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This paper presents the first measurement of the angle between different jet axes (denoted as $\mathrm{\Delta }{R}_{\mathrm{axis}}$ ) in $\text{Pb-Pb}$ collisions. The measurement is carried out in the 0–10 % most-central events at $\sqrt{s_{NN}}=5.02$ TeV. Jets are assembled by clustering charged particles at midrapidity using the $\text{anti-}{k}_{\mathrm{T}}$ algorithm with resolution parameters $R=0.2$ and 0.4 and transverse momenta in the intervals $40<p_{\mathrm{T}}^{\mathrm{ch}\mathrm{jet}}<140\mathrm{GeV}/c$ and $80<p_{\mathrm{T}}^{\mathrm{ch}\mathrm{jet}}<140\mathrm{GeV}/c$ , respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the $\text{Pb-Pb}$ distribution relative to $\mathit{pp}$ can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet $p_{\mathrm{T}}$ broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of $\text{Pb-Pb}$ and $\mathit{pp}$ collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss. 

The first measurement of the $e^{+}{e}^{-}$ pair production at midrapidity and low invariant mass in central Pb-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ at the Large Hadron Collider is presented. The yield of $e^{+}{e}^{-}$ pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass ( $m_{ee}$ ) and pair transverse momentum ( $p_{\mathrm{T},ee}$ ) ranges $m_{ee}<3.5\mathrm{GeV}/c^2$ and $p_{\mathrm{T},ee}<8\mathrm{GeV}/c$ . For $0.18<m_{ee}<0.5\mathrm{GeV}/c^2$ the ratio of data to the cocktail of hadronic contributions amounts to $1.40\pm 0.11\left(\mathrm{stat}.\right)\pm 0.23\left(\mathrm{syst}.\right)\pm 0.16\left(\mathrm{cocktail}\right)$ and $1.42\pm 0.11\left(\mathrm{stat}.\right)\pm 0.23{\left(\mathrm{syst}.\right)}_{-0.29}^{+0.24}\left(\mathrm{cocktail}\right)$ , including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal $e^{+}{e}^{-}$ pairs from the hadronic and partonic phases. In the intermediate-mass range ( $1.2<m_{ee}<2.6\mathrm{GeV}/c^2$ ), the pair transverse impact parameter of the $e^{+}{e}^{-}$ pairs ( ${\mathrm{DCA}}_{ee}$ , where “DCA” denotes “distance of closest approach”) is used for the first time in Pb-Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of $e^{+}{e}^{-}$ pairs from $c\overline{c}$ and an additional prompt component. Finally, the first direct-photon measurement in the 10% most central Pb-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ is reported via the study of virtual direct photons in the transverse momentum range $1<p_{\mathrm{T}}<5\mathrm{GeV}/c$ . A model including prompt photons, as well as photons from the preequilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties. 

A<sc>bstract</sc> Thep_T-differential cross section ofωmeson production in pp collisions at$$ \sqrt{s} $$ $\sqrt{s}$ = 13 TeV at midrapidity (|y| <0.5) was measured with the ALICE detector at the LHC, covering an unprecedented transverse-momentum range of 1.6< p_T<50 GeV/c. The meson is reconstructed via theω→π⁺π⁻π⁰decay channel. The results are compared with various theoretical calculations: PYTHIA8.2 with the Monash 2013 tune overestimates the data by up to 50%, whereas good agreement is observed with Next-to-Leading Order (NLO) calculations incorporatingωfragmentation using a broken SU(3) model. Theω/π⁰ratio is presented and compared with theoretical calculations and the available measurements at lower collision energies. The presented data triples thep_Tranges of previously available measurements. A constant ratio ofC^ω/π0= 0.578 ± 0.006 (stat.) ± 0.013 (syst.) is found above a transverse momentum of 4 GeV/c, which is in agreement with previous findings at lower collision energies within the systematic and statistical uncertainties. 

Abstract The femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose–Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at$$\sqrt{s}~=~13$$ $\sqrt{s}=13$  TeV from charged$$\uppi $$ $\pi$ –$$\uppi $$ $\pi$ correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of$$\textrm{K}$$ $\text{K}$ –$$\textrm{p}$$ $\text{p}$  pairs. The size of the primordial source is evaluated as a function of the transverse mass ($$m_{\textrm{T}}$$ $m_{\text{T}}$ ) of the pairs, leading to the observation of a common scaling for both$$\uppi $$ $\pi$ –$$\uppi $$ $\pi$ and$$\textrm{K}$$ $\text{K}$ –$$\textrm{p}$$ $\text{p}$  , suggesting a collective effect. Further, the present results are compatible with the$$m_{\textrm{T}}$$ $m_{\text{T}}$ scaling of the$$\textrm{p}$$ $\text{p}$ –$$\textrm{p}$$ $\text{p}$  and p$$-\Lambda $$ $-\Lambda$ primordial source measured by ALICE in high multiplicity pp collisions, providing additional evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron–hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles. 

Abstract The transverse momentum ($$p_{\textrm{T}}$$ $p_{\text{T}}$ ) differential production cross section of the promptly produced charm-strange baryon$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$ (and its charge conjugate$$\overline{\mathrm {\Xi _{c}^{0}}}$$ $\overline{{\Xi }_c^0}$ ) is measured at midrapidity via its hadronic decay into$$\mathrm{\pi ^{+}}\Xi ^{-}$$ ${\pi }^{+}{\Xi }^{-}$ in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision$$\sqrt{s_{\textrm{NN}}}~=~5.02$$ $\sqrt{s_{\text{NN}}}=5.02$  TeV with the ALICE detector at the LHC. The$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$ nuclear modification factor ($$R_{\textrm{pPb}}$$ $R_{\text{pPb}}$ ), calculated from the cross sections in pp and p–Pb collisions, is presented and compared with the$$R_{\textrm{pPb}}$$ $R_{\text{pPb}}$ of$$\mathrm {\Lambda _{c}^{+}}$$ ${\Lambda }_c^{+}$ baryons. The ratios between the$$p_{\textrm{T}}$$ $p_{\text{T}}$ -differential production cross section of$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$ baryons and those of$$\mathrm {D^0}$$ $D^0$ mesons and$$\mathrm {\Lambda _{c}^{+}}$$ ${\Lambda }_c^{+}$ baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt$$\Xi ^0_\textrm{c}$$ ${\Xi }_{\text{c}}^0$ baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p–Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model that includes string formation beyond leading-colour approximation or in which hadronisation is implemented via quark coalescence. The$$p_{\textrm{T}}$$ $p_{\text{T}}$ -integrated cross section of prompt$$\Xi ^0_\textrm{c}$$ ${\Xi }_{\text{c}}^0$ -baryon production at midrapidity extrapolated down to$$p_{\textrm{T}}$$ $p_{\text{T}}$ = 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p–Pb collisions at midrapidity. 

First measurements of hadron- $\mathrm{\Lambda }$ ( $h\text{−}\mathrm{\Lambda }$ ) azimuthal angular correlations in $p$ -Pb collisions at $\sqrt{s_{NN}} =5.02$  TeV using the ALICE detector at the Large Hadron Collider are presented. These correlations are used to separate the production of associated $\mathrm{\Lambda }$ baryons into three different kinematic regions, namely those produced in the direction of the trigger particle (near side), those produced in the opposite direction (away side), and those whose production is uncorrelated with the jet axis (underlying event). The per-trigger associated $\mathrm{\Lambda }$ yields in these regions are extracted, along with the near- and away-side azimuthal peak widths, and the results are studied as a function of associated particle $p_{\mathrm{T}}$ and event multiplicity. Comparisons with the event generator and previous measurements of the $\varphi \left(1020\right)$ meson are also made. The final results indicate that strangeness production in the highest multiplicity $p$ -Pb collisions is enhanced relative to low multiplicity collisions in both the jetlike regions and the underlying event. The production of $\mathrm{\Lambda }$ relative to charged hadrons is also enhanced in the underlying event when compared to the jetlike regions. Additionally, the results hint that strange quark production in the away-side of the jet is modified by soft interactions with the underlying event. ©2025 CERN, for the ALICE Collaboration2025CERN 

This Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons ${\mathrm{\Xi }}^{-}$ and ${\overline{\mathrm{\Xi }}}^{+}$ and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p-Pb, and Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ . The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data. © 2025 CERN, for the ALICE Collaboration2025CERN 

Abstract The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of$$\sqrt{s} =13$$ $\sqrt{s}=13$  TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of$$|\eta ^{\gamma }|<0.67$$ $|{\eta }^{\gamma }|<0.67$ and a transverse momentum range of$$7 $7<p_{\text{T}}^{\gamma }<200$ GeV/$$c$$ $c$ . The result extends to lower$$p_\textrm{T}^{\gamma }$$ $p_{\text{T}}^{\gamma }$ and$$x_\textrm{T}^{\gamma } = 2p_\textrm{T}^{\gamma }/\sqrt{s} $$ $x_{\text{T}}^{\gamma }=2p_{\text{T}}^{\gamma }/\sqrt{s}$ ranges, the lowest$$x_\textrm{T}^{\gamma }$$ $x_{\text{T}}^{\gamma }$ of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower$$p_\textrm{T}^{\gamma }$$ $p_{\text{T}}^{\gamma }$ at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties. 

Abstract The total charm-quark production cross section per unit of rapidity$$\textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y$$ $\text{d}\sigma \left(\text{c}\overline{\text{c}}\right)/\text{d}y$ , and the fragmentation fractions of charm quarks to different charm-hadron species$$f(\textrm{c}\rightarrow {\textrm{h}}_{\textrm{c}})$$ $f(\text{c}\to {\text{h}}_{\text{c}})$ , are measured for the first time in p–Pb collisions at$$\sqrt{s_\textrm{NN}} = 5.02~\text {Te}\hspace{-1.00006pt}\textrm{V} $$ $\sqrt{s_{\text{NN}}}=5.02\text{Te}\text{V}$ at midrapidity ($$-0.96 $-0.96<y<0.04$ in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species:$$\textrm{D}^{0}$$ ${\text{D}}^0$ ,$$\textrm{D}^{+}$$ ${\text{D}}^{+}$ ,$$\textrm{D}_\textrm{s}^{+}$$ ${\text{D}}_{\text{s}}^{+}$ , and$$\mathrm {J/\psi }$$ $J/\psi$ mesons, and$$\Lambda _\textrm{c}^{+}$$ ${\Lambda }_{\text{c}}^{+}$ and$$\Xi _\textrm{c}^{0}$$ ${\Xi }_{\text{c}}^0$ baryons. The resulting cross section is$$ \textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y =219.6 \pm 6.3\;(\mathrm {stat.}) {\;}_{-11.8}^{+10.5}\;(\mathrm {syst.}) {\;}_{-2.9}^{+8.3}\;(\mathrm {extr.})\pm 5.4\;(\textrm{BR})\pm 4.6\;(\mathrm {lumi.}) \pm 19.5\;(\text {rapidity shape})+15.0\;(\Omega _\textrm{c}^{0})\;\textrm{mb} $$ $\text{d}\sigma \left(\text{c}\overline{\text{c}}\right)/\text{d}y=219.6\pm 6.3\left(\mathrm{stat}.\right)_{-11.8}^{+10.5}\left(\mathrm{syst}.\right)_{-2.9}^{+8.3}\left(\mathrm{extr}.\right)\pm 5.4\left(\text{BR}\right)\pm 4.6\left(\mathrm{lumi}.\right)\pm 19.5\left(\text{rapidity shape}\right)+15.0\left({\Omega }_{\text{c}}^0\right)\text{mb}$ , which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at$$\sqrt{s} = 5.02$$ $\sqrt{s}=5.02$ and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with$$\mathrm {e^{+}e^{-}}$$ $e^{+}{e}^{-}$ and$$\mathrm {e^{-}p}$$ $e^{-}p$ collisions. The$$p_\textrm{T}$$ $p_{\text{T}}$ -integrated nuclear modification factor of charm quarks,$$R_\textrm{pPb}({\textrm{c}}\overline{\textrm{c}})= 0.91 \pm 0.04\;\mathrm{(stat.)} ^{+0.08}_{-0.09}\;\mathrm{(syst.)} ^{+0.05}_{-0.03}\;\mathrm{(extr.)} \pm 0.03\;\mathrm{(lumi.)}$$ $R_{\text{pPb}}\left(\text{c}\overline{\text{c}}\right)=0.91\pm 0.04{(\mathrm{stat}.)}_{-0.09}^{+0.08}{(\mathrm{syst}.)}_{-0.03}^{+0.05}(\mathrm{extr}.)\pm 0.03(\mathrm{lumi}.)$ , is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions. 

This work aims to differentiate strangeness produced from hard processes (jetlike) and softer processes (underlying event) by measuring the angular correlation between a high-momentum trigger hadron ( $h$ ) acting as a jet proxy and a produced strange hadron [ $\varphi \left(1020\right)$ meson]. Measuring $h\text{−}\varphi$ correlations at midrapidity in $p$ -Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ as a function of event multiplicity provides insight into the microscopic origin of strangeness enhancement in small collision systems. The jetlike and the underlying-event-like strangeness production are investigated as a function of event multiplicity. They are also compared between a lower and higher momentum region. The evolutions of the per-trigger yields within the near-side (aligned with the trigger hadron) and away-side (in the opposite direction of the trigger hadron) jets are studied separately, allowing for the characterization of two distinct jetlike production regimes. Furthermore, the $h\text{−}\varphi$ correlations within the underlying event give access to a production regime dominated by soft production processes, which can be compared directly to the in-jet production. Comparisons between $h\text{−}\varphi$ and dihadron correlations show that the observed strangeness enhancement is largely driven by the underlying event, where the $\varphi /h$ ratio is significantly larger than within the jet regions. As multiplicity increases, the fraction of the total $\varphi \left(1020\right)$ yield coming from jets decreases compared to the underlying event production, leading to high-multiplicity events being dominated by the increased strangeness production from the underlying event. ©2024 CERN, for the ALICE Collaboration2024CERN