Annihilation dynamics plays a fundamental role in the baryon$-$antibaryon interaction (B$-\rm{\overline{B}}$) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the p$-\rm{\overline{p}}$ system but not in the low relative momentum region. Data regarding the B$-\rm{\overline{B}}$ interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon$-$antinucleon (N$-\rm{\overline{N}}$) results, when available. In this letter we present a measurement of the p$-\rm{\overline{p}}$, p$-\overline{\Lambda}\oplus\rm{\overline{p}}-\Lambda$ and $\Lambda-\overline{\Lambda}$ interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at $\sqrt{s} = 13$ TeV recorded by ALICE at the LHC. In the p$-\rm{\overline{p}}$ system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent $\chi\rm{EFT}$ potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednick\'y$-$Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental p$-\overline{\Lambda}\oplus\rm{\overline{p}}-\Lambda$ and $\Lambda-\overline{\Lambda}$ correlations. The model describes the $\Lambda-\overline{\Lambda}$ data and underestimates the p$-\overline{\Lambda}\oplus\rm{\overline{p}}-\Lambda$ data in the region of momenta below 200 MeV/$c$. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons.
Phys. Lett. B 829 (2022) 137060
HEP Data
e-Print: arXiv:2105.05190 | PDF | inSPIRE
CERN-EP-2021-083
Figure 2
Measured correlation function of $p-\overline{p}$ pairs. Statistical (bars) and systematic (boxes) uncertainties are shown separately. The Coulomb only interaction is shown by the green band. The blue band represents the fit performed using $\rm N^3$LO \chiEFT potentials with elastic and $n-\overline{n}$ coupled-channel. The inclusion of annihilation channels is shown by the red band, along with the $C_{\rm{background}}(k^*)$, multiplied by the normalization constant $N_D$ obtained in the fit. The reported average $\chi^2/\rm NDF$ is evaluated in the $k^*$ interval $[0,400]$ \MeVc and it includes correlations between the data points. Lower panel: $n_\sigma$ deviation between data and model in terms of numbers of statistical standard deviations. |  |
Figure 3
Measured correlation function of $p-\overline{\Lambda}$ (left) and $\Lambda-\overline{\Lambda}$ (right) pairs for two representative $m_T$ bins. Statistical (bars) and systematic (boxes) uncertainties are shown separately. Results using the Lednicky-Lyuboshits formula with $Pb-Pb$ scattering parameters are shown in light green. Orange bands are the results with $d_0$ and $Imf_0$ as free parameters. In grey the corresponding $C_{\rm{background}}(k^*)$, multiplied by the normalization constant $N_D$, is shown. The reported average $\chi^2/\rm NDF$ is evaluated in the $k^*$ interval $[0,400]$ MeV/c and it includes correlations between the data points. Lower panel: same as in Fig.2. |   |
Figure A.3
Measured correlation function of \pap pairs. Statistical (bars) and systematic (boxes) uncertainties are shown separately. The results assuming the \Ledn model with Coulomb included, as in , are shown by the violet band. The scattering parameters used as input for the \Ledn calculations include only the \nan contribution as coupled-channel . The model completely underestimates the \ks region from 50 to 150 \MeVc. As can be seen in Fig. \ref{fig:pApCFs}, the annihilation channels play a role in this intermediate region and a better description of the data is achieved when using the Migdal-Watson approximation to include them. This is a clear indication that the multi-meson channels are explicitly needed to model the current measured \pap correlation function. The \Ledn calculation also overestimates the coupling to the \nan channel, as can be seen from the large cusp structure at $\ks\approx50$ \MeVc not present in the data. Lower panel: $n_\sigma$ deviation between data and model in terms of numbers of statistical standard deviations. |  |