NLO EW corrections to tau pair production via photon fusion in Pb-Pb ultraperipheral collisions

Abstract

We study the next-to-leading order (NLO) electroweak (EW) corrections to the γγ→τ+τ− process in a Pb-Pb ultraperipheral collision (UPC). We find that the EW correction δσEW decreases the total cross section σNLO=σLO+δσEW by −3% at Pb-Pb center-of-mass energy sNN=5.02 TeV. The weak correction plays a significant role whose contribution is about–4 times that of QED. The CMS and ATLAS Collaborations use the reaction γγ→τ+τ− in Pb-Pb and proton-proton UPCs to constrain tau’s anomalous magnetic moment aτ. By parametrizing the γττ vertex with two form factors F1,2, the cross section can be written as σaτ=σLO+δσaτ, where δσaτ is proportional to aτ. The impact of NLO EW corrections on aτ bounds in a Pb-Pb UPC is limited, as the current experimental bounds are loose. We also find that various differential distributions of the two ratios dσNLO/dσLO and dσaτ/dσLO have different line shapes. This work is significant to precisely study the interaction of γττ via the γγ→τ+τ− process. Published by the American Physical Society 2025