Dark photon search in the mass range between 1.5 and 3.4 GeV/c2

Abstract

Using a data set of 2.93 fb −1 taken at a center-of-mass energy sqrt(s)=3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions e+e−→e+e−γISR and e+e−→μ+μ−γISR for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/ c 2 and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range

X(16.7) production in electron–positron collision

“…A significant enhancement relative to the internal pair creation was observed at large angles in the invariant-mass distribution of electron-positron pairs production. However, no anomaly is seen in the isovector 8 Be * → 8 Be transition. This observation is hard to be understood within the regime of conventional theory, but could be attributed to a neutral isoscalar particle X with the mass of 16.7 MeV and the saturating decay X → e + e − beyond SM.…”

“…At BESIII detector, the 1.5-3. 4 GeV mass range was explored and limits on the U−γ mixing strength were also set [8]. Similarly in the KLOE-2 experiment, they searched for the dark photon in both e + e − → Uγ [9] and φ → Uη processes [10].…”

“…In 2016, an extraordinary experimental phenomenon was observed in the isoscalar 8 Be nuclear transition, 8 Be * → 8 Be [22], and new measurements are presented three times recently [23][24][25]. A significant enhancement relative to the internal pair creation was observed at large angles in the invariant-mass distribution of electron-positron pairs production.…”

“…In Ref. [30], the production of a hidden vector boson with axial-vector couplings to leptons and light quarks in the isoscalar 8 Be * → 8 Be nuclear transition is investigated. Note, along with the axialvector couplings to the Standard Model fermions, we need to devote some effort to obtain a UV-complete anomaly-free theory [36,37].…”

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AbstractThe anomaly found in the excited 8 Be nuclear transition to its ground state is attributed to a spin-1 gauge boson X (16.7). To hunt for this boson, we propose two traps: e + e − → X γ and J/ψ → X γ , both following with X → e + e − decay.

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