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Abstract Quantum Chromodynamics predicts a phase transition from hadronic matter to quark–gluon plasma (QGP) at high temperatures and energy densities, where quarks and gluons (partons) are no longer confined within hadrons. The QGP forms in ultrarelativistic heavy-ion collisions. Anisotropic flow coefficients, quantifying the azimuthal expansion of produced matter, probe QGP properties. Flow measurements in high-energy heavy-ion collisions show a distinctive grouping of anisotropic flow for baryons and mesons at intermediate transverse momentum – a feature associated with flow imparted at the quark level, confirming QGP existence. The observation of QGP-like features in proton–proton and proton–ion collisions has sparked debate about QGP formation in smaller systems. For the first time, we demonstrate the distinctive grouping of anisotropic flow for baryons and mesons in high-multiplicity proton–lead and proton–proton collisions at the Large Hadron Collider (LHC). These results are described by a model including hydrodynamic flow followed by hadron formation via quark coalescence, consistent with the formation of partonic flowing systems in these collisions. 

A<sc>bstract</sc> The measurement of three-dimensional femtoscopic correlations between identical charged kaons (K^±K^±) produced in p–Pb collisions at center-of-mass energy per nucleon pair$$\sqrt{{s}_{\text{NN}}}=5.02$$TeV with ALICE at the LHC is presented for the first time. This measurement, supplementary to those in pp and Pb–Pb collisions, allows understanding the particle-production mechanisms at different charged-particle multiplicities and provides information on the dynamics of the source of particles created in p–Pb collisions, for which a general consensus does not yet exist. It is shown that the measured source sizes increase with charged-particle multiplicity and decrease with increasing pair transverse momentum. These trends for K^±K^±are similar to the ones observed earlier in identical charged-pion and$${\text{K}}_{\text{s}}^{0}{\text{K}}_{\text{s}}^{0}$$correlations in Pb–Pb collisions at various energies and inπ^±π^±correlations in p–Pb collisions at$$\sqrt{{s}_{\text{NN}}}=5.02$$TeV. At comparable multiplicity, the source sizes measured in p–Pb collisions agree within uncertainties with those observed in pp collisions, and there is an indication that they are smaller than those observed in Pb–Pb collisions. The obtained results are also compared with predictions from the hadronic interaction model EPOS 3, which tends to underestimate the source size for the most central collisions and agrees with the data for semicentral and peripheral events. Furthermore, the time of maximal emission for kaons is extracted. It turns out to be comparable with the value obtained in highly peripheral Pb–Pb collisions at the same energy, indicating that the kaon emission evolution is similar to that in p–Pb collisions. 

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. 

Abstract This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p–Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p–Pb collisions at centre-of-mass energies per nucleon pair of$$\sqrt{s_{\text {NN}}}={5.02}\,\textrm{TeV}$$ $\sqrt{s_{\text{NN}}}=5.02\text{TeV}$and 8.16 TeV, as well as in pp collisions at$$\sqrt{s}={5.02}\,\textrm{TeV}$$ $\sqrt{s}=5.02\text{TeV}$and 8 TeV. The cross section is obtained at midrapidity$$(|y|<0.7)$$ $\left(\right|y|<0.7)$using a charged-track based isolation momentum$$p_\textrm{T}^{\text {iso,~ch}}<{1.5}\,\textrm{GeV}/c$$ $p_{\text{T}}^{\text{iso, ch}}<1.5\text{GeV}/c$in a cone with radius$$R=0.4$$ $R=0.4$. The data for both collision systems are well reproduced by perturbative QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor$$R_{\text {pA}}$$ $R_{\text{pA}}$for both collision energies is consistent with unity for$$p_{\textrm{T}}$$ $p_{\text{T}}$$$>{20}\,\textrm{GeV}/c$$ $>20\text{GeV}/c$. However, deviations from unity ($$R_\textrm{pA}<1$$ $R_{\text{pA}}<1$) of up to 20% are observed for$$p_{\textrm{T}}$$ $p_{\text{T}}$$$<{20}\,\textrm{GeV}/c$$ $<20\text{GeV}/c$with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing$$p_{\textrm{T}}$$ $p_{\text{T}}$with a significance of$$2.3\upsigma $$ $2.3\sigma$for a non-zero slope and yields$$R_{\textrm{pA}}<1$$ $R_{\text{pA}}<1$with a significance of$$1.8\upsigma $$ $1.8\sigma$at$$\sqrt{s_{\textrm{NN}}}={8.16}\,\textrm{TeV}$$ $\sqrt{s_{\text{NN}}}=8.16\text{TeV}$for$$p_{\textrm{T}}$$ $p_{\text{T}}$$$<{20}\,\textrm{GeV}/c$$ $<20\text{GeV}/c$. In addition, a significance of$$1.1\upsigma $$ $1.1\sigma$is observed for$$R_{\textrm{pA}}<1$$ $R_{\text{pA}}<1$at the lower collision energy$$\sqrt{s_{\textrm{NN}}}={5.02}\,\textrm{TeV}$$ $\sqrt{s_{\text{NN}}}=5.02\text{TeV}$for$$p_{\textrm{T}} < {14}\,\textrm{GeV}/c$$ $p_{\text{T}}<14\text{GeV}/c$. The magnitude and shape of the suppression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus. 

Femtoscopy of nonidentical particle pairs has been instrumental for precision measurements of both two-particle sources and the final-state interactions in high-energy elementary and heavy-ion collisions. The majority of measurements assessing the source properties are based on identical particle pairs, providing direct access to the characteristics of the single-particle source. The work in this paper demonstrates, via femtoscopy measurements of charged pion-deuteron pairs in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$TeV, the feasibility of accessing the characteristics of the single-particle femtoscopic source by using particle pairs with large mass differences such as pions and deuterons. The first experimental results of the measurement of deuteron source sizes in ultrarelativistic heavy-ion collisions are presented. The results show good agreement with the trend derived from other charged hadrons such as pions, kaons, and protons as a function of transverse mass, indicating similar source properties. 

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> The first measurement of prompt D^*+-meson spin alignment in ultrarelativistic heavy-ion collisions with respect to the direction orthogonal to the reaction plane is presented. The spin alignment is quantified by measuring the elementρ₀₀of the diagonal spin-density matrix for prompt D^*+mesons with 4< p_T<30 GeV/cin two rapidity intervals, |y|<0.3 and 0.3<|y|<0.8, in central (0–10%) and midcentral (30–50%) Pb–Pb collisions at$$\sqrt{{s}_{\text{NN}}}={5}.0{2}$$TeV. Evidence of spin alignmentρ₀₀>1/3 has been found forp_T>15 GeV/cand 0.3<|y|<0.8 with a significance of 3.1σ. The measured spin alignment of prompt D^*+mesons is compared with the one of inclusive J/ψ mesons measured at forward rapidity (2.5< y <4). 

We present the measurement of the $p_{\mathrm{T}}$-differential production cross section of $\omega$mesons in and $p$-Pb collisions at $\sqrt{s_{NN}}=5.02$TeV at midrapidity by ALICE. In addition, the first measurement of the nuclear modification factor $R_{p\mathrm{Pb}}$for $\omega$mesons at LHC energies is presented, complementing the existing measurements of lighter neutral mesons such as the ${\pi }^0$and $\eta$. Within the measured $p_{\mathrm{T}}$range, the $R_{p\mathrm{Pb}}$of $\omega$mesons is compatible with no cold nuclear matter effects within the uncertainties, consistent with previous measurements at lower energies. The $\omega /{\pi }^0$ratio is presented for both collision systems, showing no collision system dependence within the uncertainties. The comparison to previously published $\omega /{\pi }^0$ratios at lower and higher collision energies in collisions suggests a decreasing trend of the ratio above $p_{\mathrm{T}}$= 4 GeV/ $c$with increasing collision energy. The data in both collision systems are compared to predictions from PYTHIA 8, EPOS LHC, and DPMJET event generators, revealing significant shortcomings in these models’ ability to describe the production of $\omega$mesons.