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Measurement of strange baryon–antibaryon interactions with femtoscopic correlations

The ALICE collaboration
Phys.Lett.B 802 (2020) 135223, 2020.

Abstract (data abstract)
Measurement of $\rm p\overline{\Lambda}\oplus\overline{p}\Lambda$ and $\Lambda\overline{\Lambda}$ interactions with femtoscopic correlations in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$~{\normalfont TeV} and $\sqrt{s_{\rm NN}} = 5.02$~{\normalfont TeV} LHC ALICE collaboration Baryon-antibaryon correlations in Pb-Pb collisions minimum bias trigger, -0.8 < eta < 0.8 Femtoscopic correlation functions were measured for $\rm p\overline{p}$, $\rm p\overline{\Lambda}\oplus\overline{p}\Lambda$, and $\Lambda\overline{\Lambda}$ pairs, as a function of collision centrality, in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$~TeV and $\sqrt{s_{\rm NN}}=5.02$~TeV recorded by the ALICE experiment at the LHC. %They reflect the geometry of the emitting source convoluted with the characteristic final state interactions for each pair, with the strong force playing a dominant role. Correlations present in heavier baryon pairs directly influence the measurement via the so-called residual correlations mechanism. A simultaneous fit to all obtained correlation functions was performed, maximising the precision and sensitivity to the strong interaction parameters for the selected baryon pairs. Real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined $\rm p\overline{\Lambda}\oplus\overline{p}\Lambda$ pairs and, for the first time, for $\Lambda\overline{\Lambda}$ pairs. Effective averaged scattering parameters for heavier baryon--anti-baryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon--anti-baryon pairs, suggesting that they annihilate in the same manner as $\rm p\overline{p}$ at the same pair relative momentum $k^{*}$. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length open up a possibility for future baryon--anti-baryon bound state searches.

  • Figure 1 top left

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    10.17182/hepdata.96956.v1/t1

    p pbar correlation function for centrality 10-20% from Pb-Pb collisions at 5.02 TeV

  • Figure 1 top right

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    10.17182/hepdata.96956.v1/t2

    p pbar correlation function for centrality 10-20% from Pb-Pb collisions at 2.76 TeV

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    p LambdaBar plus pbar Lambda correlation function for centrality 10-20% from Pb-Pb collisions at 5.02 TeV

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    p LambdaBar plus pbar Lambda correlation function for centrality 10-20% from Pb-Pb collisions at 2.76 TeV

  • Figure 1 bottom left

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    Lambda LambdaBar plus pbar Lambda correlation function for centrality 10-20% from Pb-Pb collisions at 5.02 TeV

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    10.17182/hepdata.96956.v1/t6

    Lambda LambdaBar plus pbar Lambda correlation function for centrality 10-20% from Pb-Pb collisions at 2.76 TeV

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