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New anomaly observed in $^{12}$C supports the existence and the vector character of the hypothetical X17 boson
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abstract
Employing the $^{11}$B(p,$\gamma$)$^{12}$C nuclear reaction, the angular correlation of $e^+e^-$ pairs was investigated in the angular range of $40^\circ\Theta\leq 175^\circ$ for five different proton energies between E$_p$ = 1.50 - 2.50 MeV. At small angles ($\Theta\leq 120^\circ$), the results can be well interpreted by the internal pair creation process of electromagnetic radiations with E1 and M1 multipolarities and by the external pair creation in the target backing. However, at angles greater than $120^\circ$, additional count excess and anomalies were observed, which could be well accounted for by the existence of the previously suggested hypotetical X17 particle. Our results show that the X17 particle was generated mainly in E1 radiation. The derived mass of the particle is $m_\mathrm{X}c^2$=17.03$\pm 0.11 (stat) \pm 0.20 (syst)$ MeV. According to the mass, and to the derived branching ratio ($B_x=3.6(3)\times10^{-6}$), this is likely the same X17 particle, which we recently suggested for describing the anomaly observed in the decay of $^8$Be and $^4$He.
Forward citations
Cited by 7 Pith papers
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Possible Evidence for Neutral Color-Singlet $q\bar q$ Quark Matter from High-Energy Pb-Emulsion Collisions
The complex e+e- invariant mass spectrum below 50 MeV is attributed to thermal annihilation and bound states of QED-deconfined and confined neutral q bar q quark matter.
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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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The X17 with Chiral Couplings
A spin-1 X17 with chiral couplings fits the ATOMKI nuclear anomalies at 99% CL only in a parameter region that atomic parity violation and KLOE-2/NA64 exclude, driven mainly by the 12C(17.23) transition.
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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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