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The production of the $\psi \left(2S\right)$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 $\psi \left(2S\right)$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 $[{\sigma }^{\psi \left(2S\right)}/{\sigma }^{J/\psi }{]}_{\mathrm{Pb}\text{−}\mathrm{Pb}}/[{\sigma }^{\psi \left(2S\right)}/{\sigma }^{J/\psi }{]}_{pp}$. It is found that in Pb-Pb collisions the $\psi \left(2S\right)$is suppressed by a factor of $\sim 2$with respect to the $J/\psi$. The $\psi \left(2S\right)$nuclear modification factor $R_{\mathrm{AA}}$was also obtained as a function of both centrality and $p_T$. The results show that the $\psi \left(2S\right)$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. 

A bstract The first measurement of the e + e − pair production at low lepton pair transverse momentum ( p T , ee ) and low invariant mass ( m ee ) in non-central Pb–Pb collisions at $$ {\sqrt{s}}_{\textrm{NN}} $$ s NN = 5 . 02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity ( |η e | < 0 . 8) as a function of invariant mass (0.4 ≤ m ee < 2 . 7 GeV/ c 2 ) in the 50–70% and 70–90% centrality classes for p T , ee < 0.1 GeV/ c , and as a function of p T , ee in three m ee intervals in the most peripheral Pb–Pb collisions. Below a p T , ee of 0.1 GeV/ c , a clear excess of e + e − pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The m ee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the p T , ee spectra. The measured $$ \sqrt{\left\langle {p}_{\textrm{T},\textrm{ee}}^2\right\rangle } $$ p T , ee 2 of the excess p T , ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region. 

A bstract The first measurements of elliptic flow of π ± , K ± , $$ \textrm{p}+\overline{\textrm{p}} $$ p + p ¯ , $$ {\textrm{K}}_{\textrm{S}}^0 $$ K S 0 , $$ \Lambda +\overline{\Lambda} $$ Λ + Λ ¯ , ϕ , $$ {\Xi}^{-}+{\overline{\Xi}}^{+} $$ Ξ − + Ξ ¯ + , and $$ {\varOmega}^{-}+{\overline{\varOmega}}^{+} $$ Ω − + Ω ¯ + using multiparticle cumulants in Pb–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV are resented. Results obtained with two- ( v 2 {2}) and four-particle cumulants ( v 2 {4}) are shown as a function of transverse momentum, p T , for various collision centrality intervals. Combining the data for both v 2 {2} and v 2 {4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous p T -differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low p T and the approximate scaling with the number of constituent quarks at intermediate p T , are similarly present in the four-particle correlations and the combinations of v 2 {2} and v 2 {4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide p T range.