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Search for charge non-conservation and Pauli exclusion principle violation with the Majorana Demonstrator


Charge conservation and the Pauli exclusion principle result from fundamental symmetries in the standard model of particle physics, and are typically taken as axiomatic. High-precision tests for small violations of these symmetries could point to new physics. Here we consider three models for violation of these processes, which would produce detectable ionization in the high-purity germanium detectors of the Majorana Demonstrator experiment. Using a 37.5 kg yr exposure, we report a lower limit on the electron mean lifetime, improving the previous best limit for the \(e\to {\nu }_{e}\overline{{\nu }_{e}}{\nu }_{e}\) decay channel by more than an order of magnitude. We also present searches for two types of violation of the Pauli exclusion principle, setting limits on the probability of an electron to be found in a symmetric quantum state.

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Fig. 1: Three processes disallowed by quantum mechanics that would produce ionization in Ge atoms.
Fig. 2: A charge non-conserving decay \({\boldsymbol{e}}\to {\mathbf{\nu}}_{\boldsymbol{e}}{\overline{\mathbf{\nu}}}_{\boldsymbol{e}}{\mathbf{\nu}}_{\boldsymbol{e}}\) from a Ge K-shell electron would produce a peak at 11.1 keV.
Fig. 3: The combined 228Th calibration spectrum from all active detectors in the Majorana Demonstrator.
Fig. 4: Searching for a violation of the Pauli exclusion principle via detection of an ‘echo’ peak.
Fig. 5: A PEP-violating transition of an L-shell electron to the fully occupied K shell in Ge would produce a peak at 10.6 keV.

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This material is based upon work supported by the US Department of Energy, Office of Science, Office of Nuclear Physics under contract/award numbers DE-AC02-05CH11231, DE-AC05-00OR22725, DE-AC05-76RL0130, DE-FG02-97ER41020, DE-FG02-97ER41033, DE-FG02-97ER41041, DE-SC0012612, DE-SC0014445, DE-SC0018060, DE-SC0022339 and LANLEM77/LANLEM78. We acknowledge support from the Particle Astrophysics Program and Nuclear Physics Program of the National Science Foundation through grant numbers MRI-0923142, PHY-1003399, PHY-1102292, PHY-1206314, PHY-1614611, PHY-1812409, PHY-1812356, PHY-2111140 and PHY-2209530. We gratefully acknowledge the support of the Laboratory Directed Research & Development (LDRD) programme at Lawrence Berkeley National Laboratory for this work. We gratefully acknowledge the support of the US Department of Energy through the Los Alamos National Laboratory LDRD Program, the Oak Ridge National Laboratory LDRD Program and the Pacific Northwest National Laboratory LDRD Program for this work. We gratefully acknowledge the support of the South Dakota Board of Regents Competitive Research Grant. We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada, funding reference number SAPIN-2017-00023, and from the Canada Foundation for Innovation John R. Evans Leaders Fund. We acknowledge support from the 2020/2021 L’Oréal-UNESCO for Women in Science Programme. This research used resources provided by the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory and by the National Energy Research Scientific Computing Center, a US Department of Energy Office of Science User Facility. We thank our hosts and colleagues at the Sanford Underground Research Facility for their support.

Author information

Authors and Affiliations



All authors were involved in various aspects of detector construction, operation, maintenance, data acquisition, data-taking shifts, software development, data processing and analysis. C.W. and I.K. developed the low-energy data cleaning, and low-energy statistical analysis and spectrum fit techniques. J.M.L.-C. and C.W. conducted the high-energy spectral analysis and derived the limit on the Type I PEP-violating process. I.K. derived limits for the electron lifetime and Type III PEP-violating process. C.W. and I.K. wrote the paper. All authors reviewed, commented and approved the results and the final version of the paper.

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Correspondence to I. Kim or C. Wiseman.

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Nature Physics thanks Miriam Diamond, Ziqing Hong, Rabindra Mohapatra and Alessio Porcelli for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Profiles of the likelihood function over the branching ratio B = β2/2, defined as the ratio of lifetimes between PEP-obeying and PEP-violating atomic transitions of electrons.

DEP: β2/2 ≤ 3.22e−04 (90% CL). SEP: β2/2 ≤ 9.99e−04 (90%). Combined: β2/2 ≤ 3.69e − 04 (90%). The profiles from the single-escape peak region (dotted) and the double-escape peak region (dot-dashed) are added and shifted to produce the combined curve (solid black). The upper limits are computed at the intersection Δχ2 = 2.71, representing the 90% confidence level. Vertical lines representing the 90% upper limits are added for reference.

Extended Data Table 1 Best-fit parameters for the germanium peak shape function in the single-escape peak (SEP) and double-escape peak (DEP) regions

Source data

Source Data Fig. 2

Histogram data points with brief description in header.

Source Data Fig. 3

Histogram data points with brief description in header.

Source Data Fig. 4

One file includes data for the top and bottom plots. Histogram data points with brief description in header.

Source Data Fig. 5

Histogram data points with brief description in header.

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The MAJORANA Collaboration. Search for charge non-conservation and Pauli exclusion principle violation with the Majorana Demonstrator. Nat. Phys. (2024).

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