The NEMO 3 experiment searches for neutrinoless double beta decay and makes precision measurements of two-neutrino double beta decay in seven isotopes. The latest two-neutrino half-life results are presented, together with the limits on neutrinoless half-lives and the corresponding effective Majorana neutrino masses. Also given are the limits obtained on neutrinoless double beta decay mediated by Rp-violating SUSY, right-hand currents and different Majoron emission modes.
The half-life for two-neutrino double beta decay of Nd-150 has been measured with data taken by the NEMO 3 experiment at the Modane Underground Laboratory. The limits are also set on the half-life of different neutrinoless double beta decay of this isotope.
NEMO 3 experiment is designed to search for neutrinoless double beta decay. It is located in the Modane Underground Laboratory (LSM) and has been taking data since February 2003. The half- lives of two neutrino beta decay have been measured for seven isotopes. No evidence of neutrinoless double beta decay has been found. The limits on both the half-lives of the neutrinoless double beta decay and the corresponding Majorana effective masses are derived
The NEMO 3 detector has been running since February 2003 with several double beta emitters. New results are given for Mo100, Se82, Nd150, Zr96, Ca48. The NEMO 3 detector properties are presented for tracking reconstruction, identification of particles, energy measurement. Angular distributions for one and two electrons are produced as well as energy spectra. It is deduced new values of half lives for the double beta emitters and stronger limits on the effective neutrino mass using data on Mo100 and Se82.
Since 2003 the NEMO~3 experiment has been searching for neutrinoless double beta decay using about 10 kg of enriched isotopes. A limit of T_(1/2)(0nu) > 5.8 10**23 years at 90 % CL has been obtained for 100-Mo from the first two years of data. Several measurements of two-neutrino double beta decays have also been performed. A first NEMO 3 measurement of the half-life of 130-Te is presented, giving a value of T_(1/2)(2nu) = (7.6 +- 1.5 (stat) +- 0.8 (syst)) 10**20 years. In parallel, there is an active R&D programme for the SuperNEMO experiment which is expected to commence data taking in 2012-…
The NEMO 3 detector, which has been operating in the Frejus underground laboratory since February 2003, is devoted to the search for neutrinoless double beta decay (bb0nu). Half-lives of the two neutrino double beta decays (bb2nu) have been measured for 100Mo and 82Se. After 389 effective days of data collection from February 2003 until September 2004 (Phase I), no evidence for neutrinoless double beta decay was found from ~7kg of 100Mo and ~1 kg of 82Se. The corresponding lower limits for the half-lives are 4.6 x 10^23 years for 100Mo and 1.0 x10^23 years for 82Se (90% C.L.). Depending on the…
The NEMO-3 tracking detector is located in the Fréjus Underground Laboratory. It was designed to study double beta decay in a number of different isotopes. Presented here are the experimental half-life limits on the double beta decay process for the isotopes $^{100}$Mo and $^{82}$Se for different Majoron emission modes and limits on the effective neutrino-Majoron coupling constants. In particular, new limits on "ordinary" Majoron (spectral index 1) decay of $^{100}$Mo ($T_{1/2} > 2.7\cdot10^{22}$ y) and $^{82}$Se ($T_{1/2} > 1.5\cdot10^{22}$ y) have been obtained. Corresponding bounds on the M…
The NEMO-3 detector, which has been operating in the Frejus Underground Laboratory since February 2003, is devoted to searching for neutrinoless double beta decay (ββ0 ν). The expected performance of the detector has been successfully achieved. Half-lives of the two neutrinos double beta decay (ββ2 ν$) have been measured for ^{100} Mo, ^{82}Se, ^{96}Zr, ^{116}Cd and ^{150}Nd. After 265 days of data collection from February 2003 until March 2004, no evidence for neutrinoless double beta decay (ββ0 ν) was found from \sim 7 kg of ^{100} Mo and \sim 1 kg of ^{82} Se. The corresponding lower limits…
The SuperNEMO project aims to search for neutrinoless double beta decay ($0νββ$) up to a sensitivity of 10$^{26}$ years for the $0νββ$ half-life (down to $\sim$ 50~meV in the effective Majorana neutrino mass), using $\sim$100 kg of source and a `tracko-calo' detector. The current status of the 2006--2010 R\&D programme is discussed here.
The aim of the NEMO 3 experiment is the search for neutrinoless double beta decay and precise measurement of two-neutrino double beta decay of several isotopes. The experiment has been taking data since 2003. Since no evidence for neutrinoless double beta decay of Mo100 and Se82 has been found, a 90% C.L. lower limit on the half-life of this process and corresponding upper limit on the effective Majorana neutrino mass are derived. The data are also interpreted in terms of alternative models, such as weak right-handed currents or Majoron emission. In addition, NEMO 3 has performed precision mea…
The NEMO collaboration is looking to measure neutrinoless double beta decay down to a lower limit of 0.1 eV for the effective neutrino mass. The NEMO 3 detector is now operating in the Frejus Underground Laboratory. The expected performance and the data of the first runs are presented here.
Latest results on $0νββ$, $0νχ^0ββ$ and $2νββ$ decays of different isotopes from NEMO-3 double beta decay experiment are presented. In particular, new limits at 90% C.L. on neurtinoless double beta decay of $^{100}Mo$ and $^{82}Se$ have been obtained, $T_{1/2} > 5.8\times 10^{23}$ y and $T_{1/2} > 2.1\times 10^{23}$ y, respectively.
Latest results on $ββ0 ν$, $ββ0 νχ^0$ and $ββ2 ν$ decays of different isotopes from NEMO-3 double beta decay experiment are presented. In particular, new limits on neurtinoless double beta decay of $^{100}Mo$ and $^{82}Se$ have been obtained, $T_{1/2} > 4.6\times 10^{23}$ y and $T_{1/2} > 1\times 10^{23}$ y, respectively. A possible next step with SuperNEMO detector is discussed.
The NEMO3 detector, now operating in the Frejus Underground Laboratory, is devoted to search for neutrinoless double beta decay; the expected sensitivity for the effective neutrino mass is on the order of 0.1 eV. The performances of the tracking detector are presented. The first and very preliminary results concerning the background and the double beta signal are given.
The NEMO-3 experiment is searching for neutrinoless double beta decay for 2 main isotopes (100Mo and 82Se) and is studying the two-neutrino double beta decay of seven isotopes. The experiment has been taking data since 2003 and, up to the end of 2009, showed no evidence for neutrinoless double beta decay. Two 90 % CL lower limits on the half-lives of the transitions were obtained : T_{1/2}^{0ν} > 1.0 10^{24} yr for 100Mo and T_{1/2}^{0ν} > 3.2 10^{23}$ yr for 82Se. The corresponding limits on the effective Majorana neutrino mass are respectively | m_nu | < 0.47 - 0.96 eV and | m_nu | < 0.94 - …
The half-life for double beta decay of 150-Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of 150-Nd the half-life for 2nubb decay is measured to be T_1/2^2nu = (9.11+0.25_-0.22}(stat.) +- 0.63 (syst.)) x 10^18 years. The observed limit on the half-life for neutrinoless double beta decay is found to be T_1/2^{0nu} > 1.8 x 10^22 years at 90 % Confidence Level. This translates into a limit on the effective Majorana neutrino mass of <m_{neutrino}><4.0-6.3 eV if the nuclear deformation is taken into account. We also…
The NEMO experiment is investigating the neutrinoless double beta decay. The NEMO-3 detector is taking data in the Frejus Underground Laboratory. The goal of the SuperNEMO detector is to reach a sensitivity on the order of 10^26 year on the half-life of the bb0nu process. The chosen isotopes for the future detector are 82Se and 150Nd, because of the reduced background. The collaboration has started a 3-year R&D development on all components : tracking detector, calorimeter, source enrichment and purification, radiopurity measurements.
The NEMO 3 experiment is devoted to the search for neutrinoless double beta decay, as well as for accurate measurement of two-neutrino double beta decay. The detector has been taking data in the LSM laboratory since 2003 and the latest NEMO 3 results for seven double beta decay isotopes are presented here for both decay modes. The SuperNEMO project aims to extend the NEMO technique to a 100-200 kg isotope experiment with the target half-life sensitivity of 1-2 x 10^26 y. The current status of the SuperNEMO R&D programme is described.
The NEMO 3 experiment is located in the Modane Underground Laboratory and has been taking data since 2003 with seven isotopes. It is searching for the double beta decay process with two or zero neutrinos emitted in the final state. Precision measurements of the half-life of the isotopes due to two neutrino double beta decay have been performed and new results for 96Zr, 48Ca and 150Nd are presented here. Measurements of this process are important for reducing the uncertainties on the nuclear matrix elements. No evidence for zero neutrino double beta decay has been found and a 90% Confidence Lev…
The NEMO collaboration is presently mounting the NEMO-3 detector in the Fréjus Underground Laboratory. This detector, which will be completed by the end of the year 2000, is devoted to the search of neutrinoless double beta decay with various isotopes. Much attention has been focused on ^{100}Mo and ^{82}Se with their large Q_{ββ}-values. The detector is based on the direct detection of the two electrons by a tracking device and on the measurement of their energies by a calorimeter. The aim of the experiment is to have a sensitivity for the effective neutrino mass on the order of 0.1 eV. The s…
The observation of neutrino oscillations has proven that neutrinos have mass. This is direct evidence of physics beyond the Standard Model. This discovery has renewed interest in neutrinoless double beta decay ($0νββ$) experiments which provide the only practical way to determine whether neutrinos are Majorana or Dirac particles. Such experiments also have the potential to determine the absolute scale of the neutrino mass and help resolve the neutrino mass hierarchy question. The NEMO-3 (Neutrino Ettore Majorana Observatory) is currently one of the most sensitive searches for neutrinoless doub…
We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-$β$ decay of $^{150}$Nd using a total exposure of $0.19$ kg$\cdot$y recorded with the NEMO-3 detector at the Modane Underground Laboratory (LSM). We find no evidence of this decay and set lower limits on the half-life in the range $T_{1/2}>(1.1-3.2)\times10^{21}$ y at the $90\%$ CL, depending on the model used for the kinematic distributions of the emitted electrons.
In some models beyond the Standard Model where lepton number violation by two units is forbidden (implying neutrinos cannot be Majorana fermions), violation by four units can still occur, allowing neutrinoless quadruple beta decay. The isotope 150-Nd is one of the very few isotopes where this process could be experimentally observed. The experimental signature consists of four electrons with a total energy equal to the Q-value of the decay. The NEMO-3 experiment in the Modane Underground Laboratory in France ran from 2003 to 2011, and studied seven isotopes of interest including 150-Nd. This a…
We report the results of a search for the neutrinoless double-$β$ decay (0$νββ$) of $^{100}$Mo, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7 kg.y, no evidence for the 0$νββ$ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of $T_{1/2}(0νββ)>1.1 \times 10^{24}$ years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the Nuclear Matrix Elements this corresponds to an upper limit on the Majorana effective neutrino mass of $< m_ν > < 0.3-0.9$ eV (…
Liquid scintillator experiments for neutrinoless double beta decay search have high sensitivity based on the ultra low background environment and high scalability. This paper describes an overview of current ongoing projects KamLAND-Zen and SNO+.
The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $β$ ($0νββ$) decay. We report final results of a search for $0νββ$ decays with $6.914$ kg of $^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0νββ$ signal region and find no evidence of $0νββ$ decays in the data. The level of observed background in the $0νββ$ signal region $[2.8-3.2]$ MeV is $0.44 …
Neutrinoless double beta decay is a promising test for lepton number violating physics beyond the standard model of particle physics. There is a deep connection between this decay and the phenomenon of neutrino masses. In particular, we will discuss the relation between neutrinoless double beta decay and Majorana neutrino masses provided by the so-called Schechter--Valle theorem in a quantitative way. Furthermore, we will present an experimental cross check to discriminate neutrinoless double beta decay from unknown nuclear background using only one isotope, i.e., within one experiment.
Neutrinoless double beta decay is a lepton number violating process whose observation would also establish that neutrinos are their own anti-particles. There are many experimental efforts with a variety of techniques. Some (EXO, Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has reported the first measurement of the half life for the double beta decay with two neutrinos of $^{136}$Xe. The sensitivities of the different proposals are reviewed.
In the Standard Model the total lepton number is conserved. Thus, neutrinoless double-beta decay, in which the total lepton number is violated by two units, is a probe of physics beyond the Standard Model. In this review we consider the basic mechanism of neutrinoless double-beta decay induced by light Majorana neutrino masses. After a brief summary of the present status of our knowledge of neutrino masses and mixing and an introduction to the seesaw mechanism for the generation of light Majorana neutrino masses, in this review we discuss the theory and phenomenology of neutrinoless double-bet…
In this brief review we discuss the generation of Majorana neutrino masses through the see-saw mechanism, the theory of neutrinoless double-beta decay, the implications of neutrino oscillation data for the effective Majorana mass, taking into account the recent Daya Bay measurement of theta_13, and the interpretation of the results of neutrinoless double-beta decay experiments.
The search for neutrinoless double-beta decay is important in determining the Majorana nature of the neutrino, and also in establishing if lepton number is violated. In this work, we combine the published data from five independent neutrinoless double-beta decay experiments: CUORICINO, EXO, GERDA, KamLAND-Zen and NEMO-3. As these experiments use different isotope sources, the relative signal normalisation between them depends on the Nuclear Matrix Element (NME) calculations used. The combined limits for the Majorana neutrino mass for 5 different NME models range from 130-310 meV. The combined …
We present a concise formula to relate the effective mass term of the neutrinoless double beta decay to a single neutrino mass, two Majorana CP-violating phases and four observables of neutrino oscillations for a generic neutrino mass spectrum. If the alleged evidence for the neutrinoless double beta decay is taken into account, one may obtain a rough but model-independent constraint on the absolute scale of neutrino masses -- it is most likely to be in the range between 0.1 eV and 1 eV.
The search for neutrinoless double beta decay is a rich source for new physics. The observation of this decay will lead to understanding of the absolute mass scale of neutrinos, the Majorana nature of the neutrino (whether the neutrino is its own anti-particle), and lepton number violation. Double beta decay is being investigated around the world by several experiments using different candidate isotopes. There has been much progress made in experimental techniques recently such that achieving sensitivity to neutrino masses at 50 meV and below will be possible in the near future. A summary of r…
In the minimal supersymmetric extension to the Standard Model, a non-zero lepton number violating coupling lambda'_111 predicts both neutrinoless double beta decay and resonant single slepton production at the LHC. We show that, in this case, if neutrinoless double beta decay is discovered in the next generation of experiments, there exist good prospects to observe single slepton production at the LHC. Neutrinoless double beta decay could otherwise result from a different source (such as a non-zero Majorana neutrino mass). Resonant single slepton production at the LHC can therefore discriminat…
Recent considerations by these authors pointed out the attractive features which a search for the exchange of heavy Majorana neutrinos could have for solving the mass and the lepton number puzzles for all neutrinos, in TeV-level electron-electron scattering. In the present note, we show that, contrary to subsequently published arguments, non-observation of neutrinoless double beta decay has, to date, no bearing on the promise of this important task for future linear electron colliders.
We discuss the contribution of right-handed neutrinos (RHNs) to the effective neutrino mass of the neutrinoless double beta decay within the minimal type-I seesaw model using the intrinsic seesaw relation of neutrino mass and mixing parameters and the relative mass dependence of the nuclear matrix elements. In the viable parameter space, we find the possibilities of both the enhancement and cancellation to the effective neutrino mass from RHNs. The bounds on the parameter space of the RHNs can be determined with the effective neutrino mass extracted from neutrinoless double beta decay experime…
Recent neutrino experiment results show a preference for the normal neutrino mass ordering. The global efforts to search for neutrinoless double beta decays undergo a broad gap with the approach to the prediction in the three-neutrino framework based on the normal ordering. This research is intended to show that it is possible to find a neutrinoless double beta decay signal even with normal ordered neutrino masses. We propose the existence of a light sterile neutrino as a solution to the higher effective mass of the electron neutrino expected by the current experiments. A few short-baseline os…
The search for neutrinoless double beta decay ($0νββ$) is one of the key experiments for determining unresolved properties of neutrinos. Experimental observation of $0νββ$ would provide a clear demonstration of the Majorana nature of neutrinos and a lepton number violating process in particle physics. This report is a brief review describing the $0νββ$ process and its significance. The detector technologies used in the present and proposed $0νββ$ experiments are compared among their recent experimental results. Moreover, the sensitivities for $0νββ$ discovery in a number of present and propose…
This Letter reports results from the NEMO-3 experiment based on an exposure of 1275 days with 661g of 130Te in the form of enriched and natural tellurium foils. The double beta decay rate of 130Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T1/2 = (7.0 +/- 0.9(stat) +/- 1.1(syst)) x 10^{20} yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.
The Large Hadron Collider has a potential to probe the scale of left-right symmetry restoration and the associated lepton number violation. Moreover, it offers hope of measuring the right-handed leptonic mixing matrix. We show how this, together with constraints from lepton flavor violating processes, can be used to make predictions for neutrinoless double beta decay. We illustrate this deep connection in the case of the type-II seesaw.
This paper reviews the current status and future outlook of neutrinoless double beta decay searches, which try to provide an answer to the fundamental question of whether neutrinos are Dirac or Majorana particles.
We investigate the half-life expectations for neutrinoless double beta decay by applying statistical distributions of neutrino mixing observables, neutrino mass constraints from cosmology and nuclear matrix elements. The analysis is performed in the standard scenario of active Majorana neutrino exchange, when light sterile neutrinos are added, and within TeV-scale left-right symmetric frameworks. The latter two cases correspond to a modified phenomenology of double beta decay for a normal and inverted mass ordering, and thus different discovery potential for future experiments.
Probing neutrinoless double beta decay is one of the primary goals for SNO+, SNOLAB's multi-purpose neutrino detector. In order to achieve this goal the SNO detector has been adapted so that it can be filled with Te-loaded liquid scintillator. During the initial double beta phase the target loading is 0.3% natural Te, which equates to $\sim790$ kg of double beta isotope. Estimating the sensitivity to neutrinoless double beta decay requires a well understood background model. For SNO+ this is provided by a comprehensive study considering all possible background contributions, whether they origi…
We consider perturbative one loop QCD corrections to the light neutrino contribution to neutrinoless double beta decay and find large enhancement to the rate. QCD corrections also generate structures which mimic new physics contributions usually considered. Within some approximations, the net effect seem to almost saturate the experimental limits, and therefore seems to implt that this is all there is to neutrinoless double beta decay.
We examine how constraints can be placed on the neutrino component of dark matter by an accurate measurement of neutrinoless double beta ($0νββ$) decay and the solar oscillation amplitude. We comment on the alleged evidence for $0νββ$ decay.
Interactions that manifest themselves as lepton number violating processes at low energies in combination with sphaleron transitions typically erase any preexisting baryon asymmetry of the Universe. In this article, we discuss the constraints obtained from an observation of neutrinoless double beta decay in this context. If a new physics mechanism of neutrinoless double beta decay other than the standard light neutrino exchange is observed, typical scenarios of high-scale baryogenesis will be excluded unless the baryon asymmetry is stabilized via some new mechanism. We also sketch how this con…
Experiments in progress may confirm a nonzero neutrinoless double beta decay rate in conflict with the cosmological upper limit on neutrino masses and thus require new physics beyond the Standard Model. A natural candidate is the Left-Right symmetric theory, which led originally to neutrino mass and the seesaw mechanism. In the absence of cancelations of large Dirac Yukawa couplings, we show how such a scenario would require a low scale of Left-Right symmetry breaking roughly below 10 TeV, tantalizingly close to the LHC reach.
A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.
In the event of an observation of neutrinoless double beta decay, a relevant question would be: what lepton number violating physics is responsible for the decay? The exchange of Majorana neutrinos and/or supersymmetric particles may contribute. We point out that measurements of supersymmetric signals at the LHC, including single slepton production, could be used to help bound some supersymmetric processes contributing to neutrinoless double beta decay. LHC information about the supersymmetric spectrum could be combined with Bd-Bd bar mixing data in order to bound a competing neutrinoless doub…
The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-$β$ decay of $^{48}{\rm Ca}$. Using $5.25$ yr of data recorded with a $6.99\,{\rm g}$ sample of $^{48}{\rm Ca}$, approximately $150$ double-$β$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-$β$ decay of $^{48}{\rm Ca}$ has been measured to be $T^{2ν}_{1/2}\,=\,[6.4\, ^{+0.7}_{-0.6}{\rm (stat.)} \, ^{+1.2}_{-0.9}{\rm (syst.)}] \times 10^{19}\,{\rm yr}$. A search for neutrinoless double-$β$ decay of $^{48}{\rm Ca}$ yields…
A measurement of neutrinoless double beta decay in one isotope does not allow to determine the underlying physics mechanism. We discuss the discrimination of mechanisms for neutrinoless double beta decay by comparing ratios of half life measurements for different isotopes. Six prominent examples for specific new physics contributions to neutrinoless double beta decay are analyzed. We find that the change in corresponding ratios of half lives varies from 60% for supersymmetric models up to a factor of 5-20 for extra-dimensional and left-right-symmetric mechanisms.
The detection of neutrinoless double-beta decay will establish the Majorana nature of neutrinos. In addition, if the nuclear matrix elements of this process are reliably known, the experimental lifetime will provide precious information about the absolute neutrino masses and hierarchy. I review the status of nuclear structure calculations for neutrinoless double-beta decay matrix elements, and discuss some key issues to be addressed in order to meet the demand for accurate nuclear matrix elements.
We point out that lepton number violation is possible even if neutrinos are Dirac particles. We illustrate this by constructing a simple model that allows for lepton number violation by four units only. As a consequence, neutrinoless double beta decay is forbidden, but neutrinoless quadruple beta decay is possible: $(A,Z) \to (A,Z+4) + 4 e^-$. We identify three candidate isotopes for this decay, the most promising one being Nd-150 due to its high $Q_{0ν4β}$-value of 2 MeV. Analogous processes, such as neutrinoless quadruple electron capture, are also possible. The expected lifetimes are extrem…
We review the potential to probe new physics with neutrinoless double beta decay $(A,Z) \to (A,Z+2) + 2 e^-$. Both the standard long-range light neutrino mechanism as well as short-range mechanisms mediated by heavy particles are discussed. We also stress aspects of the connection to lepton number violation at colliders and the implications for baryogenesis.
Neutrinoless double beta decay is a process of fundamental importance for particle physics. It can be mediated by light massive Majorana neutrinos (standard interpretation) or by something else (non-standard interpretations). We review its dependence on the neutrino parameters, its complementarity to other observables sensitive to neutrino mass, and emphasize its ability to distinguish different neutrino mass models. Then we discuss mechanisms different from light Majorana neutrino exchange, and show what can be learned from those and how they could be tested.
We analyze the constraints on neutrino mass spectra with extra sterile neutrinos as implied by the LSND experiment. The various mass related observables in neutrinoless double beta decay, tritium beta decay and cosmology are discussed. Both neutrino oscillation results as well as recent cosmological neutrino mass bounds are taken into account. We find that some of the allowed mass patterns are severely restricted by the current constraints, in particular by the cosmological constraints on the total sum of neutrino masses and by the non-maximality of the solar neutrino mixing angle. Furthermore…
This paper presents a review of the search for neutrinoless double beta decay of $^{76}$Ge with emphasis on the recent results of the GERDA experiment. It includes an appraisal of fifty years of research on this topic as well as an outlook.
Of the many extensions to the standard model that could possibly generate neutrino mass, most necessitate the neutrino being a Majorana fermion. If this is the case, the rare process of neutrinoless double beta decay is predicted with half lives greater than about $10^{25}$ years. Many current and future experiments look for this decay by identifying a summed double beta energy at the Q value of the decay, but adding energy and angular measurements of the individual betas allows the underlying decay mechanism to be probed. A novel nano-tracking detector based on a clever combination of thin fi…
We discuss a mechanism of neutrinoless double beta decay, where neutrinos of different flavours come into play. This is realized by effective flavour-violating scalar interactions. As one consequence, we find that within the normal mass ordering the neutrino effective mass may no longer vanish due to contributions from other flavours. We evaluate the necessary nuclear matrix elements, consider the interference between the standard diagram and the new scalar one, and analyze a UV-complete model that realizes the scalar interaction. Tests of the complete model are possible at colliders and futur…
The connection of neutrino physics with neutrinoless double beta decay is reviewed. After presenting the current status of the PMNS matrix and the theoretical background of neutrino mass and lepton mixing, we will summarize the various implications of neutrino physics for double beta decay. The influence of light sterile neutrinos and other exotic modifications of the three neutrino picture is also discussed.
