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| CMS-HIN-21-006 ; CERN-EP-2022-280 | ||
| $ \mathrm{K^0_S} $ and $ \Lambda $ ($ \overline{\Lambda} $) two-particle femtoscopic correlations in PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 13 January 2023 | ||
| Phys. Lett. B 857 (2024) 138936 | ||
| Abstract: Two-particle correlations are presented for $ \mathrm{K^0_S} $, $ \Lambda $, and $ \overline{\Lambda} $ strange hadrons as a function of relative momentum in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The dataset corresponds to an integrated luminosity of 0.607 nb$^{-1}$ and was collected using the CMS detector at the CERN LHC. These correlations are sensitive to quantum statistics and to final-state interactions between the particles. The source size extracted from the $ \mathrm{K^0_S}\mathrm{K^0_S} $ correlations is found to decrease from 4 to 1 fm in going from central to peripheral collisions. Strong interaction scattering parameters (i.e., scattering length and effective range) are determined from the $ \Lambda\mathrm{K^0_S} $ and $ \Lambda\Lambda $ (including their charge conjugates) correlations using the Lednicky-Lyuboshitz model and are compared to theoretical and other experimental results. | ||
| Links: e-print arXiv:2301.05290 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The invariant mass of $ \mathrm{K^0_S} $ (left) and $ \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 (red) line for the total fit, and a dashed (green) line for the background fit. The vertical dashed-dotted (pink) lines indicate the peak region and the vertical dashed (blue) lines indicate the sideband regions. |
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Figure 1-a:
The invariant mass of $ \mathrm{K^0_S} $, and the corresponding fit in the 0-80% centrality range. The circles are the data, and the fit is shown with a solid (red) line for the total fit, and a dashed (green) line for the background fit. The vertical dashed-dotted (pink) lines indicate the peak region and the vertical dashed (blue) lines indicate the sideband regions. |
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Figure 1-b:
The invariant mass of $ \Lambda $, and the corresponding fit in the 0-80% centrality range. The circles are the data, and the fit is shown with a solid (red) line for the total fit, and a dashed (green) line for the background fit. The vertical dashed-dotted (pink) lines indicate the peak region and the vertical dashed (blue) lines indicate the sideband regions. |
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Figure 2:
The correlation distributions and fits for $ \mathrm{K^0_S}\mathrm{K^0_S} $ pairs in different centrality ranges, starting from 0-10% centrality to 50-60% centrality, with 0 $ < k_{\mathrm{T}} < $ 2.5 GeV. In each plot, the red circles are the data, the blue solid line is the fit using Eq. (8), and the green dotted line is the non-femtoscopic background from Eq. (7). The $ \chi^2 $ and dof values are for the full $ q_{\text{inv}} $ range. The insert plots show the data and the fit for the $ q_{\text{inv}} < $ 0.4 GeV region, with the $ \chi^2 $ and number of bins evaluated in that region. |
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Figure 3:
The correlation distributions and fits for $ \Lambda\mathrm{K^0_S} $ (left) and $ \Lambda\Lambda $ (right) pairs with 0-80% centrality and no restriction on $ k_{\mathrm{T}} $. In each plot, the red circles are the data, the blue solid line is the fit using Eq. (8), and the green dotted line is the non-femtoscopic background from Eq. (7). The $ \chi^2 $ and dof values are for the full $ q_{\text{inv}} $ range. The insert plots show the data and the fit for the $ q_{\text{inv}} < $ 0.4 GeV region, with the $ \chi^2 $ and number of bins evaluated in that region. |
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Figure 3-a:
The correlation distributions and fits for $ \Lambda\mathrm{K^0_S} $ $ \Lambda\Lambda $ pairs with 0-80% centrality and no restriction on $ k_{\mathrm{T}} $. The red circles are the data, the blue solid line is the fit using Eq. (8), and the green dotted line is the non-femtoscopic background from Eq. (7). The $ \chi^2 $ and dof values are for the full $ q_{\text{inv}} $ range. The insert plot shows the data and the fit for the $ q_{\text{inv}} < $ 0.4 GeV region, with the $ \chi^2 $ and number of bins evaluated in that region. |
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Figure 3-b:
The correlation distributions and fits for $ \Lambda\mathrm{K^0_S} $ (left) and $ \Lambda\Lambda $ (right) pairs with 0-80% centrality and no restriction on $ k_{\mathrm{T}} $. In each plot, the red circles are the data, the blue solid line is the fit using Eq. (8), and the green dotted line is the non-femtoscopic background from Eq. (7). The $ \chi^2 $ and dof values are for the full $ q_{\text{inv}} $ range. The insert plots show the data and the fit for the $ q_{\text{inv}} < $ 0.4 GeV region, with the $ \chi^2 $ and number of bins evaluated in that region. |
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Figure 4:
The $ R_{\text{inv}} $ (left) and $ \lambda $ parameter (right) as a function of centrality. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively. |
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Figure 4-a:
The $ R_{\text{inv}} $ parameter as a function of centrality. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively. |
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Figure 4-b:
The $ \lambda $ parameter as a function of centrality. For each data point, the line and shaded area indicate the statistical and systematic uncertainty, respectively. |
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Figure 5:
The measured values of $ d_0 $ versus $ \Re \, f_0 $ (left) and $ \Im \, f_0 $ versus $ \Re \, f_0 $ (right) from this analysis along with other measurements and predictions as described in the text. For each data point, the lines and the boxes indicate the (one-dimensional) statistical and systematic uncertainties, respectively. |
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Figure 5-a:
The measured values of $ d_0 $ versus $ \Re \, f_0 $ (left) and $ \Im \, f_0 $ versus $ \Re \, f_0 $ (right) from this analysis along with other measurements and predictions as described in the text. For each data point, the lines and the boxes indicate the (one-dimensional) statistical and systematic uncertainties, respectively. |
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Figure 5-b:
The measured values of $ d_0 $ versus $ \Re \, f_0 $ (left) and $ \Im \, f_0 $ versus $ \Re \, f_0 $ (right) from this analysis along with other measurements and predictions as described in the text. For each data point, the lines and the boxes indicate the (one-dimensional) statistical and systematic uncertainties, respectively. |
| Tables | |
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Table 1:
Summary of absolute systematic uncertainties in $ \mathrm{K^0_S}\mathrm{K^0_S} $, $ \Lambda\mathrm{K^0_S} $ and $ \Lambda\Lambda $ correlation measurements. The values for $ R_{\text{inv}} $, $ d_0 $, $ \Re \, f_0 $, and $ \Im \, f_0 $ are in fm. |
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Table 2:
Extracted values of the $ R_{\text{inv}} $, $ \Re \, f_0 $, $ \Im \, f_0 $, $ d_0 $, $ \lambda $, and $ \left < m_{\mathrm{T}}\right > $ parameters from the $ \mathrm{K^0_S}\mathrm{K^0_S} $, $ \Lambda\mathrm{K^0_S} $, and $ \Lambda\Lambda $ combinations in the 0-80% centrality range. The first and second uncertainties are statistical and systematic, respectively. |
| Summary |
| The $ \mathrm{K^0_S}\mathrm{K^0_S} $, $ \Lambda\mathrm{K^0_S} $, and $ \Lambda\Lambda $ femtoscopic correlations are studied using lead-lead (PbPb) collision data at a center-of-mass energy per nucleon pair of $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV, collected by the CMS Collaboration. This is the first report on $ \Lambda\Lambda $ correlations in PbPb collisions at the CERN LHC. The source size $ R_{\text{inv}} $ and the incoherence parameter $ \lambda $ were extracted for $ \mathrm{K^0_S}\mathrm{K^0_S} $ correlations in six centrality bins covering the 0-60% range. The value of $ R_{\text{inv}} $ decreases from 4 to 1 fm going from central to peripheral collisions and agrees with results from the ALICE Collaboration at a similar transverse mass. Along with the $ R_{\text{inv}} $ and $ \lambda $ parameters, the strong interaction scattering parameters, i.e.,, the complex scattering length and effective range, were extracted from $ \Lambda\mathrm{K^0_S} $ and $ \Lambda\Lambda $ correlations in the 0-80% centrality range. These scattering parameters indicate that the $ \Lambda\mathrm{K^0_S} $ interaction is repulsive and that the $ \Lambda\Lambda $ interaction is attractive. The scattering parameters obtained from $ \Lambda\mathrm{K^0_S} $ correlations differ from those reported by the ALICE Collaboration. The positive real scattering length obtained from the $ \Lambda\Lambda $ correlation disfavors the existence of a bound H-dibaryon state. The $ \Lambda\Lambda $ scattering parameters help to constrain baryon-baryon and, more specifically, hyperon-hyperon interaction models. These measurements provide an additional input to understand the nature of the strong interaction between pairs of strange hadrons. |
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