K$^0_s$K$^0_s$ correlations in pp collisions at $\sqrt{s}=7$ TeV from the LHC ALICE experiment

Identical neutral kaon pair correlations are measured in $\sqrt{s}=7$ TeV pp collisions in the ALICE experiment. One-dimensional K$^0_s$K$^0_s$ correlation functions in terms of the invariant momentum difference of kaon pairs are formed in two multiplicity and two transverse momentum ranges. The femtoscopic parameters for the radius and correlation strength of the kaon source are extracted. The f${\rm i}$t includes quantum statistics and final-state interactions of the a$_0$/f$_0$ resonance. K$^0_s$K$^0_s$ correlations show an increase in radius for increasing multiplicity and a slight decrease in radius for increasing transverse mass, $m_{\rm T}$, as seen in $\pi\pi$ correlations in the pp system and in heavy-ion collisions. Transverse mass scaling is observed between the K$^0_s$K$^0_s$ and $\pi\pi$ radii. Also, the f${\rm i}$rst observation is made of the decay of the f$_2'$(1525) meson into the K$^0_s$K$^0_s$ channel in pp collisions.

Figures

Figure 1

Invariant mass distributionsof $\pi^+\pi^-$ pairs in the four multiplicit-$k_{\rm T}$ ranges used in the study. K$^0_s$ used in this analysis were identif${\rm i}$ed by the cut 0.490 GeV/$c^2$ $< m < $ 0.504 GeV/$c^2$. Also shown is a Gaussian+linear f${\rm i}$t to the data points.
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Figure 2

Inclusive (all event multiplicities and $k_{\rm T}$) K$^0_s$K$^0_s$ $Q_{\rm inv}$correlation function. Plotted in the insert to the figure is the invariant K$^0_s$K$^0_s$ mass distribution, d$N$/d$m$(K$^0_s$K$^0_s$), in the vicinity of the small peak at $Q_{\rm inv}\approx1.15$ GeV/$c$.
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Figure 3

Ratio of K$^0_s$K$^0_s$ experimental background to PYTHIA background vs. $Q_{\rm inv}$ for the range $N_{\rm ch}$ 1-11, $k_{\rm T}< 0.85$ GeV/c. The average of the ratio is normalized to unity.
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Figure 4

Experimental and PYTHIA K$^0_s$K$^0_s$ correlation functions for the four multiplicity-$k_{\rm T}$ ranges.
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Figure 5

Experimental K$^0_s$K$^0_s$ correlation functions divided by PYTHIA correlation functions for the four multiplicity-$k_{\rm T}$ ranges with femtoscopic f${\rm i}$ts using the Lednicky parametrization.
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Figure 6

$\lambda$ parameters extracted by fitting the Lednicky parametrization to K$^0_s$K$^0_s$ correlation functions as shown in Figure 5. Statistical (darker lines) and total errors are shown. The $N_{\rm ch}>11$ points are offset by 0.05 GeV/$c^2$ for clarity.
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Figure 7

$R$ parameters extracted by fitting the Lednicky parametrization to K$^0_s$K$^0_s$ correlation functions as shown in Figure 5. Also shown for comparison are $R$ parameters extracted in the same event multiplicity ranges from a $\pi\pi$ femtoscopic study by ALICE in pp collisions at $\sqrt{s}=7$ TeV. Statistical (darker lines) and total errors are shown. The highest $m_{\rm T}$ pion $N_{\rm ch}>11$ point and lower $m_{\rm T}$ kaon $N_{\rm ch}>11$ point have been shifted by 0.03 GeV/$c^2$ for clarity.
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