Kaon–proton strong interaction at low relative momentum via femtoscopy in Pb–Pb collisions at the LHC

The ALICE collaboration
Phys.Lett.B 822 (2021) 136708, 2021.

Abstract (data abstract)
CERN-LHC. In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb--Pb collisions at the LHC provide an accurate measurement of kaon--proton scattering parameters at low relative momentum, allowing precise access to the K- p --> K- p process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of K- p (K+ ap) and $\K+ p (k- ap) pairs in Pb--Pb collisions at centre-of-mass energy per nucleon pair of Sqrt(s_NN)=5.02~TeV registered by the ALICE experiment is reported. The components of the K- p complex scattering length are extracted and found to be Re f_0=-0.91 +/- ~{0.03}(stat)^{+0.17}_{-0.03}(syst) and Im f_0 = 0.92+/-~{0.05}(stat)^{+0.12}_{-0.33}(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.

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