Strategy to measure tau g−2 via photon fusion in LHC proton collisions

Measuring the tau-lepton (τ) anomalous magnetic moment aτ=(gτ−2)/2 in photon fusion production (γγ→ττ) tests foundational Standard Model principles. However, γγ→ττ eludes observation in LHC proton collisions (pp) despite enhanced new physics sensitivity from higher-mass reach than existing probes. We propose a strategy to measure pp→p(γγ→ττ)p by introducing the overlooked electron-muon signature with vertex isolation for signal extraction. Applying the effective field theory of dipole moments, we estimate 95% confidence level sensitivity of −0.0092<aτ<0.011 assuming 300  fb−1 luminosity and 5% systematics. This fourfold improvement beyond existing constraints opens a crucial path to unveiling new physics imprinted in tau-lepton dipoles.