# Measuring K$^0_{\rm S}$K$^{\rm \pm}$ interactions using Pb-Pb collisions at ${\sqrt{s_{\rm NN}}=2.76}$ TeV

We present the first ever measurements of femtoscopic correlations between the K$^0_{\rm S}$ and K$^{\rm \pm}$ particles. The analysis was performed on the data from Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the $a_0(980)$ resonance. The extracted kaon source radius and correlation strength parameters for K$^0_{\rm S}$K$^{\rm -}$ are found to be equal within the experimental uncertainties to those for K$^0_{\rm S}$K$^{\rm +}$. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the $a_0$ resonance are constrained. Our results are also compatible with the interpretation of the $a_0$ having a tetraquark structure over that of a diquark.

Submitted to: PLB
e-Print: arXiv:1705.04929 | PDF | inSPIRE
CERN-EP-2017-063

Figures

## Figure 1

 Examples of raw K$^0_{\rm S}$K$^{\rm +}$ correlation functions for the three $k_T$ bins with linear fits to the baseline at large $k^*$. Statistical uncertainties are shown.

## Figure 2

 Examples of K$^0_{\rm S}$K$^+$ and K$^0_{\rm S}$K$^-$ correlation functionsdivided by linear fits to the baselinewith the Lednicky parameterization using the Achasov2 parameters. Statistical (lines) and the linear sum of statistical and systematic uncertainties (boxes) are shown.

## Figure 3

 Sample results for the $R$ and $\lambda$ parameters extracted in thepresent analysis from K$^0_{\rm S}$K$^{\rm \pm}$ femtoscopy using the Achasov1parameters. The left column compares K$^0_{\rm S}$K$^{\rm +}$and K$^0_{\rm S}$K$^{\rm -}$ results from the quadratic baseline fit method, and the right columncompares results averaged over K$^0_{\rm S}$K$^{\rm +}$and K$^0_{\rm S}$K$^{\rm -}$ for the quadratic baseline fits and the linear baseline fits Statistical uncertainties are plotted for all results.

## Figure 4

 Source radius parameter, $R$, extracted in the present analysis fromK$^0_{\rm S}$K$^{\rm \pm}$ femtoscopy averaged over K$^0_{\rm S}$K$^{\rm +}$and K$^0_{\rm S}$K$^{\rm -}$ and the two baseline fit methods (red symbols),along withcomparisons with identical kaon results from ALICE~ (blue symbols) Statistical (lines) and the linear sum of statistical and systematic uncertainties (boxes) are shown.

## Figure 5

 Correlation strength parameter, $\lambda$, extracted in the present analysis fromK$^0_{\rm S}$K$^{\rm \pm}$ femtoscopy averaged over K$^0_{\rm S}$K$^{\rm +}$and K$^0_{\rm S}$K$^{\rm -}$ and the two baseline fit methods (red symbols), along withcomparisons with identical kaon results from ALICE~ (blue symbols) Statistical (lines) and the linear sum of statistical and systematic uncertainties (boxes) are shown.