Determination of the ϕ-meson production process and its absorption cross section via directed flow

Abstract

It is shown that the directed flow of $\varphi$-mesons in Au+Au collisions at $\sqrt{s_{NN}}=3$ GeV, is sensitive to the production and the absorption cross section of the $\varphi$ in a nuclear medium. This provides a new observable to constrain the in-medium properties of the $\varphi$ which is independent of its absolute production rate. STAR data disfavor any significant $\varphi$-N absorption in dense nuclear matter and are consistent with a very small cross section of the $\varphi$ comparable to the vacuum cross section. The similarity of the $\varphi$-meson and proton directed flow also indicates that the $\varphi$ is produced in conjunction with a baryon.