Speaker
Description
The azimuthal angle difference between the decay planes of the two tau leptons in h to tau+ tau- probes charge-parity (CP) violation in the Higgs-tau Yukawa coupling. In the dominant hadronic channel tau+- to rho+- nu, the spin-analyzing power is suppressed by the mixture of longitudinal and transverse rho polarizations. We propose an energy-correlator (E4C) inspired method that weights each event by a power of the pion energy asymmetry in rho+- to pi+- pi0, preferentially selecting longitudinal rho mesons. Applied to e+ e- to Z to tau+ tau-, the weighting enhances the sensitivity of the visible-energy spectrum to the tau polarization P tau, and hence to the effective weak mixing angle sinthetaw. In a parton-level template-fit study of Z to tau+ tau- samples generated with MadGraph5 using a tau-decay UFO model, the single-sided weight reduces the statistical uncertainty on sinthetaw by 15 percent at the optimal exponent, equivalent to a 35 percent increase in integrated luminosity. Splitting the samples into forward and backward hemispheres yields a second, independent estimator whose combination improves the precision by a further factor of 1.4. These results establish E4C weighting as a simple and robust tool for precision tau physics at future lepton colliders.
