Model-independent study on the anomalous ττ¯γ couplings at the ILC

The potential of the process γγ→ττ¯γ is examined in a model-independent way using the effective Lagrangian approach for the International Linear Collider, a proposed electron-positron machine which is designed with standard configurations of 0.25 TeV/2000 fb−1, 0.35 TeV/200 fb−1 and 0.5 TeV/4000 fb−1. The limits obtained for the tau lepton's anomalous magnetic dipole moment a˜τ and the tau lepton's anomalous electric dipole moment d˜τ defining the anomalous ττ¯γ couplings at 95% confidence level and systematic uncertainties of δsys=0,5,10% are compared with the experimental results. The best limits obtained with δsys=0% on the anomalous couplings are −0.00082<a˜τ<0.00050 and |dτ˜|<3.59×10−18 ecm, respectively. Also, the limits on the anomalous couplings do not improve proportionately to the luminosity due to the systematic error considered here. The reason of this situation is the systematic error which is much bigger than the statistical error. If the systematic error is improved, we expect better limits on the couplings. However, the best limits on the anomalous couplings for the process γγ→ττ¯γ with s=500 GeV, Lint=4000 fb−1 and δsys=0% can be improved up to 4 times for a˜τ and 9 times for d˜τ according to case with δsys=10%. Our results show that γγ collisions at the ILC give results up to one order of magnitude for a˜τ and two orders of magnitude for d˜τ better than the current experimental limits.

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