Millicharged particles at electron colliders

Abstract

We propose to search for millicharged particles in electron colliders operated with the center-of-mass energies at Oð1-10Þ GeV, which include Belle II, BESIII, BABAR, and also the proposed experiment Super Tau Charm Factory (STCF). We use the monophoton final state at electron colliders to probe the parameter space of millicharged particles, that is spanned by millicharge ϵ and mass m. We find that electron colliders have sensitivity to the previously unexplored parameter space for millicharged particles with MeV-GeV mass: ϵ ≲ Oð10 −1 Þ for 0.5 GeV ≲ m ≲ 3.5 GeV in BABAR, ϵ ≲ Oð10 −3 Þ for 0.1 GeV ≲ m ≲ 1.5 GeV in BESIII, ϵ ≲ 10 −3 − 10 −2 for 0.1 GeV ≲ m ≲ 4 GeV in Belle II, and ϵ ≲ Oð10 −4 Þ for 1 MeV ≲ m ≲ 1 GeV in STCF.

Muon g − 2 from millicharged hidden confining sector

“…Other low-energy lepton colliders such as BaBar [24], BESIII [25] and Belle II could have impressive projected limits of N χ ε 2 10 −6 for m χ < 1 GeV if there is no additional larger backgrounds as considered in ref. [26]. Additionally, searches for events with large missing energy in the fixed-target experiment with an electron beam can also be used to constrain the millicharged particles, if one recasts the limits on produced on-shell invisible dark photon into the signals with two mCPs in the NA64 experiment [27,28].…”

Constraining nonstandard neutrino interactions at electron colliders

“…For the Belle II detector, which is asymmetric, the maximum energy of the monophoton events in the bBG in the CM frame, E m γ , is given by [54,55] (if not exceeding…”

“…By integrating the differential cross section in Eq. ( 10) in the phase space regions under these two different detector cuts, and assuming photon detection efficiency as 95% [53], with 50 ab −1 integrated luminosity about 2280 (15230) irreducible BG events with the "low-mass cut" ("high-mass cut") can be reached at Belle II [54]. For the reducible background, it is found that about 300 (25000) gBG events survived the "lowmass cut" ("high-mass cut") with 20 fb −1 integrated luminosity [53].…”

Characterizing Dark Matter Signals with Missing Momentum Experiments

“…Thus, it is essential to have a complementary array of experiments that can probe these interactions at different √ s. For example, it is clear from Fig. 6 that a MM experiment with a few signal events will not be able to distinguish between the production of an on-shell mediator with the photon energy spectrum if the mediator is massive and m A < √ s, or a broader excess if the mediator is massless [3,[54][55][56][57].…”