Investigating the composition of the K₀^⁎(700) state with π^±K_S⁰ correlations at the LHC

The first measurements of femtoscopic correlations with the particle pair combinations π^±K_S⁰ in pp collisions at s=13 TeV at the Large Hadron Collider (LHC) are reported by the ALICE experiment. Using the femtoscopic approach, it is shown that it is possible to study the elusive K₀^⁎(700) particle that has been considered a tetraquark candidate for over forty years. Source and final-state interaction parameters are extracted by fitting a model assuming a Gaussian source to the experimentally measured two-particle correlation functions. The final-state interaction in the π^±K_S⁰ system is modeled through a resonant scattering amplitude, defined in terms of a mass and a coupling parameter, The extracted mass and Breit–Wigner width, derived from the coupling parameter, of the final-state interaction are found to be consistent with previous measurements of the K₀^⁎(700). The small value and increase of the correlation strength with increasing source size support the hypothesis that the K₀^⁎(700) is a four-quark state, i.e. a tetraquark state of the form (q₁,q₂‾,q₃,q₃‾) in which q₁, q₂ and q₃ indicate the flavor of the valence quarks of the π and K_S⁰. This latter trend is also confirmed via a simple geometric model that assumes a tetraquark structure of the K₀^⁎(700) resonance.