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

TL;DR

This paper calculates the next-to-leading order electroweak corrections to tau pair production via photon fusion in lead-lead ultraperipheral collisions, revealing a small but significant impact on cross sections and distributions relevant for tau anomalous magnetic moment studies.

Contribution

It provides the first detailed analysis of NLO electroweak corrections to gamma gamma to tau+ tau- in Pb-Pb UPC, including their effect on cross sections and distributions.

Findings

EW correction reduces total cross section by about 3% at 5.02 TeV.

Weak correction is approximately four times larger than QED correction.

Differential distributions show different lineshapes with NLO corrections.

Abstract

We study the next-to-leading order (NLO) electroweak (EW) corrections to the $\gamma \gamma \to \tau^+ \tau^-$ process in Pb-Pb ultraperipheral collision (UPC). We find that the EW correction $\delta \sigma_{\mathrm{EW}}$ decreases the total cross section $\sigma_{\mathrm{NLO}} = \sigma_{\mathrm{LO}} + \delta \sigma_{\mathrm{EW}}$ by -3\% at Pb-Pb center-of-mass energy $\sqrt{s_{NN}}=5.02$ TeV. The weak correction plays significant role whose contribution is about -4 times of that of QED. The CMS and ATLAS collaborations use the reaction $\gamma\gamma \to \tau^+ \tau^-$ in Pb-Pb and proton-proton UPC to constrain tau's anomalous magnetic moment $a_\tau$. By parameterizing the $\gamma \tau \tau$ vertex with two form factors $F_{1,2}$, the cross section can be written as $\sigma_{a_\tau} = \sigma_{\mathrm{LO}} + \delta \sigma_{a_\tau}$, where $\delta \sigma_{a_\tau}$ is proportional to $a_\tau$. The impact of NLO EW corrections on $a_\tau$ bounds in Pb-Pb UPC is limited, as the current experimental bounds are loose. We also find that various differential distributions of the two ratios $\mathrm{d} \sigma_{\mathrm{NLO}}/ \mathrm{d} \sigma_{\mathrm{LO}}$ and $\mathrm{d} \sigma_{a_\tau}/ \mathrm{d} \sigma_{\mathrm{LO}}$ have different lineshapes. This work is significant to precisely study the interaction of $\gamma \tau \tau$ via $\gamma \gamma \to \tau^+ \tau^-$ process.