CMS-PAS-HIN-21-006

CMS-PAS-HIN-21-006
Two-particle femtoscopic correlation measurements of $\mathrm{K^{0}_{S}}$ and $\Lambda (\overline{\Lambda})$ particles in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV
CMS Collaboration
June 2022

Abstract: Two-particle correlations as a function of relative momentum are presented for $\mathrm{K^{0}_{S}}$ , $\Lambda$ , and $\overline{\Lambda}$ strange hadrons produced in lead-lead collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The data were obtained using the CMS detector at the LHC. Such correlations are sensitive to quantum statistics and to possible final-state interactions between the particles. Source radii extracted from $\mathrm{K^{0}_{S}K^{0}_{S}}$ correlations in different centrality regions are found to decrease in going from central to peripheral collisions. Strong-interaction scattering parameters (i.e., scattering length and effective range) are determined from $\Lambda\mathrm{K^{0}_{S}}\oplus\overline{\Lambda}\mathrm{K^{0}_{S}}$ and $\Lambda\Lambda\oplus\overline{\Lambda}\overline{\Lambda}$ correlations using the Lednicky-Lyuboshits model and compared to other experimental and theoretical results.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The invariant mass of ${\mathrm {K^0_S}}$ (left) and $\Lambda{+}\overline {\Lambda}$ (right), and their corresponding fits in the 0-80% centrality range. The circles are the data, and the fit is shown with a solid curve for the total fit, a dashed-dotted curve for the signal component, and a dashed curve for the background component. The vertical lines indicate the $\pm$ 2 $\sigma$ peak region.
png pdf	Figure 1-a: The invariant mass of ${\mathrm {K^0_S}}$ (left) and $\Lambda{+}\overline {\Lambda}$ (right), and their corresponding fits in the 0-80% centrality range. The circles are the data, and the fit is shown with a solid curve for the total fit, a dashed-dotted curve for the signal component, and a dashed curve for the background component. The vertical lines indicate the $\pm$ 2 $\sigma$ peak region.
png pdf	Figure 1-b: The invariant mass of ${\mathrm {K^0_S}}$ (left) and $\Lambda{+}\overline {\Lambda}$ (right), and their corresponding fits in the 0-80% centrality range. The circles are the data, and the fit is shown with a solid curve for the total fit, a dashed-dotted curve for the signal component, and a dashed curve for the background component. The vertical lines indicate the $\pm$ 2 $\sigma$ peak region.
png pdf	Figure 2: The correlation distributions and fits for the ${\mathrm {K^{0}_{S}K^{0}_{S}}}$ pair for the 20-30% centrality range (left), and the ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ (right) and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ (bottom) pairs with 0-80% centrality. In these plots, red circles are the experimental results, the blue solid line is the fit using Eq. (7), and the green dotted line is the nonfemtoscopic background from Eq. (6).
png pdf	Figure 2-a: The correlation distributions and fits for the ${\mathrm {K^{0}_{S}K^{0}_{S}}}$ pair for the 20-30% centrality range (left), and the ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ (right) and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ (bottom) pairs with 0-80% centrality. In these plots, red circles are the experimental results, the blue solid line is the fit using Eq. (7), and the green dotted line is the nonfemtoscopic background from Eq. (6).
png pdf	Figure 2-b: The correlation distributions and fits for the ${\mathrm {K^{0}_{S}K^{0}_{S}}}$ pair for the 20-30% centrality range (left), and the ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ (right) and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ (bottom) pairs with 0-80% centrality. In these plots, red circles are the experimental results, the blue solid line is the fit using Eq. (7), and the green dotted line is the nonfemtoscopic background from Eq. (6).
png pdf	Figure 2-c: The correlation distributions and fits for the ${\mathrm {K^{0}_{S}K^{0}_{S}}}$ pair for the 20-30% centrality range (left), and the ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ (right) and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ (bottom) pairs with 0-80% centrality. In these plots, red circles are the experimental results, the blue solid line is the fit using Eq. (7), and the green dotted line is the nonfemtoscopic background from Eq. (6).
png pdf	Figure 3: Left: $R_{\text {inv}}$ as a function of centrality by considering only the QS (blue circle), and both the QS and FSI effects (red circles). Right: $R_{\text {inv}}$ as a function of $m_{\mathrm {T}}$ (dark markers) and compared with ALICE data (light markers) for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV [27] in 0-10, 10-30, and 30-50% centrality classes. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively.
png pdf	Figure 3-a: Left: $R_{\text {inv}}$ as a function of centrality by considering only the QS (blue circle), and both the QS and FSI effects (red circles). Right: $R_{\text {inv}}$ as a function of $m_{\mathrm {T}}$ (dark markers) and compared with ALICE data (light markers) for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV [27] in 0-10, 10-30, and 30-50% centrality classes. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively.
png pdf	Figure 3-b: Left: $R_{\text {inv}}$ as a function of centrality by considering only the QS (blue circle), and both the QS and FSI effects (red circles). Right: $R_{\text {inv}}$ as a function of $m_{\mathrm {T}}$ (dark markers) and compared with ALICE data (light markers) for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV [27] in 0-10, 10-30, and 30-50% centrality classes. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively.
png pdf	Figure 4: The $\lambda$ parameter as a function of centrality by considering only the QS (blue circles) and both the QS and FSI effects (red circles). For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively.
png pdf	Figure 5: The values of $d_{0}$ and $\Re f_{0}$ (left) and the values of $\Im f_{0}$ and $\Re f_{0}$ (right). In the left plot, the blue triangles and square markers are for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations, respectively, and are compared with the ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ result from the STAR experiment [28] and ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ results from ALICE experiment [27]. A reanalysis of STAR data for ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations is shown in the shaded area [32]. Theory calculations of the ${\Lambda \Lambda}$ interaction parameters are shown as black triangles [33,34]. The blue dotted lines correspond to the relation $d_{0} = {\|\Re {f_{0}}\|}/{2}$ . In the right plot, the triangle is for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ correlations, and is compared with the ALICE ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ result [27]. For each data point, the two lines and the box indicate the (one-dimensional) statistical and systematic uncertainties, respectively.
png pdf	Figure 5-a: The values of $d_{0}$ and $\Re f_{0}$ (left) and the values of $\Im f_{0}$ and $\Re f_{0}$ (right). In the left plot, the blue triangles and square markers are for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations, respectively, and are compared with the ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ result from the STAR experiment [28] and ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ results from ALICE experiment [27]. A reanalysis of STAR data for ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations is shown in the shaded area [32]. Theory calculations of the ${\Lambda \Lambda}$ interaction parameters are shown as black triangles [33,34]. The blue dotted lines correspond to the relation $d_{0} = {\|\Re {f_{0}}\|}/{2}$ . In the right plot, the triangle is for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ correlations, and is compared with the ALICE ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ result [27]. For each data point, the two lines and the box indicate the (one-dimensional) statistical and systematic uncertainties, respectively.
png pdf	Figure 5-b: The values of $d_{0}$ and $\Re f_{0}$ (left) and the values of $\Im f_{0}$ and $\Re f_{0}$ (right). In the left plot, the blue triangles and square markers are for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations, respectively, and are compared with the ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ result from the STAR experiment [28] and ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ results from ALICE experiment [27]. A reanalysis of STAR data for ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations is shown in the shaded area [32]. Theory calculations of the ${\Lambda \Lambda}$ interaction parameters are shown as black triangles [33,34]. The blue dotted lines correspond to the relation $d_{0} = {\|\Re {f_{0}}\|}/{2}$ . In the right plot, the triangle is for ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ correlations, and is compared with the ALICE ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ result [27]. For each data point, the two lines and the box indicate the (one-dimensional) statistical and systematic uncertainties, respectively.

Tables
png pdf	Table 1: Summary of systematic uncertainties in ${\mathrm {K^{0}_{S}K^{0}_{S}}}$ correlations in different centrality bins
png pdf	Table 2: Summary of systematic uncertainties in ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ correlations in 0-80% centrality
png pdf	Table 3: Summary of systematic uncertainties in ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations in 0-80% centrality
png pdf	Table 4: Extracted values of the $R_{inv}$ , $\Re f_{0}$ , $\Im f_{0}$ , $d_{0}$ , and $\lambda$ from ${\Lambda \mathrm {K^0_S}\oplus \overline {\Lambda}\mathrm {K^0_S}}$ and ${\Lambda \Lambda \oplus \overline {\Lambda}\overline {\Lambda}}$ correlations in the 0-80% centrality.

Summary

The

${\mathrm{K^{0}_{S}K^{0}_{S}}}$ ,

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ , and

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ femtoscopic correlations are extracted from data collected in PbPb collisions at a center-of-mass energy per nucleon pair of

${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. This is the first report of

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ correlations in PbPb collisions. The source size

$R_{\text{inv}}$ is extracted for

${\mathrm{K^{0}_{S}K^{0}_{S}}}$ correlations in six equal width centrality bins covering the 0-60% centrality range and is found to decrease going towards more peripheral collisions. The extraction of

$R_{\text{inv}}$ as a function of

$m_{\mathrm{T}}$ is also presented for

${\mathrm{K^{0}_{S}K^{0}_{S}}}$ correlations and is compared with ALICE results at

${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV. Measured values for

$R_{\text{inv}}$ , based on

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ , and

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ correlations, are also presented for the 0-80% centrality range. The Lednicky-Lyuboshits model fits to the correlation data indicate that the

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ interaction is repulsive and

${\Lambda\mathrm{K^0_S}\oplus\overline{\Lambda}\mathrm{K^0_S}}$ interaction is attractive with no evidence for a bound H-dibaryon.

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