Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN

(NA64 Collaboration)

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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.

Original languageEnglish
Article number231802
JournalPhysical Review Letters
Volume120
Issue number23
DOIs
Publication statusPublished - 8 Jun 2018

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ASJC Scopus subject areas

  • Physics and Astronomy(all)

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