays of 106Cd was performed at the Modane Underground Laboratory (France) located at a depth of 4800 m w.e. using a TGV-2 multidetector germanium spectrometer. A preliminary evaluation is performed of the experimental data accumulated during the measurements (12 900 h) of ∼13.6 g of 106Cd (with an enrichment of 75%) and the spectrometer background without samples and with samples of natural Cd. New limits (at a 90% confidence level) of half-lives are obtained: T 1/2 ⩾ 1.7 × 1020 yr and T 1/2 ⩾ 1.6 × 1020 yr for the 0νEC/EC resonant decay of 106Cd to the 2741 keV and 2718 keV excited states of the daughter nucleus 106Pd and T 1/2 ⩾ 4.2 × 1020 yr for the 2νEC/EC decay to the ground state of 106Pd (0+ → 0+, g.s.). The limits for other branches of the double beta decay of 106Cd with transitions to the ground and excited states of 106Pd are improved.

The Tri-Bi-Maximal pattern has been long investigated as the symmetric scenario that lies behind the neutrino mixing matrix. It predicts a null reactor angle and hence forbids $CP$ violation in the lepton sector, which is in contrast to the current experimental determinations. We explore different deviations from this pattern to restore the compatibility with the latest fits of neutrino mixing parameters. We consider two unitary matrices to correct the symmetric pattern, each of them is written in terms of one single angle and one complex phase, which will be constrained by the experimental mixings and from symmetry restrictions in the mass matrix. We note that these correction parameters would allow us to obtain simultaneous information about the Dirac and Majorana $CP$ phases in some specific scenarios. We show that the predicted values lead to sharped regions for the neutrinoless double beta decay amplitude, in the selected cases, that could be tested with forthcoming results., Comment: 24 pages, 19 figures

We analyze the consistency of electroweak breaking, neutrino and dark matter phenomenology within the simplest scoto-seesaw model. By adding the minimal dark sector to the simplest "missing partner" type-I seesaw one has a physical picture for the neutrino oscillation lengths: the "atmospheric" mass scale arises from the tree-level seesaw, while the "solar" scale is induced radiatively, mediated by the dark sector. We identify parameter regions consistent with theoretical constraints, as well as dark matter relic abundance and direct detection searches. Using two-loop renormalization group equations we explore the stability of the vacuum and the consistency of the underlying dark parity symmetry. One also has a lower bound for the neutrinoless double beta decay amplitude., 26 pages, 9 figures

In this work we have re-investigated two different kinds of texture zero ansatz of the low energy neutrino mass matrix in view of the Dark-Large-Mixing-Angle (DLMA) solution of the solar neutrino problem which can arise in the presence of non-standard interactions. In particular we revisit the cases of (i) one zero mass matrices when the lowest neutrino mass is zero and (ii) one zero texture with a vanishing minor. In our study we find that for most of the cases, the texture zero conditions which are allowed for the LMA solution, are also allowed for the DLMA solution. However, we found two textures belonging to the case of one zero texture with a vanishing minor where LMA solution does not give a viable solution whereas DLMA solution does. We analyze all the possible texture zero cases belonging to these two kinds of texture zero structures in detail and present correlations between different parameters. We also present the predictions for the effective neutrino mass governing neutrino-less double beta decay for the allowed textures., Comment: 18 pages, 5 figures. To appear in Nucl. Phys. B

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.

Neutrinoless double-beta decay is a forbidden, lepton-number-violating nuclear transition whose observation would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. In this review, we summarize the theoretical progress to understand this process, the expectations and implications under various particle physics models, as well as the nuclear physics challenges that affect the precise predictions of the decay half-life. We will also provide a synopsis of the current and future large-scale experiments that aim at discovering this process in physically well-motivated half-life ranges., 35 pages; Submitted for publication in the Annual Review of Nuclear and Particle Science, Volume 69

The double-electron capture and the electron capture with positron emission in 168Yb have been investigated for the first time at the STELLA facility of the Gran Sasso underground laboratory (Italy) measuring 371 g of highly purified ytterbium oxide placed on the end-cap of a 465 cm3 ultra-low-background high purity Germanium detector (HPGe). No gamma associated to double beta processes in 168Yb have been observed after 2074 h of data taking. This has allowed setting the half-life limits on the level of lim ⁡ T 1 / 2 ∼ 10 14 – 10 18 yr at 90% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in 168Yb to the ( 2 ) − 1403.7 keV excited state of 168Er is set as T 1 / 2 ≥ 1.9 × 10 18 yr at 90% C.L. Half-life limits T 1 / 2 2 ν ( 0 ν ) ≥ 4.5 ( 4.3 ) × 10 16 yr were set on the 2 ν ( 0 ν ) 2 β − decay of 176Yb to the 2 + 84.3 keV first excited level of 176Hf.

LZ is a second-generation Dark Matter experiment to conduct searches for weakly interacting massive particles . It is expected that the detector will reach a sensitivity for spin-independent elastic WIMP-nucleon cross-section of 1 . 6 × 1 0 − 48 cm 2 at a mass of 40 GeV/c 2 in 1000 days of operation. Aside from Dark Matter particle interactions, the detector will also be sensitive to solar and supernova neutrinos as well as neutrinoless double beta decay from 136Xe. Background sources such as 222Rn and 85Kr must be significantly suppressed. This will be assured by radioactive screening of detector components and purification of xenon. The design of the LZ detector, radioactive background expectations and projected WIMP sensitivity are presented in this article.

A new $\mu$TCA DAQ system was introduced in CANDLES experiment with SpaceWire-to-GigabitEthernet (SpaceWire-GigabitEthernet) network for data readout and Flash Analog-to-Digital Converters (FADCs). With SpaceWire-GigabitEthernet, we can construct a flexible DAQ network with multi-path access to FADCs by using off-the-shelf computers. FADCs are equipped 8 event buffers, which act as de-randomizer to detect sequential decays from the background. SpaceWire-GigabitEthernet has high latency (about 100 $\mu$sec) due to long turnaround time, while GigabitEthernet has high throughput. To reduce dead-time, we developed the DAQ system with 4 "crate-parallel" (modules in crates are read in parallel) reading threads. As a result, the readout time is reduced by 4 times: 40 msec down to 10 msec. With improved performance, it is expected to achieve higher background suppression for CANDLES experiment. Moreover, for energy calibration, "event-parallel" reading process (events are read in parallel) is also introduced to reduce measurement time. With 2 "event-parallel" reading processes, the data rate is increased 2 times., Comment: 21st Real Time Conference (2018), Williamsburg, Virginia, USA. 8 pages, 13 figures, 3 tables, 22 references

We construct phenomenologically viable models of lepton masses and mixing based on modular $A_4$ invariance broken to residual symmetries $\mathbb{Z}^{T}_3$ or $\mathbb{Z}^{ST}_3$ and $\mathbb{Z}^S_2$ respectively in the charged lepton and neutrino sectors. In these models the neutrino mixing matrix is of trimaximal mixing form. In addition to successfully describing the charged lepton masses, neutrino mass-squared differences and the atmospheric and reactor neutrino mixing angles $\theta_{23}$ and $\theta_{13}$, these models predict the values of the lightest neutrino mass (i.e., the absolute neutrino mass scale), of the Dirac and Majorana CP violation(CPV) phases, as well as the existence of specific correlations between i) the values of the solar neutrino mixing angle $\theta_{12}$ and the angle $\theta_{13}$ (which determines $\theta_{12}$), ii) the values of the Dirac CPV phase $\delta$ and of the angles $\theta_{23}$ and $\theta_{13}$, iii) the sum of the neutrino masses and $\theta_{23}$, and iv) between the two Majorana phases., Comment: Figure is replaced. Discussions and References are added

Publisher's version (útgefin grein), We consider numerical fits to non-supersymmetric SO(10)-based models in which neutrino mass is generated by the type-I or type-II seesaw mechanism or a combination of both. The fits are performed with a sophisticated top-down procedure, taking into account the renormalization group equations of the gauge and Yukawa couplings, integrating out relevant degrees of freedom at their corresponding mass scales, and using recent data for the Standard Model observables. We find acceptable fits for normal neutrino mass ordering only and with neutrino mass generated by either type-I seesaw only or a combination of types I and II seesaw in which type-I seesaw is dominant. Furthermore, we find predictions from the best fit regarding the small neutrino masses, the effective neutrinoless double beta decay mass, and the leptonic CP-violating phase. Finally, we show that the fits are rather insensitive to the chosen value of the unification scale., The authors wish to thank Sofiane M. Boucenna for collaboration in early stages of this project. T.O. acknowledges support by the Swedish Research Council (Vetenskapsr˚adet) through contract No. 2017-03934 and the KTH Royal Institute of Technology for a sabbatical period at the University of Iceland. M.P. thanks “Stiftelsen Olle Engkvist Byggm¨astare” and “Roland Gustafssons Stiftelse f¨or teoretisk fysik” for financial support. Numerical computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at PDC Center for High Performance Computing (PDC-HPC) at KTH Royal Institute of Technology in Stockholm, Sweden under project numbers PDC-2018-49 and SNIC 2018/3-559.

Because of a high energy of the neutrinoless double-beta decay (0ν2β) of the isotope 150Nd and a high value of the daughter-nucleus charge Zf, 150Nd is one of the most promising isotopes for 0ν2β-decay searches. A 150Nd-containing detector on the basis of a liquid organic scintillator permits employing large isotope masses. Requirements on the radiation purity of the neodymium sample used are determined. The possible design of a large-scale detector of this type and expected results are considered.

Author(s): Mertens, S; Hegai, A; Radford, DC; Abgrall, N; Chan, YD; Martin, RD; Poon, AWP; Schmitt, C | Abstract: High Purity germanium point-contact detectors have low energy thresholds and excellent energy resolution over a wide energy range, and are thus widely used in nuclear and particle physics. In rare event searches, such as neutrinoless double beta decay, the point-contact geometry is of particular importance since it allows for pulse-shape discrimination, and therefore for a significant background reduction. In this paper we investigate the pulse-shape discrimination performance of ultra-high purity germanium point contact detectors. It is demonstrated that a minimal net impurity concentration is required to meet the pulse-shape performance requirements.

In seesaw mechanism, if right handed (RH) neutrino masses are generated dynamically by a gauged U(1) symmetry breaking, a stochastic gravitational wave background (SGWB) sourced by a cosmic string network could be a potential probe of leptogenesis. We show that the leptogenesis mechanism that facilitates the dominant production of lepton asymmetry via the quantum effects of right-handed neutrinos in gravitational background, can be probed by GW detectors as well as next-generation neutrinoless double beta decay (0νββ) experiments in a complementary way. We infer that for a successful leptogenesis, an exclusion limit on f − ΩGWh2 plane would correspond to an exclusion on the |mββ| − m1 plane as well. We consider a normal light neutrino mass ordering and discuss how recent NANOGrav pulsar timing data (if interpreted as GW signal) e.g., at 95% CL, would correlate with the potential discovery or null signal in 0νββ decay experiments.

In this paper, we consider a three-zero texture with diagonal reflection symmetries in the SM. The three-zero texture has two less assumptions ($(M_{u})_{11} , (M_{\nu})_{11} \neq 0$) than the universal four-zero texture of mass matrices $(M_{f})_{11} = (M_{f})_{13,31} = 0$ for $f = u,d,\nu, e$. The texture allows diagonal reflection symmetries to be almost exact and $d$\,-\,$e$ unification. They reproduce the CKM and MNS matrices with accuracies of $O(10^{-4})$ and $O(10^{-3})$. Some perturbative diagonalizations yield two relations with good accuracy for quark mass and mixing. Although this calculation is done in a special basis, it is a general result in a sense, because other textures and generalized $CP$ symmetries exist by some weak basis transformation. By assuming a $d$\,-\,$e$ unified relation ($M_{d} \sim M_{e}$), we obtain the lightest neutrino mass $m_{1} \simeq 2.12\, - \, 5.64\,$[meV] and the effective mass of the double beta decay $|m_{ee}| \simeq 1.23 - 2.15 \,$[meV]., Comment: 18 pages, the final version published in Nuclear Physics B

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, we give updated analyses of DeepCore and SNO data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NO$\nu$A measurements. These new analyses result in more accurate measurements of $\theta_{13}$, $\theta_{12}$, $\Delta m_{21}^2$ and $|\Delta m_{31}^2|$. The best fit value for the atmospheric angle $\theta_{23}$ lies in the second octant, but first octant solutions remain allowed at $\sim2.4\sigma$. Regarding CP violation measurements, the preferred value of $\delta$ we obtain is 1.08$\pi$ (1.58$\pi$) for normal (inverted) neutrino mass ordering. The global analysis prefers normal neutrino mass ordering with 2.5$\sigma$. This preference is milder than the one found in previous global analyses. The new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of $2.00\sigma$. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to $2.68\sigma$ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference, namely $2.70\sigma$. This very same cosmological data set provides $2\sigma$ upper limits on the total neutrino mass corresponding to $\sum\nu, Comment: 35 pages, 15 figures, 3 tables, version 2 includes updated analyses of reactor and accelerator data, matches version accepted for publication in JHEP

[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

Beta decay is one of the first observed [1] and, to date, most studied phenomenon in subatomic physics. It is a spontaneous process occurring in atomic nuclei composed of particular arrangements of...

We study the connection between dark matter (DM) and neutrinoless double beta ($0\nu\beta\beta$) decay in a scotogenic model with hybrid texture in the neutrino mass matrix. Characteristically, the framework allows to write all the non-zero elements of the mass matrix proportional to effective Majorana mass $\left|M_{ee}\right|$. The overall scale of the neutrino mass is found to be governed by non-zero $\left|M_{ee}\right|$. We have obtained interesting correlations of relic density of DM($\Omega h^2$) with DM mass $M_1$ and $\left|M_{ee}\right|$. Using experimental value of DM relic density($\Omega h^2$), the DM mass $M_1$, is found to be $\mathcal{O}$(1TeV) which is within reach of collider experiments. Specifically, for all five hybrid textures, the range of upper bound on DM mass $M_1$ is found to be ($2.27$-$5.31$)TeV. Another interesting feature of the model is the existence of lower bound on $|M_{ee}|$ for all allowed hybrid textures except texture $T_5$ which can be probed in current and future $0\nu\beta\beta$ decay experiments. With high sensitivities, these experiments shall establish the theoretical status of the proposed model. For example, the non-observation of $0\nu\beta\beta$ decay down to the sensitivity $\mathcal{O}(0.03)$eV will refute $T_3$ hybrid texture., Comment: 15 pages, 2 figures

NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross-section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the fact that the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave functions in the two types of processes and the formal similarity of the transition operators. The main experimental tools for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer at the INFN-LNS laboratory. However, the tiny values of DCE cross-sections and the resolution requirements demand beam intensities much higher than those manageable with the present facility. The on-going upgrade of the INFN-LNS facilities promoted by the POTLNS a project in this perspective is intimately connected to the NUMEN project. This paper describes the solutions proposed as a result of the R&D activity performed during the recent years. The goal is to develop suitable technologies allowing for the measurements of DCE cross-section under extremely high beam intensities. a PIR01_00005 — potenziamento dell’infrastruttura di ricerca Laboratori Nazionali del Sud per la produzione di fasci di ioni ad alta intensitá.

We combine $SU(5)$ Grand Unified Theories (GUTs) with $A_4$ modular symmetry and present a comprehensive analysis of the resulting quark and lepton mass matrices for all the simplest cases. Classifying the models according to the representation assignments of the matter fields under $A_4$, we find that there are seven types of $SU(5)$ models with $A_4$ modular symmetry. We present 53 benchmark models with the fewest free parameters. The parameter space of each model is scanned to optimize the agreement between predictions and experimental data, and predictions for the masses and mixing parameters of quarks and leptons are given at the best fitting points. The best fit predictions for the leptonic CP violating Dirac phase, the lightest neutrino mass and the neutrinoless double beta decay parameter when displayed graphically are observed to cover a wide range of possible values, but are clustered around particular regions, allowing future neutrino experiments to discriminate between the different types of models., Comment: 57 pages, 4 figures

It is firmly believed that a signal of neutrinoless double beta decay can unquestionably confirm the Majorana nature of neutrinos. However we notice that a Majorana neutrino mass induced after some neutrinoless double beta decay processes can be accidentally cancelled by another Majorana neutrino mass induced before any neutrinoless double beta decay processes. This realistic cancellation can simultaneously allow an observable neutrinoless double beta decay and a vanishing Majorana neutrino mass. In consequence a future discovery of neutrinoless double beta decay cannot fully rule out the possibility of Dirac neutrinos., Comment: 4 pages, 5 figures

The various global analyses of available neutrino oscillation data indicate the presence of the standard $3+0$ neutrino oscillation picture. However, there are a few short baseline anomalies that point to the possible existence of a fourth neutrino (with mass in the eV-scale), essentially sterile in nature. Should sterile neutrino exist in nature and its presence is not taken into consideration properly in the analyses of neutrino data, the interference terms arising due to the additional CP phases in presence of a sterile neutrino can severely impact the physics searches in long baseline (LBL) neutrino oscillation experiments. In the current work we consider one light (eV-scale) sterile neutrino and probe all the three CP phases ($\delta_{13}$, $\delta_{24}$, $\delta_{34}$) in the context of the upcoming Deep Underground Neutrino Experiment (DUNE) and also estimate how the results improve when data from NOvA, T2K and T2HK are added in the analysis. We illustrate the $\Delta \chi^2$ correlations of the CP phases among each other, and also with the three active-sterile mixing angles. Finally, we briefly illustrate how the relevant parameter spaces in the context of neutrinoless double beta decay get modified in light of the bounds in presence of a light sterile neutrino., Comment: 25 pages; 10 figures; added more details about simulation, prior and event spectra; corrected NDBD analysis; accepted for publication in JHEP

We discuss the $SU(5)$ grand unified extension of flavour models with multiple modular symmetries. The proposed model involves two modular $S_4$ groups, one acting in the charged fermion sector, associated with a modulus field value $\tau_T$ with residual $Z_3^T$ symmetry, and one acting in the right-handed neutrino sector, associated with another modulus field value $\tau_{SU}$ with residual $Z_2^{SU}$ symmetry. Quark and lepton mass hierarchies are naturally generated with the help of weightons, which are SM singlet fields, where their non-zero modular weights play the role of Froggatt-Nielsen charges. The model predicts TM$_1$ lepton mixing, and neutrinoless double beta decay at rates close to the sensitivity of current and future experiments, for both normal and inverted orderings, with suppressed corrections from charged lepton mixing due to the triangular form of its Yukawa matrix., Comment: 24 pages, 4 figures, 3 tables, refs and comments added, published in JHEP

Double-beta processes in $^{184}$Os and $^{192}$Os were searched for over 15851 h at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. by using a 118 g ultra-pure osmium sample installed on the endcap of a 112 cm$^3$ ultra-low-background broad-energy germanium detector. New limits on double-electron capture and electron capture with positron emission in $^{184}$Os were set at the level of $\lim T_{1/2} \sim 10^{16}-10^{17}$ yr. In particular the $2\nu$2K and $2\nu$KL decays of $^{184}$Os to the ground state of $^{184}$W are restricted as $T_{1/2}\geq3.0\times 10^{16}$ yr and $T_{1/2}\geq2.0\times 10^{16}$ yr, respectively. A lower limit on the half-life for the double-beta decay of $^{192}$Os to the first excited level of $^{192}$Pt was set as $\lim T_{1/2}=2.0\times 10^{20}$ yr at 90\% C.L., Comment: 22 pages, 9 figures, 2 tables

We study the impact of maximal zeros of the Dirac mass matrix on neutrino phenomenology and dark matter within the framework of an inverse seesaw ISS $(2,3)$. ISS $(2,3)$ is obtained by adding two right handed neutrinos and three gauge singlets sterile fermions to the standard model leading to an extra sterile state in the keV range. The model is more predictive because of the presence of fewer numbers of right handed neutrinos than the conventional inverse seesaw. Moreover, texture zeros in the structures of the mass matrices involved in the model can reduce the free parameters. We extensively study the effect of different textures of Dirac mass matrix on sterile neutrino dark matter phenomenology. Our study also includes the implications of these texture zero mass matrices on low energy phenomena like neutrinoless double beta decay (0$\nu\beta\beta$). The zero textures highly constrain the parameter space of the model. Based on the allowed cosmological ranges of the relic abundance, decay rates, and dark matter mixing with the active neutrinos, we study the viability of the different textures within the framework., Comment: 31 pages, 11 figures, 4 tables, new references are added, accepted to appear in NPB

Neutrinoless double beta-decay(DBD) is of current interest in high-sensitivity frontiers of particle physics. The decay is very sensitive to Majorana neutrinos masses, neutrino CP phases, right-handed weak interactions and others, which are beyond the standard electro-weal model. DBDs are actually ultra-rare events, and thus DBD experiments with ultra-high sensitivity are required. Critical discussions are presented on nuclear and detector sensitivities for high-sensitivity DBD experiments to study the neutrino masses in the normal and inverted hierarchies., 5 figures

Heavy ion double charge exchange reactions are described by sequential meson-exchange, corresponding to a double single charge exchange (DSCE) reaction mechanism. The theoretical formulation is discussed. The fully quantum mechanical distorted wave 2-step calculations are shown to be reproduced very well by approximating the intermediate propagator by its pole part. The role of ion-ion elastic interactions is discussed. As a first application, calculations are performed for the reaction Ca40(O18,Ne18)40Ar at 15 AMeV. Results are compared to the data measured at LNS by the NUMEN Collaboration. Formal analogies between the nuclear matrix elements (NME) involved in DSCE reactions and in double β-decay are pointed out.

In light of the improved sensitivities of cosmological observations, we examine the status of quasi-degenerate neutrino mass scenarios. Within the simplest extension of the standard cosmological model with massive neutrinos, we find that quasi-degenerate neutrinos are severely constrained by present cosmological data and neutrino oscillation experiments. % % We find that Planck 2018 observations of cosmic microwave background (CMB) anisotropies disfavour quasi-degenerate neutrino masses at $2.4$ Gaussian $\sigma$'s, while adding Baryon acoustic oscillations (BAO) data brings the rejection to 5.9$\sigma$'s. % The highest statistical significance with which one would be able to rule out quasi-degeneracy would arise if the sum of neutrino masses is $\Sigma m_\nu = 60$ \meV (the minimum allowed by neutrino oscillation experiments); % indeed a sensitivity of 15 meV, as expected from a combination of future cosmological probes, would further improve the rejection level up to 17$\sigma$. % We discuss the robustness of these projections with respect to assumptions on the underlying cosmological model, and also compare them with bounds from $\beta$ decay endpoint and neutrinoless double beta decay studies., Comment: 19 pages, 6 figures, 1 table

We make an attempt to study the present status of the tetra-maximal neutrino mixing (TMM) pattern. It predicts all the three leptonic mixing angles $\theta_{13} \approx 8.4^\circ, \theta_{12} \approx 30.4^\circ, $ and $\theta_{23} = 45^\circ $ together with the three CP-violating phases $ - \delta = \rho = \sigma = 90^\circ $. However, the latest global analysis of neutrino oscillation data prefer relatively higher best-fit value of $ \theta_{12} $ as well as non-maximal values of both $ \theta_{23}, \delta $. In order to explain the realistic data, we study the breaking of TMM pattern. We first examine the breaking of TMM due to renormalization group (RG) running effects and then study the impact of explicit breaking terms. We also examine the effect of RG-induced symmetry breaking on the effective Majorana neutrino mass in neutrinoless double beta decay experiments., Comment: 8 pages, 3 figures

We perform a systematic investigation of the texture structures of Majorana neutrino mass matrix Mν having two texture zeros and an equality between two nonzero matrix elements, in the light of recent neutrino oscillation data. Among forty-two possible textures, it is found that only eight textures are compatible with the current experimental data at 3σ C.L. Out of these phenomenologically viable textures, six follow normal mass ordering while remaining two satisfy the inverted mass ordering of neutrino mass spectrum. In the numerical analysis, we carry out a scan over the possible space of all viable patterns. We present the implications of each allowed patterns for three mixing angles (solar, reactor and atmospheric), leptonic CP-violation, neutrino mass scale and the neutrinoless double beta decay indicating strong correlations between oscillation parameters. The symmetry realization of one of the viable textures is also presented.

We study the new physics contributions to neutrinoless double beta decay (0νββ) in a TeV scale left-right model with spontaneous D-parity breaking mechanism where the values of the SU(2)L and SU(2)R gauge couplings, gL and gR are unequal. Neutrino mass is generated in the model via gauge extended inverse seesaw mechanism. We embed the model in a non-supersymmetric SO(10) GUT with a purpose of quantifying the results due to the condition gL≠gR. We compare the predicted numerical values of half life of 0νββ decay, effective Majorana mass parameter and other lepton number violating parameters for three different cases; (i) for manifest left-right symmetric model (gL=gR), (ii) for left-right model with spontaneous D parity breaking (gL≠gR), (iii) for Pati-Salam symmetry with D parity breaking (gL≠gR). We show how different contributions to 0νββ decay are suppressed or enhanced depending upon the values of the ratio gRgL that are predicted from successful gauge coupling unification.

[EN] High pressure xenon Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification are being proposed for rare event detection such as directional dark matter, double electron capture and double beta decay detection. The discrimination of the rare event through the topological signature of primary ionisation trails is a major asset for this type of TPC when compared to single liquid or double-phase TPCs, limited mainly by the high electron diffusion in pure xenon. Helium admixtures with xenon can be an attractive solution to reduce the electron diffu- sion significantly, improving the discrimination efficiency of these optical TPCs. We have measured the electroluminescence (EL) yield of Xe-He mixtures, in the range of 0 to 30% He and demonstrated the small impact on the EL yield of the addition of helium to pure xenon. For a typical reduced electric field of 2.5 kV/cm/bar in the EL region, the EL yield is lowered by similar to 2%, 3%, 6% and 10% for 10%, 15%, 20% and 30% of helium concentration, respectively. This decrease is less than what has been obtained from the most recent simulation framework in the literature. The impact of the addition of helium on EL statistical fluctuations is negligible, within the experimental uncertainties. The present results are an important benchmark for the simulation tools to be applied to future optical TPCs based on Xe-He mixtures., 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 Economa y Competitividad of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program SEV-2014-0398 and the Mara 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; the U.S. Department of Energy under contracts number DEAC02-06CH11357 (Argonne National Laboratory), DE-AC0207CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A& M) and DE-SC0019223/DESC0019054 (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.

CAlcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double beta decay of $^{48}$Ca using a CaF$_2$ scintillator array. A high Q-value of $^{48}$Ca at 4,272 keV enabled us to achieve very low background condition, however, at the same it causes difficulties in calibrating the detector's Q-value region because of the absence of a standard high-energy $\gamma$-ray source. Therefore, we have developed a novel calibration system based on $\gamma$-ray emission by neutron capture on $^{28}$Si, $^{56}$Fe and $^{58}$Ni nuclei. In the paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV., Comment: 6 pages, 7 figures

The alternative renormalizable minimal SO(10) model is composed of the Yukawa couplings with 10⊕120 Higgs fields, whereas the right-handed (RH) neutrino Majorana masses are generated via the Witten mechanism. The gauge coupling unification is achieved together with a unique pattern of the fermion masses and mixing at the grand unification scale due to additional contributions of vector-like quarks to the standard model renormalization group equations. We perform the fitting of the model to the experimental data of charged fermion masses and the CKM matrix. The best fit point is obtained with large pulls for mc, ms, mb, and mτ. For the modifications to the minimal model by adding either 10′ or 120′, a large deviation for the tau mass rules out all these models. In the case with the bottom and vector-like quark mixing, the mass matrices are well fitted the charged fermions but the bound on the light neutrino mass scale excludes this scenario. To ameliorate this deficit, we consider the two-step symmetry breaking scenario, SO(10)→SU(5)→SU(3)C×SU(2)L×U(1)Y, with the SO(10) breaking at the Planck scale leading to the radiatively generated RH neutrino Majorana masses being at the ordinary seesaw scale. For this case, we find the best fit point with χ2=7.8 consistent with experimental results including the neutrino sector. The largest deviation is 2.3σ corresponding to the strange quark mass. Hence, a more precise determination of the strange quark mass can test this model. For the best fit point, we find the effective Majorana neutrino mass of mββ=0.22 meV and the sum of light neutrino masses as Σ=0.078 eV, which are consistent with the current constraints from the search for the neutrinoless double beta decay and the CMB anisotropy measurement.

Two-neutrino double-beta-decay matrix elements M 2 ν and single beta-decay branching ratios were calculated for 48Ca and 96Zr in the interacting nuclear shell model using large single-particle valence spaces with well-tested two-body Hamiltonians. For 48Ca the matrix element M 2 ν = 0.0511 is obtained, which is 5.5% smaller than the previously reported value of 0.0539. For 96Zr this work reports the first large-scale shell-model calculation of the nuclear matrix element, yielding a value M 2 ν = 0.0747 with extreme single-state dominance. These matrix elements, combined with the available ββ-decay half-life data, yield effective values of the weak axial coupling which in turn are used to produce in a consistent way the β-decay branching ratios of ( 7.5 ± 2.8 ) % for 48Ca and ( 18.4 ± 0.09 ) % for 96Zr. These are larger than obtained in previous studies, implying that the detection of the β-decay branches could be possible in dedicated experiments sometime in the (near) future.

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, The NEXT collaboration acknowledges funding support from the following agencies and institutions: European Research Council under Advanced Grant 339787-NEXT and Starting Grant 240054-TREX, Spanish Ministerio de Economia y Competitividad under grants Consolider-Ingenio 2010 CSD2008-0037 (CUP) and CSD2007-00042 (CPAN), contracts FPA2008-03456 and FPA2009-13697; Portuguese Fundacao para a Ciencia e a Tecnologia; European FEDER under grant PPTDC/FIS/103860/2008; US Department Of Energy under contract DE-AC02-05CH11231.

We used a high-resolution magnetic spectrograph to study neutron pair-correlated 0 + states in 136Ba, produced via the Ba 138 ( p , t ) reaction. In conjunction with state-of-the-art shell model calculations, these data benchmark part of the dominant Gamow-Teller component of the nuclear matrix element (NME) for 136Xe neutrinoless double beta ( 0 ν β β ) decay. We demonstrate for the first time an evaluation of part of a 0 ν β β decay NME by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of 0 ν β β decay matrix elements.

Matter effects on the mixing of the neutrinos mass eigenstates, also known as the Mikheyev–Smirnov–Wolfenstein effect, seem to be well established in describing the propagation of the neutrino from the source to detecting devices. These effects were mostly considered in bulk matter, but not inside the atoms. Here we consider the effect of the high electron densities existing in the atomic nuclei. We investigate if these effects can affect the known neutrino phenomenology. It was reported that the mixing of the neutrinos in high density matter, such as inside a supernova, can affect the Majoron decay probabilities. We investigate if the neutrino mixing effects in the high electron density inside the atomic nuclei can change the neutrinoless double beta decay half-life formula. In both cases we found that the standard results stand. The results look simple, but the road to them is complex and it opens the possibility that the neutrino mixing in atomic nuclei may affect other observables, such as the neutrinoless double beta Majoron decays.