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Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN
Journal
Physical Review Letters
Date Issued
2018-06-08
Author(s)
Banerjee, D.
Burtsev, V. E.
Chumakov, A. G.
Cooke, D.
Crivelli, P.
Depero, E.
Dermenev, A. V.
Donskov, S. V.
Dusaev, R. R.
Enik, T.
Charitonidis, N.
Feshchenko, A.
Frolov, V. N.
Gardikiotis, A.
Gerassimov, S. G.
Gninenko, S. N.
Hösgen, M.
Jeckel, M.
Karneyeu, A. E.
Kekelidze, G.
Ketzer, B.
Kirpichnikov, D. V.
Kirsanov, M. M.
Konorov, I. V.
Kramarenko, V. A.
Kravchuk, L. V.
Krasnikov, N. V.
Lysan, V.
Matveev, V. A.
Mikhailov, Yu V.
Peshekhonov, D. V.
Polyakov, V. A.
Radics, B.
Rojas, R.
Rubbia, A.
Samoylenko, V. D.
Tikhomirov, V. O.
Tlisov, D. A.
Toropin, A. N.
Trifonov, A. Yu
Vasilishin, B. I.
Vasquez Arenas, G.
Volkov, P. V.
Volkov, V.
Ulloa, P.
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 eþe− pairs observed in the excited 8
Be 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 eþe− 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 ≲ ϵe ≲
4.2 × 10−4 excluding part of the allowed parameter space. We also set new bounds on the mixing strength
of photons with dark photons (A0
) from nonobservation of the decay A0 → eþe− of the bremsstrahlung A0
with a mass ≲23 MeV
anomalous excess of eþe− pairs observed in the excited 8
Be 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 eþe− 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 ≲ ϵe ≲
4.2 × 10−4 excluding part of the allowed parameter space. We also set new bounds on the mixing strength
of photons with dark photons (A0
) from nonobservation of the decay A0 → eþe− of the bremsstrahlung A0
with a mass ≲23 MeV
Subjects
