Phys.Rev. C 104, 044003 (2021)

A.J.Krasznahorkay, M.Csatlos, L.Csige, J.Gulyas, A.Krasznahorkay, B.M.Nyako, I.Rajta, J.Timar, I.Vajda, N.J.Sas

New anomaly observed in ⁴He supports the existence of the hypothetical X17 particle

NUCLEAR REACTIONS ³H(p, e⁺e^-)⁴He, E=510, 610, 900 keV; measured electron and positrons, energy-sum spectra and angular correlation of e⁺e^- pairs using scintillation detectors and double-sided silicon strip detectors (DSSD) at the 2-MV Tandetron accelerator of ATOMKI, Debrecen; deduced anomalous excess of e⁺e^- pairs around 115°, interpreted as creation and subsequent decay of a light particle during the direct capture process; extracted internal pair creation coefficient (IPCC), X17 boson branching ratio, mass of X17 particle with confidence level; likely the same as X17 particle suggested by 2016Kr01 (Phys. Rev. Lett. 116, 042501). ⁷Li(p, e⁺e^-)⁸Be, E=441 keV; measured angular correlation of e⁺e^- pairs for the 17.6-MeV, M1 transition in ⁸Be as a test of the experimental apparatus and methodology.

doi: 10.1103/PhysRevC.104.044003