Upgrade of the $\beta\!-\!\nu$ correlation experiment with beta decay of optically trapped $\rm^{38m}$K atoms*

TRIUMF's $\beta\!-\!\nu$ correlation measurements from beta decay of optically trapped $\rm^{38m}$K atoms resulted in the world best limit on the presence of general scalar interaction in superallowed $0^+\!\rightarrow 0^+$ Fermi decays (PRL {\bf 94},142501,2005). Observing trapped atoms by $\Delta E-E$ scintillator based beta-telescope and MCP based recoil detector in back-to-back geometry, we were able to deduce $\beta\!-\!\nu$ correlations. Analysis of the systematics has shown that the main limitations come from characterisation of the beta-detector, applied electric field and knowlege of energy dependent probability of the recoil ionization. A new improved setup utilyzing larger experimental chamber and detectors and stronger, better characterized applied electric field should allow us to significantly reduce systematic errors and reach 0.1\% resulting error.