Investigation of K$^{+}$K$^{-}$ interactions via femtoscopy in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}} =2.76$ TeV at the LHC

Femtoscopic correlations of non-identical charged kaons ($\rm K^+ K^-$) are studied in Pb$-$Pb collisions at a center-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{NN}}} =2.76$ TeV by ALICE at the LHC. One-dimensional $\rm K^+ K^-$ correlation functions are analyzed in three centrality classes and eight intervals of particle-pair transverse momentum. The Lednick\'y and Luboshitz interaction model used in the $\rm K^+ K^-$ analysis includes the final-state Coulomb interactions between kaons and the final-state interaction through $a_{0}$(980) and $f_{0}$(980) resonances. The mass of $f_{0}$(980) and coupling were extracted from the fit to $\rm K^+ K^-$ correlation functions using the femtoscopic technique for the first time. The measured mass and width of the $f_{0}$(980) resonance are consistent with other published measurements. The height of the $\phi$(1020) meson peak present in the $\rm K^+ K^-$ correlation function rapidly decreases with increasing source radius, qualitatively in agreement with an inverse volume dependence. A phenomenological fit to this trend suggests that the $\phi$(1020) meson yield is dominated by particles produced directly from the hadronization of the system. The small fraction subsequently produced by FSI could not be precisely quantified with data presented in this paper and will be assessed in future work.

 

Accepted by: PRC
e-Print: arXiv:2211.15194 | PDF | inSPIRE
CERN-EP-2022-257
Figure group

Figure 1

Left: Single-kaon purity as a function of particle momentum $p$ for 0--10\%, 10--30\%, and 30--50\% centrality intervals Points are shifted along the $x$ axis for clarity Right: K$^+$K$^-$ pair purity as a function of pair transverse momentum $k_{\rm T}$. Systematic uncertainties are shown by bars Statistical uncertainties are smaller than the size of the markers.

Figure 2

The K$^+$K$^-$ experimental correlation functions corrected for non-flat baselines according to Eq. (\ref{eq:baseline})as a function of pair relative momentum $q$. The CFs are presented in threecentrality classes (rows): 0--10\%, 10\mbox{--}30\%, and 30--50\% and three pair transverse momentum $k_{\rm T}$ bins (columns): (0.3--0.4), (0.5--0.6) and (0.8\mbox{--}1.0) GeV/$c$ Statistical (bars) and systematic (boxes) uncertainties are shown. The red line shows thefit of the CF with the Lednick\'y--Lyuboshitz parametrization (Eq. (\ref{eq:Cfsi})) using free parameters (mass and couplings) for $f_0$(980) and Achasov  parameters for $a_0$(980) in the $0< q gev="" range="" the="" dashed-dotted="" lines="" correspond="" to="" baseline="" from="" eq.=""> < /q>

Figure 3

$R$ (left panel) and $\lambda$ (right panel) parameters as a function of pair transverse momentum $k_{\rm T}$ extracted in K$^+$K$^-$ analysis with free parameters (mass and couplings) for $f_0$(980) and Achasov  parameters for $a_0$(980) The parameters are compared to those obtained for identical charged kaons  Statistical (bars) and systematic (boxes) uncertainties are shown.

Figure 4

Height of $\phi$(1020) meson peak ($C_\phi$) as a function of source radius $R$, for three centrality classes Statistical uncertainties are shown by bars. Systematic uncertainties are smaller than the size of the markers. Blue solid line corresponds to the fit of CF with$C_\phi^{\rm direct} = {\rm const}/R^3$. Red dashed line corresponds to the fit with the second line in Eq. (\ref{eq:Cfsi}).