LAUSR

One of the interesting portals linking a dark sector and the Standard Model (SM) is the kinetic mixing between the SM U(1)Y field with a new dark photon A′ from a U(1)A′ gauge interaction. Stringent limits have been obtained for the kinetic mixing parameter ???? through various processes. In this work, we study the possibility of searching for a dark photon interaction at a circular e+e− collider through the process e+e−→ γA′→ γμ+μ−. We find that the constraint on ????2 for dark photon mass in the few tens of GeV range, assuming that the μ+μ− invariant mass can be measured to an accuracy of 0.5% mA′, can be better than 3 × 10−6 for the proposed CEPC with a 10-year running at 3σ (statistic) level, and better than 2 × 10−6 for FCC-ee with even just one-year running at s = 240GeV, better than the LHCb, ATLAS, CMS experiments and other facilities can do in a similar dark photon mass range. For FCC-ee, running at s = 160GeV, the constraint can be even better.