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Sigma meson in QCD sum rules using a two quark current with derivatives

We study the $σ$ meson in QCD sum rules using a two quark interpolating field with derivatives. In the constituent quark model, the $σ$ meson is composed of a quark and an antiquark in the relative p-wave state and is thus expected to have a larger overlap with an interpolating field that measures the derivative of the relative quark wave-function. While the sum rule with a current without derivatives gives a pole mass of around 1 GeV, the present sum rule with a derivative current gives a mass of around 550 MeV and a width of 400 MeV, that could be identified with the $σ$ meson.