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Recent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried by${\mathrm{\Lambda }}_c^{+}$baryons,$z_{\parallel }^{\mathrm{ch}}$, in hadronic collisions. The results are obtained in proton-proton ($pp$) collisions at$\sqrt{s}=13\mathrm{TeV}$at the LHC, with${\mathrm{\Lambda }}_c^{+}$baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of$3\le p_T^{{\mathrm{\Lambda }}_c^{+}}<15\mathrm{GeV}/c$and$7\le p_T^{\text{jet ch}}<15\mathrm{GeV}/c$, respectively. The$z_{\parallel }^{\mathrm{ch}}$distribution is compared to a measurement of${\mathrm{D}}^0$-tagged charged jets in$pp$collisions as well as to 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronization models which include color correlations beyond leading-color in the string formation.

© 2024 CERN, for the ALICE Collaboration2024CERN 

The production of the$\psi (2S)$charmonium state was measured with ALICE in Pb-Pb collisions at$\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity ($2.5<y<4$). The measurement of the ratio of the inclusive production cross sections of the$\psi (2S)$and$\mathrm{J}/\psi$resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region$p_T<12\mathrm{GeV}/c$. The results are compared with the corresponding measurements in$pp$collisions, by forming the double ratio$[{\sigma }^{\psi (2S)}/{\sigma }^{J/\psi }{]}_{\mathrm{Pb}\text{−}\mathrm{Pb}}/[{\sigma }^{\psi (2S)}/{\sigma }^{J/\psi }{]}_{pp}$. It is found that in Pb-Pb collisions the$\psi (2S)$is suppressed by a factor of$\sim 2$with respect to the$J/\psi$. The$\psi (2S)$nuclear modification factor$R_{\mathrm{AA}}$was also obtained as a function of both centrality and$p_T$. The results show that the$\psi (2S)$resonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up to$\sim 3$with respect to$pp$. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and of$R_{\mathrm{AA}}$with higher-$p_T$results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the presence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.

© 2024 CERN, for the ALICE Collaboration2024CERN 

Abstract Three-body nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the three-nucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the three-body forces. In this work, we present the first direct measurement of the p–p–p and p–p– $$\Lambda $$ Λ systems in terms of three-particle correlation functions carried out for pp collisions at $$\sqrt{s} = 13$$ s = 13 TeV. Three-particle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the three-particle interaction contribution to these correlations can be isolated after subtracting the known two-body interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual three-body effect while for p–p– $$\Lambda $$ Λ the cumulant is consistent with zero. This measurement demonstrates the accessibility of three-baryon correlations at the LHC.