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{-}4 sigma . 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-square-dependence ansatz for the magnetic form factor. We also investigated the prospect at future e^+e^- colliders, such as International Linear Collider, the Compact Linear Collider, the Future Circular e^+e^- Collider, and Circular Electron Positron Collider, and determined the expected allowed range for the new physics contribution to the tau anomalous magnetic moment. The best limits are about 4{-}5 times more severe than the LEP one due to the beam polarization and the high luminosities at future colliders.