Search for the dark photon in B0→A′A′, A′→e+e−, μ+μ−, and π+π− decays at Belle

Journal of High Energy Physics. 2021. Vol. 2021. No. 4. Article 191.

Park S. -., Aushev T., Mizuk R., Pakhlova G., Popov V., Uglov T., Zhulanov V.

We present a search for the dark photon A′ in the B0 → A′A′ decays, where A′ subsequently decays to e+e−, μ+μ−, and π+π−. The search is performed by analyzing 772 × 106 BB events collected by the Belle detector at the KEKB e+e− energy- asymmetric collider at the Υ(4S) resonance. No signal is found in the dark photon mass range0.01GeV/c2≤mA′ ≤2.62GeV/c2,andwesetupperlimitsofthebranchingfraction of B0 → A′A′ at the 90% confidence level. The products of branching fractions, B(B0 → A′A′) × B(A′ → e+e−)2 and B(B0 → A′A′) × B(A′ → μ+μ−)2, have limits of the order of 10−8 depending on the A′ mass. Furthermore, considering A′ decay rate to each pair of charged particles, the upper limits of B(B0 → A′A′) are of the order of 10−8–10−5. From the upper limits of B(B0 → A′A′), we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10−2–10−1 atmh′ ≃mB0 ±40MeV/c2 and10−1–1atmh′ ≃mB0 ±3GeV/c2.

Keywords: Beyond Standard Model, B physics, Branching fraction, Standart model

Publication based on the results of: Investigation of the nature of the bottomonium states on the data of the Belle experiment and development of new research methods in charm and tau-lepton physics in experiments on electron-positron colliders (2021)