@article{6f8a9723cb9142febb671f6bc88e6301,
title = "Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN",
abstract = "We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e+e- pairs observed in the excited Be∗8 nucleus decays. Because of its coupling to electrons, the X could be produced in the bremsstrahlung reaction e-Z→e-ZX by a 100 GeV e- beam incident on an active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through the subsequent decay into a e+e- pair. With 5.4×1010 electrons on target, no evidence for such decays was found, allowing us to set first limits on the X-e- coupling in the range 1.3×10-4 ϵe4.2×10-4 excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A′) from nonobservation of the decay A′→e+e- of the bremsstrahlung A′ with a mass 23 MeV.",
author = "{(NA64 Collaboration)} and D. Banerjee and Burtsev, {V. E.} and Chumakov, {A. G.} and D. Cooke and P. Crivelli and E. Depero and Dermenev, {A. V.} and Donskov, {S. V.} and Dusaev, {R. R.} and T. Enik and N. Charitonidis and A. Feshchenko and Frolov, {V. N.} and A. Gardikiotis and Gerassimov, {S. G.} and Gninenko, {S. N.} and M. H{\"o}sgen and M. Jeckel and Karneyeu, {A. E.} and G. Kekelidze and B. Ketzer and Kirpichnikov, {D. V.} and Kirsanov, {M. M.} and Konorov, {I. V.} and Kovalenko, {S. G.} and Kramarenko, {V. A.} and Kravchuk, {L. V.} and Krasnikov, {N. V.} and Kuleshov, {S. V.} and Lyubovitskij, {V. E.} and V. Lysan and Matveev, {V. A.} and Mikhailov, {Yu V.} and Peshekhonov, {D. V.} and Polyakov, {V. A.} and B. Radics and R. Rojas and A. Rubbia and Samoylenko, {V. D.} and Tikhomirov, {V. O.} and Tlisov, {D. A.} and Toropin, {A. N.} and Trifonov, {A. Yu} and Vasilishin, {B. I.} and {Vasquez Arenas}, G. and Volkov, {P. V.} and V. Volkov and P. Ulloa",
year = "2018",
month = jun,
day = "8",
doi = "10.1103/PhysRevLett.120.231802",
language = "English",
volume = "120",
journal = "Physical Review Letters",
issn = "0031-9007",
publisher = "American Physical Society",
number = "23",
}