Tau $g-2$ at $e^-e^+$ colliders with momentum dependent form factor

Abstract

The deviation between the prediction based on the standard model and the measurement of the muon g−2 is currently at 3−4σ (can be up to 7σ in the upcoming E989 experiment). If this discrepancy is attributable to new physics, it is expected that the new contributions to the tau g−2 even larger than those of muon due to its large mass. However, it is much more difficult to directly measure the tau g−2 because of its short lifetime. In this report, we consider the effect of the tau g−2 at e − e + colliders using a model independent approach. Using the tau pair production channel at the Large Electron Position Collider (LEP), we have determined the allowed range for the new physics contribution of the tau g−2 assuming a q 2 -dependence ansatz for the magnetic form factor. In our analysis, we consider the standard model one-loop correction as well as the initial state photon radiation. We also investigated the prospect at future e − e + colliders, and determined the expected allowed range for the new physics contribution to the tau g−2. Given the proposed beam polarization configuration at the International Linear Collider (ILC), we have analyzed the dependence of this allowed range on the integrated luminosity, as well as the relative systematic error.