Constraining the strangeness content of the nucleon by measuring the ϕ meson mass shift in nuclear matter

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The behavior of the ϕ meson at finite density is studied, making use of a QCD sum rule approach in combination with the maximum entropy method. It is demonstrated that a possible mass shift of the ϕ in nuclear matter is strongly correlated to the strangeness content of the nucleon, which is proportional to the strange sigma term, σsN = mₛ N | ss | N. Our results furthermore show that, depending on the value of σsN, the ϕ meson could receive both a positive or negative mass shift at nuclear matter density. We find that these results depend only weakly on potential modifications of the width of the ϕ meson peak and on assumptions made on the behavior of four-quark condensates at finite density. To check the stability of our findings, we take into account several higher order corrections to the operator product expansion, including αₛ-corrections, terms of higher order in the strange quark mass and terms of higher twist that have not been considered in earlier works.