Can a protophobic vector boson explain the ATOMKI anomaly?

Abstract

In 2016, the ATOMKI collaboration announced [PRL {\bf 116}, 042501 (2016)] observing an unexpected enhancement of the $e^{+}-e^{-}$ pair production signal in one of the ${}^8$Be nuclear transitions induced by an incident proton beam on a ${}^7$Li target. Many beyond-standard-model physics explanations have subsequently been proposed. One popular theory is that the anomaly is caused by the creation of a protophobic vector boson ($X$) with a mass around 17 MeV [e.g., PRL\ {\bf 117}, 071803 (2016)] in the nuclear transition. We study this hypothesis by deriving an isospin relation between photon and $X$ couplings to nucleons. This allows us to find simple relations between protophobic $X$-production cross sections and those for measured photon production. The net result is that $X$ production is dominated by direct transitions induced by $E{1}^X$ and $L{1}^X$ (transverse and longitudinal electric dipoles) and $C{1}^X$ (charge dipole) without going through any nuclear resonance (i.e. Bremsstrahlung radiation) with a smooth energy dependence that occurs for all proton beam energies above threshold. This contradicts the experimental observations and invalidates the protophobic vector boson explanation.

8 pages, 4 figures, 1 table. Version close to the published: detailed discussions on multipoles and experimental signal (with a new figure) are included

References in corpus (11)

• Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
• Charge Symmetry Breaking and QCD
• The light U boson as the mediator of a new force, coupled to a combination of Q, B, L and dark matter
• Dynamical Evidence For a Fifth Force Explanation of the ATOMKI Nuclear Anomalies
• New evidence supporting the existence of the hypothetic X17 particle
• Quantum Monte Carlo calculations of electromagnetic transitions in 8Be with meson-exchange currents derived from chiral effective field theory
• Protophobic Light Vector Boson as a Mediator to the Dark Sector
• Atomki Anomaly in Family-Dependent $U(1{)}^{\prime }$ Extension of the Standard Model
• The new interaction suggested by the anomalous ${}^8$Be transition sets a rigorous constraint on the mass range of dark matter
• Is There a Sign of New Physics in Beryllium Transitions?
• The muon (g - 2) anomaly and a new light vector boson

Cited by in corpus (22)

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• The X17 boson and the ${}^3$H$(p,e^{+}{e}^{-}{)}^4$He and ${}^3$He$(n,e^{+}{e}^{-}{)}^4$He processes: a theoretical analysis
• Resonant search for the X17 boson at PADME
• The $U$ boson, interpolating between a generalized dark photon or dark $Z$, an axial boson and an axionlike particle
• An updated view on the ATOMKI nuclear anomalies
• Neutrino Constraints and the ATOMKI X17 Anomaly
• Explaining Atomki anomaly and muon $g-2$ in $U(1{)}_X$ extended flavour violating two Higgs doublet model
• Checking the ${}^8$Be anomaly with a two-arm electron positron pair spectrometer
• Status of the X17 search in Montreal
• The Angular Correlations in the $e^{+}{e}^{-}$ Decay of Excited States in 8Be
• On the Atomki nuclear anomaly after the MEG-II result
• Tests of the Atomki anomaly in lepton pair decays of heavy mesons
• Ab initio investigation of the ${}^7$Li($p,e^{+}{e}^{-}$)${}^8$Be process and the X17 boson
• X17 discovery potential in the $\gamma N\to e^{+}{e}^{-}N$ process at electron scattering facilities
• Hunting for a 17 MeV particle coupled to electrons
• ARIEL experiments and theory
• Probing the ATOMKI X17 vector boson using Dalitz decays $V\to P{e}^{+}{e}^{-}$
• Novel approach to investigate ATOMKI anomaly using Coherent CAPTAIN-Mills detectors
• A Direct Detection Search for Hidden Sector New Particles in the 3-60 MeV Mass Range
• Radiative and Dalitz decays of ${\rm Y}(1S)$ in the light of the ATOMKI X17 anomaly