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Results for “lepton number violation”
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Probing lepton number violation at same-sign lepton colliders
Same-sign lepton colliders offer a promising environment to probe lepton number violation. We study processes that change lepton number by two units in the context of Majorana heavy neutral leptons and neutrinophilic scalars at μ TRISTAN , a proposed same-sign muon collider. Our work shows that such colliders, with modest energy and luminosity requirements, can either reveal direct evidence of lepton number violation or significantly constrain unexplored regions of parameter space, especially in the case of a neutrinophilic scalar. Published by the American Physical Society 2025
Neutrinoless double beta decay and Lepton Number Violation
Neutrinoless double beta decay and Lepton Number Violation
Search for baryon and lepton number violating decays D → p ℓ
We search for the baryon and lepton number violating charm decays, D → p ℓ , where D is either a D 0 or a D ¯ 0 and ℓ is a muon or an electron, using a data sample of 921 fb − 1 collected by the Belle detector at the KEKB asymmetric energy e + e − collider. In the absence of significant signals, we set upper limits on the branching fractions in the range ( 5 – 8 ) × 10 − 7 at a 90% confidence level, depending on the decay mode. Published by the American Physical Society 2024
TeV-scale lepton number violation: Connecting leptogenesis, neutrinoless double beta decay, and colliders
In the context of TeV-scale lepton number violating (LNV) interactions, we illustrate the interplay between leptogenesis, neutrinoless double beta ( 0 ν β β ) decay, and LNV searches at proton-proton colliders. Using a concrete model for illustration, we overcome the limitations of previous effective field theory analyses and are able to identify the parameter space where standard thermal leptogenesis is rendered unviable due to washout processes. Moreover, we show how 0 ν β β decay and p p collisions provide complementary probes. We find that the new particle spectrum can have a decisive impact on the relative sensitivity of these two probes. Published by the American Physical Society 2024
Search for the baryon- and lepton-number violating decays B 0 → pμ⁻ and $B^0_s$ → pμ⁻
A search for the baryon- and lepton-number violating decays and $B$$^{0}_{s}$ →pμ – is performed at the LHCb experiment using data collected in proton-proton collisions at √s =7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2, and 6 fb –1 , respectively. No significant signal for B 0 → pμ – and $B$$^{0}_{s}$ → pμ – decays is found and the upper limits on the branching fractions are determined to be Β(B 0 → pμ – ) < 2.6(3.1) ×10 –9 and Β($B$$^{0}_{s}$ → pμ – ) < 12.1(14.0) ×10 –9 , respectively, at 90% (95%) confidence level. These are the first limits on these decays to date.
Probing lepton number violation and Majorana nature of neutrinos at the LHC
Abstract Observation of lepton number (L) violation by two units at colliders would provide evidence for the Majorana nature of neutrinos. We study signals ofL-violation in the context of two popular models of neutrino masses, the type-II seesaw model and the Zee model, wherein small neutrino masses arise at the tree-level and one-loop level, respectively. We focus onL-violation signals at the LHC arising through the processpp→ℓ ± ℓ ′± + jets within these frameworks. We obtain sensitivity toL-violation in the type-II seesaw model for triplet scalar masses up to 700 GeV and in the Zee model for charged scalar masses up to 4.8 TeV at the high-luminosity LHC with an integrated luminosity of 3 ab −1 .
Three-nucleon lepton-number-violating potentials in chiral effective field theory and their matrix elements in light nuclei
Here, we derive the three-nucleon neutrinoless double-𝛽 decay potential in a Δ-full chiral effective field theory through next-to-next-to-next-to leading order in Weinberg's power counting. The matrix elements of the resulting operators are computed in light nuclei using variational Monte Carlo with wave functions constructed from the Norfolk family of nuclear interactions. We find that three-nucleon corrections induce a modest quenching of the total nuclear matrix elements. We discuss model dependencies and the potential impact of these corrections on the sensitivity of experimental programs to probe lepton number violating parameters. These results provide a benchmark for many-body methods capable of reaching heavier nuclei of experimental interest.
Search for the baryon number and lepton number violating decays τ − → Λ π − and τ − → Λ ¯ π − at Belle II
We present a search for the baryon number B and lepton number L violating decays τ − → Λ π − and τ − → Λ ¯ π − produced from the e + e − → τ + τ − process, using a 364 fb − 1 data sample collected by the Belle II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have | Δ ( B − L ) | equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of τ − → Λ π − and τ − → Λ ¯ π − are determined to be 4.7 × 10 − 8 and 4.3 × 10 − 8 , respectively. Published by the American Physical Society 2024
Lepton number violation: From 0 ν β β decay to long-lived particle searches
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Search for baryon- and lepton-number violating decays D 0 → p ¯ e + and D 0 → p e −
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First Results on the Search for Lepton Number Violating Neutrinoless Double-𝛽 Decay with the LEGEND-200 Experiment
The LEGEND Collaboration is searching for neutrinoless double-beta (0𝜈𝛽𝛽) decay by operating high-purity germanium detectors enriched in 76 Ge in a low-background liquid argon environment. Building on key technological innovations from the GERmanium Detector Array (GERDA) experiment and the MAJORANA DEMONSTRATOR experiment, LEGEND-200 has performed a first 0𝜈𝛽𝛽 decay search based on 61.0 kg yr of data. Over half of this exposure comes from our highest performing detectors, including newly developed inverted-coaxial detectors, and is characterized by an estimated background level of 0.5$^{+0.3}_{−0.2}$ cts/(keV ton yr) in the 0𝜈𝛽𝛽 decay signal region. A combined analysis of data from GERDA, the MAJORANA DEMONSTRATOR, and LEGEND-200, characterized by a 90% confidence level exclusion sensitivity of 2.8 ×10 26 yr on the half-life of 0𝜈𝛽𝛽 decay, reveals no evidence for a signal and sets a new observed lower limit at 𝑇$^{0𝜈}_{1/2}$ > 1.9 × 10 26 yr (90% confidence level). Assuming the decay is mediated by Majorana neutrinos, this corresponds to an upper limit on the effective Majorana mass in the range 𝑚 𝛽𝛽 < 75–200 meV, depending on the adopted nuclear matrix element.
Simple models with both baryon and lepton number violation by two units
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Search for baryon and lepton number violating decay D ± → n ( n ¯ ) e ±
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Search for baryon and lepton number violating decays of Ξ 0 hyperons
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Constraints on lepton number violation with the 2 tonne · year CUORE dataset
Matter-antimatter asymmetry underlines the incompleteness of the current understanding of particle physics. Neutrinoless double-beta decay (0νββ) may help explain this asymmetry while unveiling the Majorana nature of the neutrino. The CUORE (Cryogenic Underground Observatory for Rare Events) experiment searches for 0νββ of 130 Te using a tonne-scale cryogenic calorimeter operated at milli-kelvin temperatures. We report no evidence of 0νββ and place a lower limit on the half-life of T 1/2 > 3.5 × 10 25 years (90% credibility interval) with over 2 tonne·years of TeO 2 exposure. Finally, the tools and techniques developed for this result and the 5-year stable operation of nearly 1000 detectors demonstrate crucial infrastructure for future-generation experiments capable of searching for 0νββ across multiple isotopes.
New Theories for Neutrino Masses and Dark Matter
The main goal of the project is to investigate new theories for neutrino masses and dark matter, and understand their testability in different experiments. The PI proposed several mechanisms for neutrino masses in the context of B-L theories, left-right symmetric theories, supersymmetric theories and grand unified theories. The PI would like to investigate new ways to understand the origin of neutrino masses where the seesaw scale is in the multi-TeV region. One can have a multi-TeV seesaw scale in scenarios where the same symmetry relevant for neutrino masses defines the dark matter relic density, or in the minimal supersymmetric theory based on local B-L. In these theories one can have new ways to understand the testability of the origin of neutrino masses at colliders and low energy experiments. In these theories one predicts the possibility to observe lepton number violating signatures at the LHC, one can predict large contributions to lepton number violating processes such as mu to e conversion, neutrinoless double beta decay experiments and others. The nature of the dark matter in the Universe is one of the most important problems in cosmology. Two of the most popular candidates are the Axions and the Weakly Interacting Massive Particles (WIMPs). The PI would like to investigate the implications of a new electroweak theta term similar to the QCD vacuum angle but in the SU(2) gauge sector of the SM which is physical if the baryon and lepton numbers are broken symmetries. We will investigate the implications of having a new electroweak theta term dark matter portal, the implications for baryogenesis and understand the constraints coming from different experiments such as the searches for electric dipole moments and axion experiments. The implications of having the electroweak theta term in theories with different sources of baryon and lepton number violation will be investigated. WIMPs are perhaps the most appealing candidates for many reasons. The PI would like to investigate the properties of WIMPs in different gauge theories, study the implications of the cosmological bounds on the WIMPs relic density for the symmetry breaking scale in models for new physics. The PI would like to investigate in great detail the predictions for gamma lines, neutrino lines and other striking signatures which can be present in these theories. These studies can have a profound impact in the testability of different theories for physics beyond the Standard Model.
Revisiting the connection of baryon number, lepton number, and operator dimension
The effects of heavy new particles beyond the Standard Model can be conveniently captured through higher-dimensional effective operators. As noted long ago by Weinberg, the amount of baryon and lepton number an operator can carry is intricately connected to its mass dimension. We derive an improved inequality for this connection and compare it to explicit operator constructions up to mass dimension 25. For the effective field theory of Standard Model plus right-handed neutrinos, our relationship is even an equality up to high mass dimension.