Study of anomalous $$W^-W^+\gamma /Z$$ couplings using polarizations and spin correlations in $$e^-e^+\rightarrow W^-W^+$$ with polarized beams

Abstract

AbstractWe investigate the anomalous $$W^-W^+\gamma /Z$$ W - W + γ / Z couplings in $$e^-e^+\rightarrow W^-W^+$$ e - e + → W - W + followed by semileptonic decay using a complete set of polarization and spin correlation observables of W boson with the longitudinally polarized beam. We consider a complete set of dimension-six operators affecting $$W^-W^+\gamma /Z$$ W - W + γ / Z vertex, which are $$SU(2)\times U(1)$$ S U ( 2 ) × U ( 1 ) gauge invariant. Some of the polarization and spin correlation asymmetries average out if the daughter of $$W^+$$ W + is not tagged and to overcome this we developed an artificial neural network and boosted decision trees to distinguish down-type jets from up-type jets. We obtain bounds on the anomalous couplings using MCMC analysis at $$\sqrt{s} = 250$$ s = 250 GeV with integrated luminosities of $$\mathcal {L}\in \{100~\text {fb}^{-1}, 250~\text {fb}^{-1}, 1000~\text {fb}^{-1}, 3000~\text {fb}^{-1}\}$$ L ∈ { 100 fb - 1 , 250 fb - 1 , 1000 fb - 1 , 3000 fb - 1 } and different sets of systematic errors. We find that using spin-related observables along with cross section in the presence of initial beam polarization significantly improves the bounds on anomalous couplings compared to previous studies.