Search for Z ′ → μ + μ − in the L μ − L τ gauge-symmetric model at Belle

Abstract

We search for a new gauge boson Z ′ that couples only to heavy leptons and their corresponding neutrinos in the process e + e − → Z ′ ( → μ + μ − ) μ + μ − , using a 643

fb − 1 data sample collected by the Belle experiment at or near the Υ ( 1 S , 2 S , 3 S , 4 S , 5 S ) resonances at the KEKB collider. While previous searches for Z ′ performed a data-based estimation of the initial state radiation effect, our search for the Z ′ is the first to include effects due to initial state radiation in the signal simulated samples that were used in estimating the detection efficiency. No signal is observed in the Z ′ mass range of 0.212 – 10

GeV / c 2 , and we set an upper limit on the coupling strength, g ′ , constraining the possible Z ′ contribution to the anomalous magnetic dipole moment of the muon.