Abstract The azimuthal anisotropy of particles associated with jets (jet particles) at midrapidity is measured for the first time in p-Pb and Pb-Pb collisions at $$ \sqrt{{\textrm{s}}_{\textrm{NN}}} $$ s NN = 5.02 TeV down to transverse momentum (pT) of 0.5 GeV/c and 2 GeV/c, respectively, with ALICE. The results obtained in p-Pb collisions are based on a novel three-particle correlation technique. The azimuthal anisotropy coefficient v2 in high-multiplicity p-Pb collisions is positive, with a significance reaching 6.8σ at low pT, and its magnitude is smaller than in semicentral Pb-Pb collisions. In contrast to the measurements in Pb-Pb collisions, the v2 coefficient is also found independent of pT within uncertainties. Comparisons with the inclusive charged-particle v2 and with AMPT calculations are discussed. The predictions suggest that parton interactions play an important role in generating a non-zero jet-particle v2 in p-Pb collisions, even though they overestimate the reported measurement. These observations shed new insights on the understanding of the origin of the collective behaviour of jet particles in small systems such as p-Pb collisions, and provide significant stringent new constraints to models.

A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.

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 Λc+ baryons, z∥ch, in hadronic collisions. The results are obtained in proton-proton (pp) collisions at s=13 TeV at the LHC, with Λc+ baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of 3≤pTΛc+<15 GeV/c and 7≤pTjet ch<15 GeV/c, respectively. The z∥ch distribution is compared to a measurement of D0-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 Collaboration 2024 CERN

Collective behavior has been observed in high-energy heavy-ion collisions for several decades. Collectivity is driven by the high particle multiplicities that are produced in these collisions. At the CERN Large Hadron Collider (LHC), features of collectivity have also been seen in high-multiplicity proton-proton collisions that can attain particle multiplicities comparable to peripheral Pb-Pb collisions. One of the possible signatures of collective behavior is the decrease of femtoscopic radii extracted from pion and kaon pairs emitted from highmultiplicity collisions with increasing pair transverse momentum. This decrease can be described in terms of an approximate transverse mass scaling. In the present work, femtoscopic analyses are carried out by the ALICE Collaboration on charged pion and kaon pairs produced in pp collisions at root s = 13 TeV from the LHC to study possible collectivity in pp collisions. The event-shape analysis method based on transverse sphericity is used to select for spherical versus jetlike events, and the effects of this selection on the femtoscopic radii for both charged pion and kaon pairs are studied. This is the first time this selection method has been applied to charged kaon pairs. An approximate transverse-mass scaling of the radii is found in all multiplicity ranges studied when the difference in the Lorentz boost for pions and kaons is taken into account. This observation does not support the hypothesis of collective expansion of hot and dense matter that should only occur in high-multiplicity events. A possible alternate explanation of the present results is based on a scenario of common emission conditions for pions and kaons in pp collisions for the multiplicity ranges studied.

Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at √(s) = 13 TeV and p–Pb collisions at √(s_NN) = 5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle ∆φ and pseudorapidity separation ∆η for pairs of primary charged particles within the pseudorapidity interval |η| < 0.9 and the transverse-momentum interval 1 < pT < 4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6 < |∆η| < 1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.

The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high p_{T}) hadron trigger in proton-proton and central Pb-Pb collisions at sqrt[s_{NN}]=5.02  TeV. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter R=0.2, 0.4, and 0.5 in the range 7<p_{T,jet}<140  GeV/c and trigger-recoil jet azimuthal separation π/2<Δφ<π. The measurements exhibit a marked medium-induced jet yield enhancement at low p_{T} and at large azimuthal deviation from Δφ∼π. The enhancement is characterized by its dependence on Δφ, which has a slope that differs from zero by 4.7σ. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation.

The dependence of f(0)(980) production on the final-state charged-particle multiplicity in p-Pb collisions at root s(NN) = 5.02 TeV is reported. The production of f(0)(980) is measured with the ALICE detector via the f(0)(980) -> pi(+)pi(-) decay channel in a midrapidity region of -0.5 < y < 0. Particle yield ratios of f(0)(980) to pi and K*(892)(0) are found to be decreasing with increasing charged-particle multiplicity. The magnitude of the suppression of the f(0)(980)/pi and f(0)( 980)/K*(892)(0) yield ratios is found to be dependent on the transverse momentum p(T), suggesting different mechanisms responsible for the measured effects. Furthermore, the nuclear modification factor Q(pPb) of f(0)(980) is measured in various multiplicity ranges. The Q(pPb) shows a strong suppression of the f(0)(980) production in the p(T) region up to about 4 GeV/c. The results on the particle yield ratios and Q(pPb) for f(0)(980) may help to understand the late hadronic phase in p-Pb collisions and the nature of the internal structure of f(0)(980) particle.

Charged-particle jet yields have been measured in semicentral Pb–Pb collisions at center-of-mass energy per nucleon–nucleon collision sNN=5.02 TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-kT algorithm with resolution parameters R = 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb–Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum (< 50 GeV/c) R = 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2σ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss.

The production yields of the Σ(1385)± and Ξ(1530)0 resonances are measured in pp collisions at √(s) = 13 TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity ⟨dNch/dη⟩, which is related to the energy density produced in the collision. The results include transverse momentum (pT) distributions, pT-integrated yields, mean transverse momenta of Σ(1385)± and Ξ(1530)0, as well as ratios of the pT-integrated resonance yields relative to yields of other hadron species. The Σ(1385)±/π± and Ξ(1530)0/π± yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the Σ(1385)± and Ξ(1530)0 production in pp collisions at √(s) = 13 TeV.

The angular correlations between charged $\Xi$ baryons and associated identified hadrons (pions, kaons, protons, $\Lambda$ baryons, and $\Xi$ baryons) are measured in pp collisions at $\sqrt{s} = 13$ TeV with the ALICE detector to give insight into the particle production mechanisms and balancing of quantum numbers on the microscopic level. In particular, the distribution of strangeness is investigated in the correlations between the doubly-strange $\Xi$ baryon and mesons and baryons that contain a single strange quark, K and $\Lambda$. As a reference, the results are compared to $\Xi\pi$ and $\Xi\mathrm{p}$ correlations, where the associated mesons and baryons do not contain a strange valence quark. These measurements are expected to be sensitive to whether strangeness is produced through string breaking or in a thermal production scenario. Furthermore, the multiplicity dependence of the correlation functions is measured to look for the turn-on of additional particle production mechanisms with event activity. The results are compared to predictions from the string-breaking model PYTHIA 8, including tunes with baryon junctions and rope hadronisation enabled, the cluster hadronisation model HERWIG 7, and the core-corona model EPOS-LHC. While some aspects of the experimental data are described quantitatively or qualitatively by the Monte Carlo models, no one model can match all features of the data. These results provide stringent constraints on the strangeness and baryon number production mechanisms in pp collisions.

The production of the ψ(2S) charmonium state was measured with ALICE in Pb-Pb collisions at sqrt[s_{NN}]=5.02  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 ψ(2S) and J/ψ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region p_{T}<12  GeV/c. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio [σ^{ψ(2S)}/σ^{J/ψ}]_{Pb-Pb}/[σ^{ψ(2S)}/σ^{J/ψ}]_{pp}. It is found that in Pb-Pb collisions the ψ(2S) is suppressed by a factor of ∼2 with respect to the J/ψ. The ψ(2S) nuclear modification factor R_{AA} was also obtained as a function of both centrality and p_{T}. The results show that the ψ(2S) resonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up to ∼3 with respect to pp. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and of R_{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.

K+K- pairs may be produced in photonuclear collisions, either from the decays of photoproduced phi(1020) mesons or directly as nonresonant K+K- pairs. Measurements of K+K- photoproduction probe the couplings between the phi(1020) and charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction of K+K- pairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of direct K+K- production. There is significant KthornK- production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range 1.1 < M-KK < 1.4 GeV=c(2) above the phi(1020) resonance, for rapidity vertical bar y(KK)vertical bar < 0.8 and p(T,) (KK) < 0.1 GeV/c, the measured coherent photoproduction cross section is d sigma=dy = 3.37 +/- 0.61 (stat) +/- 0.15(syst) mb. The center-of-mass energy per nucleon of the photon-nucleus (Pb) systemW(gamma Pb,n) ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for phi(1020) photoproduction alone. The mass spectrum is fit to a cocktail consisting of phi (1020) decays, direct K+K- photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct K+K- photoproduction are presented.

Abstract Results on the transverse spherocity dependence of light-flavor particle production (π, K, p, ϕ, K*0, $$ {\textrm{K}}_{\textrm{S}}^0 $$ K S 0 , Λ, Ξ) at midrapidity in high-multiplicity pp collisions at $$ \sqrt{s} $$ s = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator $$ \left({S}_{\textrm{O}}^{p_{\textrm{T}}=1}\right) $$ S O p T = 1 categorizes events by their azimuthal topology. Utilizing narrow selections on $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 estimator is found to effectively constrain the hardness of the events when the midrapidity (|η| < 0.8) estimator is used.The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced.The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of $$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ S O p T = 1 .

The first measurements of $\mathrm{K^{*}(892)^{0}}$ resonance production as a function of charged-particle multiplicity in Xe$-$Xe collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.44 TeV and pp collisions at $\sqrt{s}=$ 5.02 TeV using the ALICE detector are presented. The resonance is reconstructed at midrapidity ($|y|<0.5$) using the hadronic decay channel $\mathrm{K^{*0}} \rightarrow \mathrm{K^{\pm} \pi^{\mp}}$. Measurements of transverse-momentum integrated yield, mean transverse-momentum, nuclear modification factor of $\mathrm{K^{*0}}$, and yield ratios of resonance to stable hadron ($\mathrm{K^{*0}}$/K) are compared across different collision systems (pp, p$-$Pb, Xe$-$Xe, and Pb$-$Pb) at similar collision energies to investigate how the production of $\mathrm{K^{*0}}$ resonances depends on the size of the system formed in these collisions. The hadronic rescattering effect is found to be independent of the size of colliding systems and mainly driven by the produced charged-particle multiplicity, which is a proxy of the volume of produced matter at the chemical freeze-out. In addition, the production yields of $\mathrm{K^{*0}}$ in Xe$-$Xe collisions are utilized to constrain the dependence of the kinetic freeze-out temperature on the system size using HRG-PCE model.

The production of ${K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}$ meson resonance is measured at midrapidity ($|y|<0.5$) in $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=5.02$ TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel ${K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}_{\mathrm{S}}^{0}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$. The transverse momentum distributions are obtained for various centrality intervals in the ${p}_{\mathrm{T}}$ range of $0.4\text{\ensuremath{-}}16 \mathrm{GeV}/c$. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for ${K}^{*}{(892)}^{0}$ within uncertainties. The ${p}_{\mathrm{T}}$-integrated yield ratio $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({K}^{+}+{K}^{\ensuremath{-}}$) in central $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions shows a significant suppression at a level of $9.3\ensuremath{\sigma}$ relative to $pp$ collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and music $+$ smash simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas music $+$ smash simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The ${p}_{\mathrm{T}}$-differential yield ratios $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({K}^{+}+{K}^{\ensuremath{-}}$) and $2\phantom{\rule{0.16em}{0ex}}{K}^{*}{(892)}^{\ifmmode\pm\else\textpm\fi{}}/({\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) are presented and compared with measurements in pp collisions at $\sqrt{s}=5.02$ TeV. Both particle ratios are found to be suppressed by up to a factor of five at ${p}_{\mathrm{T}}<2.0 \mathrm{GeV}/c$ in central $\mathrm{Pb}\text{\ensuremath{-}}\mathrm{Pb}$ collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (${R}_{\mathrm{AA}}$) shows a smooth evolution with centrality and is found to be below unity at ${p}_{\mathrm{T}}>8 \mathrm{GeV}/c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.

Charge-dependent two- and three-particle correlations measured in Xe-Xe collisions at root S-NN = 5.44 TeV are presented. Results are obtained for charged particles in the pseudorapidity range |eta| < 0.8 and transverse momentum interval 0.2 <= p(T) < 5.0 GeV/c for different collision centralities. The three-particle correlator gamma(alpha beta)=< cos(phi(alpha) +phi(beta) - 2 psi(2))>, calculated for different combinations of charge sign alpha and beta, is expected to be sensitive to the presence of the Chiral Magnetic Effect (CME). Its magnitude is similar to the one observed in Pb-Pb collisions in contrast to a smaller CME signal in Xe-Xe collisions than in Pb-Pb collisions predicted by Monte Carlo (MC) calculations including a magnetic field induced by the spectator protons. These observations point to a large nonCME contribution to the correlator. Furthermore, the charge dependence of gamma(alpha beta) can be described by a blast wave model calculation that incorporates background effects and by the Anomalous Viscous Fluid Dynamics model with values of the CME signal consistent with zero. The Xe-Xe and Pb-Pb results are combined with the expected CME signal dependence on the system size from the MC calculations including a magnetic field to obtain the fraction of CME contribution in gamma(alpha beta), f(CME). The CME fraction is compatible with zero for the 30% most central events in both systems and then becomes positive. This yields an upper limit of 2% (3%) and 25% (32%) at 95% (99.7%) confidence level for the CME signal contribution to gamma(alpha beta) in the 0-70% Xe-Xe and Pb-Pb collisions, respectively.

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high p(T)) charged hadron, in pp and central Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision root s(NN) = 5.02 TeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range in p(T,ch jet) and jet resolution parameter R. Recoil jet yields are reported for R = 0.2, 0.4, and 0.5 in the range 7 < p(T,ch jet) < 140 GeV/c and pi/2 < Delta phi < pi, where Delta phi is the azimuthal angular separation between hadron trigger and recoil jet. The low-p(T,ch jet) reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark-gluon plasma generated in high-energy nuclear collisions. Comparison of p(T,ch jet) distributions from pp and central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.

The production of K*(892)(+/-) meson resonance is measured at midrapidity (|y| < 0.5) in Pb-Pb collisions at root s(NN) = 5.02 TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel K *( 892)(+/-) -> K-S(0)pi(+/-). The transverse momentum distributions are obtained for various centrality intervals in the p(T) range of 0.4-16 GeV/c. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for K *(892)(0) within uncertainties. The p(T)-integrated yield ratio 2 K*(892)(+/-)/(K+ + K-) in central Pb-Pb collisions shows a significant suppression at a level of 9.3 sigma relative to pp collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and MUSIC + SMASH simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC + SMASH simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The p(T)-differential yield ratios 2 K*(892)(+/-)/(K+ + K-) and 2 K *(892)(+/-) /( pi(+) + pi(-)) are presented and compared with measurements in pp collisions at root s = 5.02 TeV. Both particle ratios are found to be suppressed by up to a factor of five at p(T) < 2.0 GeV/c in central Pb-Pb collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (R-AA) shows a smooth evolution with centrality and is found to be below unity at p(T) > 8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.

Luminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb$-$Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan. This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be $7.67 \pm 0.25$ b, in agreement with predictions using the Glauber model.

In this letter, measurements of (anti)alpha production in central (0–10%) Pb–Pb collisions at a center-of-mass energy per nucleon–nucleon pair of sNN = 5.02 TeV are presented, including the first measurement of an antialpha transverse-momentum spectrum. Owing to its large mass, the production of (anti)alpha is expected to be sensitive to different particle production models. The production yields and transverse-momentum spectra of nuclei are of particular interest because they provide a stringent test of these models. The averaged antialpha and alpha spectrum is compared to the spectra of lighter particles, by including it into a common blast-wave fit capturing the hydrodynamic-like flow of all particles. This fit is indicating that the (anti)alpha also participates in the collective expansion of the medium created in the collision. A blast-wave fit including only protons, (anti)alpha, and other light nuclei results in a similar flow velocity as the fit that includes all particles. A similar flow velocity, but a significantly larger kinetic freeze-out temperature is obtained when only protons and light nuclei are included in the fit. The coalescence parameter B4 is well described by calculations from a statistical hadronization model but significantly underestimated by calculations assuming nucleus formation via coalescence of nucleons. Similarly, the (anti)alpha-to-proton ratio is well described by the statistical hadronization model. On the other hand, coalescence calculations including approaches with different implementations of the (anti)alpha substructure tend to underestimate the data.