@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",
note = "Funding Information: We gratefully acknowledge the support of the CERN management and staff and the technical staffs of the participating institutions for their vital contributions. We also thank Attila Krasznahorkay for useful discussions about the ATOMKI experiment, and Christophe Menezes Pires and Ondrej Subrt for their help. This work was supported by the HISKP, University of Bonn (Germany), JINR (Dubna), MON and RAS (Russia), SNSF Grant No. 169133 and ETHZ (Switzerland), and Grants FONDECYT No. 1140471 and No. 1150792, Ring ACT1406 and Basal FB0821 CONICYT (Chile). Part of the work on simulations was supported by the RSF Grant No. 14-12-01430.",
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",
}