Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^+e^-$ pairs
Abstract
The improved results on a direct search for a new X(16.7 MeV) boson which could explain the anomalous excess of pairs observed in the excited 8Be nucleus decays ("Berillium anomaly") are reported. Due to its coupling to electrons, the X boson could be produced in the bremsstrahlung reaction e-Z -> e-ZX by a high-energy beam of electrons incident on active target in the NA64 experiment at the CERN SPS and observed through its subsequent decay into pair. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4\times 10^{10} electrons on target collected in 2017 and 2018. This allows to set the new limits on the -- coupling in the range 1.2 \times 10^{-4} < \epsilon_e < 6.8 \times 10^{-4}, excluding part of the parameter space favored by the Berillium anomaly. We also set new bounds on the mixing strength of photons with dark photons (A') from non-observation of the decay of the bremsstrahlung A' with a mass below 24 MeV.
Keywords
Cite
@article{arxiv.1912.11389,
title = {Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^+e^-$ pairs},
author = {D. Banerjee and J. Bernhard and V. E. Burtsev and A. G. Chumakov and D. Cooke and P. Crivelli and E. Depero and A. V. Dermenev and S. V. Donskov and R. R. Dusaev and T. Enik and N. Charitonidis and A. Feshchenko and V. N. Frolov and A. Gardikiotis and S. G. Gerassimov and S. N. Gninenko and M. Hoesgen and M. Jeckel and V. A. Kachanov and A. E. Karneyeu and G. Kekelidze and B. Ketzer and D. V. Kirpichnikov and M. M. Kirsanov and V. N. Kolosov and I. V. Konorov and S. G. Kovalenko and V. A. Kramarenko and L. V. Kravchuk and N. V. Krasnikov and S. V. Kuleshov and V. E. Lyubovitskij and V. Lysan and V. A. Matveev and Yu. V. Mikhailov and L. Molina Bueno and D. V. Peshekhonov and V. A. Polyakov and B. Radics and R. Rojas and A. Rubbia and V. D. Samoylenko and D. Shchukin and V. O. Tikhomirov and I. Tlisova and D. A. Tlisov and A. N. Toropin and A. Yu. Trifonov and B. I. Vasilishin and G. Vasquez Arenas and P. V. Volkov and V. Yu. Volkov and P. Ulloa},
journal= {arXiv preprint arXiv:1912.11389},
year = {2020}
}
Comments
7 pages, 5 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:1803.07748