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We apply the optimized perturbation theory (OPT) to resum the perturbativeseries describing the mass gap of the bidimensional $\phi^4$ theory in the$\mathbb{Z}_2$ symmetric phase. Already at NLO (one loop) the method is capableof generating a quite reasonable non-perturbative result for the criticalcoupling. At order-$g^7$ we obtain $g_c = 2.779(25)$ which compares very wellwith the state of the art ${\rm N}^8{\rm LO}$ result, $g_c = 2.807(34)$. As anovelty we investigate the supercritical region showing that it contains someuseful complimentary information that can be used in extrapolations toarbitrarily high orders.

Critical behavior of the 2d scalar theory: resumming the ${\rm N}^8{\rm LO}$ perturbative mass gap