Probing anomalous $W^-W^+\gamma/Z$ couplings in the SMEFT with $e^-e^+ \to W^-W^+ \to 4j/\ell^-\ell^+\slashed{E}$ channel

TL;DR

This paper explores how dimension-6 operators in SMEFT affect anomalous W boson couplings at 250 GeV electron-positron colliders, using multi-channel analysis with advanced machine learning techniques to set limits on new physics effects.

Contribution

It introduces a comprehensive analysis combining multiple channels and machine learning methods to constrain anomalous W couplings within SMEFT at future colliders.

Findings

Fully hadronic channel provides strongest sensitivity to certain operators.

Semi-leptonic channel yields tighter limits on others.

Combined analysis with spin asymmetries improves constraints.

Abstract

We investigate anomalous charged triple gauge boson couplings induced by $SU(2)_L \times U(1)_Y$ gauge-invariant dimension-6 operators in the HISZ basis through the processes $e^-e^+ \to 4j$ and $e^-e^+ \to \ell^-\ell^+ + \text{missing energy}$ at $\sqrt{s}=250\,$GeV with longitudinally polarized beams. The analysis includes three CP-even operators $(O_{WWW}, O_W, O_B)$ and two CP-odd operators $(\tilde O_{WWW}, \tilde O_W)$, which parameterize deviations in the $W^-W^+\gamma/Z$ vertex. All leading-order contributions are included, including interference between $W^-W^+$ production and non-resonant amplitudes. In the $e^-e^+ \to 4j$ channel, $W^-W^+$ candidates are selected using boosted decision trees. The $W$-boson charges are reconstructed using a jet-charge observable, and jet flavors from $W$ decays are identified with a dedicated classifier, enabling measurements of vector polarization and correlation asymmetries. In the $e^-e^+ \to \ell^-\ell^+ + \text{missing energy}$ channel, events are selected with cuts on lepton transverse momentum and dilepton mass, and the two neutrino momenta are reconstructed using neural-network regression. Combining total cross sections with spin asymmetries allows constraints on anomalous gauge couplings. The fully hadronic channel provides the strongest sensitivity to $O_B$ and $\tilde O_W$, while the semi-leptonic channel yields tighter limits on $O_{WWW}$, $O_W$, and $\tilde O_{WWW}$. The fully leptonic channel adds complementary sensitivity. Finally, we derive marginalized limits on all five operators using a Markov Chain Monte Carlo analysis for several choices of systematic uncertainties and integrated luminosities.