Strangeness suppression, the $ϕ$ meson and $Λ\barΛ$ spin correlations from exact strangeness conservation at the quark level

Abstract

In small collision systems strange hadrons are suppressed, and the suppression grows with the number of strange quarks. Exact strangeness conservation in a finite volume accounts for this, but when it is imposed on hadrons it leaves the $ϕ$ meson unsuppressed, contrary to observation. We impose the conservation law on the strange quarks in a causally connected cluster, before hadronization, and count separately the combinations of a strange quark with the antiquark created together with it. A pair created from the vacuum cannot form a $ϕ$, a pair created from a gluon can only if it loses its color. With one function of multiplicity, the mean number of strange quarks per cluster, the model describes kaons, $ϕ$, $Ξ$ and $Ω$ in pp and p--Pb collisions at the LHC; the data require that about half of the same-pair combinations are excluded from the $ϕ$, and reject both an unsuppressed $ϕ$ and a $ϕ$ built only from different pairs at about five standard deviations. The same-pair combinations are those that carry the spin correlation observed in $Λ\barΛ$ production, whose dilution is thereby tied to the $ϕ$ suppression and is predicted to decrease with multiplicity