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.
Highlights
IntroductionThe X17 boson is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be +X17, and decays through the X17 → e+e− process
We measured electron-positron angular correlations for the 17.6 MeV and 18.15 MeV, J p = 1+ → Jπ = 0+, M1 transitions in 8Be and an anomalous angular correlation was observed [1]
The contribution coming from the external pair creation (EPC) of the 17.6 MeV γ rays is shown by a FIG. 4. e+e− angular correlations obtained for the 17.6 MeV transition of 8Be by using thin target backing
Summary
The X17 boson is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be +X17, and decays through the X17 → e+e− process Constraints on such a new particle, were taken into account by Feng and co-workers [11,12,13]. The background in the spectrum below E (sum) = 17 MeV is created by external pairs induced by the γ rays coming from the direct proton capture on the 3H target. The angular correlations of the e+e− pairs for the background region marked in Fig. 6 are shown in Fig. 8, to Fig. 7
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
