Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays

Abstract

The 6.8$\sigma$ anomaly in excited 8Be nuclear decays via internal pair creation is fit well by a new particle interpretation. In a previous analysis, we showed that a 17 MeV protophobic gauge boson provides a particle physics explanation of the anomaly consistent with all existing constraints. Here we begin with a review of the physics of internal pair creation in 8Be decays and the characteristics of the observed anomaly. To develop its particle interpretation, we provide an effective operator analysis for excited 8Be decays to particles with a variety of spins and parities and show that these considerations exclude simple models with scalar particles. We discuss the required couplings for a gauge boson to give the observed signal, highlighting the significant dependence on the precise mass of the boson and isospin mixing and breaking effects. We present anomaly-free extensions of the Standard Model that contain protophobic gauge bosons with the desired couplings to explain the 8Be anomaly. In the first model, the new force carrier is a U(1)B gauge boson that kinetically mixes with the photon; in the second model, it is a U(1)(B-L) gauge boson with a similar kinetic mixing. In both cases, the models predict relatively large charged lepton couplings ~ 0.001 that can resolve the discrepancy in the muon anomalous magnetic moment and are amenable to many experimental probes. The models also contain vectorlike leptons at the weak scale that may be accessible to near future LHC searches.

35 pages + references, 6 figures; v2: generality of vector candidates discussion clarified, references added, published version

References in corpus (27)

• Secluded U(1) below the weak scale
• Test of the Equivalence Principle Using a Rotating Torsion Balance
• New Fixed-Target Experiments to Search for Dark Gauge Forces
• Search for a dark photon in e+e- collisions at BABAR
• Nucleon Electromagnetic Form Factors
• U-boson production in e+e- annihilations, psi and Upsilon decays, and Light Dark Matter
• Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at sqrt(s) = 8 TeV with the ATLAS detector
• Probing a Secluded U(1) at B-factories
• Searches for electroweak production of charginos, neutralinos, and sleptons decaying to leptons and W, Z, and Higgs bosons in pp collisions at 8 TeV
• Improved predictions for g-2 of the muon and α_{\rm QED}(M_Z^2)
• Discovering New Light States at Neutrino Experiments
• Unbroken B-L Symmetry
• Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays
• Fundamental Physics at the Intensity Frontier
• Compatibility of CAST search with axion-like interpretation of PVLAS results
• Neutrinophilic Non-Standard Interactions
• Search for new particles in events with one lepton and missing transverse momentum in $pp$ collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector
• Limits on Vectorlike Leptons from Searches for Anomalous Production of Multi-Lepton Events
• Theory for Baryon Number and Dark Matter at the LHC
• Projections for Dark Photon Searches at Mu3e
• Observation of Z decays to four leptons with the CMS detector at the LHC
• Measurement of the 4l Cross Section at the Z Resonance and Determination of the Branching Fraction of Z->4l in pp Collisions at sqrt(s) = 7 and 8 TeV with ATLAS
• Quantum Monte Carlo calculations of electromagnetic transitions in 8Be with meson-exchange currents derived from chiral effective field theory
• Searching for a new force at VEPP-3
• Dark matter, light mediators, and the neutrino floor
• The DarkLight Experiment: A Precision Search for New Physics at Low Energies
• Heavy Bino Dark Matter and Collider Signals in the MSSM with Vector-like 4th-Generation Particles

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• Dark Photons from Nuclear Transitions
• Displaced Searches for Light Vector Bosons at Belle II
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• New determination of proton spectroscopic factors and reduced widths for ${}^8$Be states in the $16.5-18.0$ MeV excitation energy region via the study of the ${}^7$Li(${}^3$He,d)${}^8$Be transfer reaction at E${}_{lab}$ $=20$ MeV
• Naturalness and a light $Z^{\prime }$
• Probing the ATOMKI X17 vector boson using Dalitz decays $V\to P{e}^{+}{e}^{-}$
• QED meson description of the anomalous particles at ~17 and ~38 MeV
• Possible Explanation of the Electron Positron Anomaly at 17 MeV in ${}^{8}Be$ Transitions Through a Light Pseudoscalar
• Puzzling behavior of hydrated YBCO
• CFNS Ad-Hoc meeting on Radiative Corrections Whitepaper
• ${}^8$Be Decay Anomaly and Light $Z^{\prime }$
• Flavor specific chiral $U(1{)}_X$ framework for explaining the ATOMKI anomaly
• The X17 with Chiral Couplings