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A new anomaly observed in $^4$He supports the existence of the hypothetical X17 particle
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abstract
Energy-sum and angular correlation spectra of $e^+e^-$ pairs produced in the $^{3}$H(p,$\gamma$)$^{4}$He nuclear reaction have been studied at $E_p$=510, 610 and 900 keV proton energies. The main features of the spectra can be understood by taking into account the internal and external pair creations following the direct proton radiative capture by $^{3}$H. However, these processes cannot account for the observed peak around 115$^\circ$ in the angular correlation spectra. This anomalous excess of $e^+e^-$ pairs can be described by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle is $m_\mathrm{X}c^2$=16.94$\pm0.12 (stat) \pm 0.21 (syst)$~MeV. According to the mass and branching ratio ($B_x=5.1(13)\times10^{-6}$), this is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)] for describing the anomaly observed in the decay of $^8$Be.
Forward citations
Cited by 5 Pith papers
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Updated E141 constraints on a long-lived $X_{17}$ vector boson
A refined simulation of SLAC E141 shows the experiment's old exclusion region does not cover the 16.9 MeV X17, leaving a window at ε_e between 6.5e-5 and 1.1e-4.
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Flavor specific chiral $U(1)_X$ framework for explaining the ATOMKI anomaly
A gauged, flavor-specific U(1)_X two-Higgs-doublet model can realize the axial-vector Z' couplings needed to explain the ATOMKI 8Be and 4He anomalies while evading current bounds.
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Probing the ATOMKI X17 vector boson using Dalitz decays $V\to Pe^+e^-$
In a quark-model calculation, X17 contributions to D*, B*, and J/psi Dalitz decays are too small to explain the BESIII D*0 e+e- excess unless quark couplings are far outside ATOMKI-favored ranges.
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Potential for the discovery of the protophobic boson at the STCF
Detector-level simulations indicate the proposed STCF drift chamber could discover the 17 MeV protophobic X17 boson through displaced electron-positron vertices if Standard Model backgrounds stay below about 10^4 even...
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Where to find $X(17)$?
Combining existing bounds with a new parity-violating Møller asymmetry constraint, the paper's body claims no surviving parameter space for scalar, pseudoscalar, vector, axial-vector, or V±A X(17)-electron couplings.
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