Search for the dark photon in <i>B</i><SUP>0</SUP> → <i>A</i>′<i>A</i>′, <i>A</i>′ → <i>e</i><SUP>+</SUP><i>e<SUP>-</SUP></i>, <i>μ</i><SUP>+</SUP><i>μ<SUP>-</SUP></i>, and <i>π</i><SUP>+</SUP><i>π<SUP>-</SUP></i> decays at Belle

Abstract

We present a search for the dark photon A in the B-0 -> A ' A ' decays, where A ' subsequently decays to e(+)e(-), mu(+)mu(-), and pi(+)pi(-). The search is performed by analyzing 772 x 10(6) B (B) over bar events collected by the Belle detector at the KEKB e(+)e(-) energy-asymmetric collider at the Upsilon(4S) resonance. No signal is found in the dark photon mass range 0.01 GeV/c(2) <= m(A ') <= 2.62 GeV/c(2), and we set upper limits of the branching fraction of B-0 -> A ' A ' at the 90% confidence level. The products of branching fractions, B(B-0 -> A ' A ) x B(A '-> e(+)e(-))(2) and B(B-0 -> A ' A ') x B(A '-> mu(+)mu(-))(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(B-0 -> 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) at m(h ') similar or equal to m(B0) +/- 40 MeV/c(2) and 10(-1)-1 at mh ' similar or equal to m(B0) +/- 3 GeV/c(2).