# Scattering studies with low-energy kaon-proton femtoscopy in proton-proton collisions at the LHC

The study of the strength and behaviour of the antikaon-nucleon ($\mathrm{\overline{K}N}$) interaction constitutes one of the key focuses of the strangeness sector in low-energy Quantum Chromodynamics (QCD). In this letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K$^+$ p $\oplus$ K$^-$ $\overline{\mathrm{p}}$) and (K$^-$ p $\oplus$ K$^+$ $\overline{\mathrm{p}}$) pairs measured in pp collisions at $\sqrt{s}$ = 5, 7 and 13 TeV are reported. A structure observed around a relative momentum of 58 MeV/$c$ in the measured correlation function of (K$^-$ p $\oplus$ K$^+$ $\overline{\mathrm{p}}$) constitutes the first experimental evidence for the opening of the $(\mathrm{\overline{K}^0 n} \oplus \mathrm{K^0 \overline{n}})$ isospin breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to several models. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the $\mathrm{\overline{K}N}$ threshold for low-energy QCD chiral models.

Submitted to: PRL
e-Print: arXiv:1905.13470 | PDF | inSPIRE

Figures

## Figure 1

 (\kp p \opl\ \km \ap) correlation functions obtained from pp collisions at \s~=~5~TeV (left), 7 TeV (middle) and 13 TeV (right) fitted with Eq.~\ref{eq:cf1} including only a Coulomb interaction (blue) or in addition the strong interaction implemented in the J\"ulich model (red). The measurement is shown by the black markers, the vertical lines and the boxes represent the statistical and systematic uncertainties respectively. In the bottom panels of the figure, the difference between the data and models are shown. The bands represent the systematic uncertainty related to the determination of the $\lambda$ parameter and to the source radius.

## Figure 2

 (\km p \opl\ \kp \ap) correlation functions obtained from pp collisions at \s~=~5~TeV (left), 7 TeV (middle) and 13 TeV (right) fitted with Eq.~\ref{eq:cf1}. The measurement is presented by the black markers, the vertical lines and the boxes represent the statistical and systematic uncertainties respectively. Three different potentials were considered: Coulomb potential (blue band), Kyoto model~ (light blue band), J\"ulich model~ where the physics masses of \km\ and \kzero are used~ with the Coulomb interaction included (red band). In the bottom panels, differences between data and model are shown. The bands represent the systematic uncertainty related to the determination of the $\lambda$ parameter and to the source radius.