The ALICE Collaboration presents a new suite of jet substructure measurements in Pb–Pb and pp collisions at a center-of-mass energy per nucleon pair sNN=5.02 Image 1. These measurements provide access to the internal structure of jets via the momentum and angle of their constituents, probing how the quark–gluon plasma modifies jets, an effect known as jet quenching. Jet grooming additionally removes soft wide-angle radiation to enhance perturbative accuracy and reduce experimental uncertainties. We report the groomed and ungroomed jet mass mjet and jet angularities λακ using κ=1 and α>0. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameter R=0.2. A narrowing of the jet mass and angularity distributions in Pb–Pb collisions with respect to pp is observed and is enhanced for groomed results, confirming modification of the jet core. By using consistent jet definitions and kinematic cuts between the mass and angularities for the first time, previous inconsistencies in the interpretation of quenching measurements are resolved, rectifying a hurdle for understanding how jet quenching arises from first principles and highlighting the importance of a well-controlled baseline. These results are compared with a variety of theoretical models of jet quenching, providing constraints on jet energy-loss mechanisms in the quark–gluon plasma.

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 Ξ^{-} and Ξ[over ¯]^{+} 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_{NN}]=5.02  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.

The pT-differential cross section of ω meson production in pp collisions at √(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 < pT < 50 GeV/c. The meson is reconstructed via the ω → π+π−π0 decay channel. The results are compared with various theoretical calculations: PYTHIA8.2 with the Monash 2013 tune overestimates the data by up to 50

The production yields of antideuterons and antiprotons are measured in pp collisions at a center-of-mass energy of root s = 13 TeV, as a function of transverse momentum (p(T)) and rapidity (y), for the first time rapidity-differentially up to vertical bar y vertical bar = 0.7. The measured spectra are used to study the p(T) and rapidity dependence of the coalescence parameter B-2, which quantifies the coalescence probability of antideuterons. The p(T) and rapidity dependence of the obtained B-2 is extrapolated for p(T) > 1.7 GeV/c and vertical bar y vertical bar > 0.7 using the phenomenological antideuteron production model implemented in PYTHIA 8.3 as well as a baryon coalescence afterburner model based on EPOS 3. Such measurements are of interest to the astrophysics community, since they can be used for the calculation of the flux of antinuclei from cosmic rays, in combination with coalescence models.

The first measurement of HΛ3 and H‾Λ‾3 differential production with respect to transverse momentum and centrality in Pb–Pb collisions at sNN=5.02 TeV is presented. The HΛ3 has been reconstructed via its two-charged-body decay channel, i.e., HΛ3→3He+π−. A Blast-Wave model fit of the pT-differential spectra of all nuclear species measured by the ALICE collaboration suggests that the HΛ3 kinetic freeze-out surface is consistent with that of other nuclei. The ratio between the integrated yields of HΛ3 and He3 is compared to predictions from the statistical hadronisation model and the coalescence model, with the latter being favoured by the presented measurements.

The inclusive production of the charm-strange baryon Ωc0 is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y|<0.8) in proton-proton (pp) collisions at the center-of-mass energy s=13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2<pT<12 GeV/c. The branching-fraction ratio BR(Ωc0→Ω−e+νe)/BR(Ωc0→Ω−π+) is measured to be 1.12±0.22 (stat) ±0.27 (syst). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented. © 2024 CERN, for the ALICE Collaboration 2024 CERN

The two-particle momentum correlation functions between charm mesons (D*± and D±) and charged light-flavor mesons (π± and K±) in all charge combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton–proton collisions at a center-of-mass energy of s=13 TeV. For DK and D*K pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of Dπ and D*π pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the Dπ and D*π systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero. © 2024 CERN, for the ALICE Collaboration 2024 CERN

Abstract The total charm-quark production cross section per unit of rapidity $$\textrm{d}\sigma ({{\textrm{c}}\overline{\textrm{c}}})/\textrm{d}y$$ d σ ( c c ¯ ) / d y , and the fragmentation fractions of charm quarks to different charm-hadron species $$f(\textrm{c}\rightarrow {\textrm{h}}_{\textrm{c}})$$ f ( c → h c ) , are measured for the first time in p–Pb collisions at $$\sqrt{s_\textrm{NN}} = 5.02~\text {Te}\hspace{-1.00006pt}\textrm{V} $$ s NN = 5.02 Te 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}$$ D 0 , $$\textrm{D}^{+}$$ D + , $$\textrm{D}_\textrm{s}^{+}$$ D s + , and $$\mathrm {J/\psi }$$ J / ψ mesons, and $$\Lambda _\textrm{c}^{+}$$ Λ c + and $$\Xi _\textrm{c}^{0}$$ Ξ c 0 baryons. The resulting cross section is $$ \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} $$ d σ ( c c ¯ ) / d y = 219.6 ± 6.3 ( stat . ) - 11.8 + 10.5 ( syst . ) - 2.9 + 8.3 ( extr . ) ± 5.4 ( BR ) ± 4.6 ( lumi . ) ± 19.5 ( rapidity shape ) + 15.0 ( Ω c 0 ) mb , which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at $$\sqrt{s} = 5.02$$ s = 5.02 and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with $$\mathrm {e^{+}e^{-}}$$ e + e - and $$\mathrm {e^{-}p}$$ e - p collisions. The $$p_\textrm{T}$$ p T -integrated nuclear modification factor of charm quarks, $$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 pPb ( c c ¯ ) = 0.91 ± 0.04 ( stat . ) - 0.09 + 0.08 ( syst . ) - 0.03 + 0.05 ( extr . ) ± 0.03 ( lumi . ) , is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions.

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 inclusive production of the charm-strange baryon Omega(0)(c) is measured for the first time via its semileptonic decay into Omega(-)e(+)nu(e) at midrapidity (vertical bar y vertical bar < 0.8) in proton-proton (pp) collisions at the center-of-mass energy root s =13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < p(T) < 12 GeV=c. The branching-fraction ratio BR(Omega(0)(c) -> Omega(-)e(+)nu(e))/BR(Omega(0)(c) -> Omega(-)pi(+)) is measured to be 1.12 +/- 0.22 (stat) +/- 0.27 (syst). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented.

Measurements of the pT-dependent flow vector fluctuations in Pb–Pb collisions at sNN=5.02TeV using azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [ALICE Collaboration, ] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the pT-dependent flow vector fluctuations at sNN=5.02TeV with two-particle correlations. Significant pT-dependent fluctuations of the V⃗2 flow vector in Pb–Pb collisions are found across different centrality ranges, with the largest fluctuations of up to ∼15% being present in the 5% most central collisions. In parallel, no evidence of significant pT-dependent fluctuations of V⃗3 or V⃗4 is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than 5σ significance in central collisions. These observations in Pb–Pb collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high pT, which might be biased by pT-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be reexamined to improve our understanding of initial conditions, quark–gluon plasma properties, and the dynamic evolution of the created system. ©2024 CERN, for the ALICE Collaboration 2024 CERN

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.

AbstractThe first measurement of the multiplicity dependence of intra-jet properties of leading charged-particle jets in proton–proton (pp) collisions is reported. The mean charged-particle multiplicity and jet fragmentation distributions are measured in minimum-bias and high-multiplicity pp collisions at center-of-mass energy $$\sqrt{s}$$ s = 13 TeV using the ALICE detector. Jets are reconstructed from charged particles produced in the midrapidity region ($$|\eta | < 0.9$$ | η | < 0.9 ) using the sequential recombination anti-$$k_{\textrm{T}}$$ k T algorithm with jet resolution parameters R = 0.2, 0.3, and 0.4 for the transverse momentum ($$p_\textrm{T}$$ p T ) interval 5–110 GeV/c. The high-multiplicity events are selected by the forward V0 scintillator detectors. The mean charged-particle multiplicity inside the leading jet cone rises monotonically with increasing jet $$p_\textrm{T}$$ p T in qualitative agreement with previous measurements at lower energies. The distributions of jet fragmentation function variables $$z^{\textrm{ch}}$$ z ch and $$\xi ^{\textrm{ch}}$$ ξ ch are measured for different jet-$$p_\textrm{T}$$ p T intervals. Jet-$$p_\textrm{T}$$ p T independent fragmentation of leading jets is observed for wider jets except at high- and low-$$z^{\textrm{ch}}$$ z ch values. The observed “hump-backed plateau” structure in the $$\xi ^{\textrm{ch}}$$ ξ ch distribution indicates suppression of low-$$p_\textrm{T}$$ p T particles. In high-multiplicity events, an enhancement of the fragmentation probability of low-$$z^{\textrm{ch}}$$ z ch particles accompanied by a suppression of high-$$z^{\textrm{ch}}$$ z ch particles is observed compared to minimum-bias events. This behavior becomes more prominent for low-$$p_\textrm{T}$$ p T jets with larger jet radius. The results are compared with predictions of QCD-inspired event generators, PYTHIA 8 with Monash 2013 tune and EPOS LHC. It is found that PYTHIA 8 qualitatively reproduces the jet modification in high-multiplicity events except at high jet $$p_\textrm{T}$$ p T . These measurements provide important constraints to models of jet fragmentation.

This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced rho(0) mesons. The rho(0) mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the cos(2 phi) modulation, where phi is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb-Pb collisions at a center-of-mass energy of root s(NN) = 5.02 TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the cos(2 phi) modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured cos(2 phi) anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.

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.

The first measurements of femtoscopic correlations with the particle pair combinations pi +/- K-S(0) in pp collisions at root s = 13 TeV at the Large Hadron Collider (LHC) are reported by the ALICE experiment. Using the femtoscopic approach, it is shown that it is possible to study the elusive K-0*(700) particle that has been considered a tetraquark candidate for over forty years. Source and final-state interaction parameters are extracted by fitting a model assuming a Gaussian source to the experimentally measured two-particle correlation functions. The final-state interaction in the pi +/- K-S(0) system is modeled through a resonant scattering amplitude, defined in terms of a mass and a coupling parameter, The extracted mass and Breit-Wigner width, derived from the coupling parameter, of the final-state interaction are found to be consistent with previous measurements of the K-0*(700). The small value and increase of the correlation strength with increasing source size support the hypothesis that the K-0*(700) is a four-quark state, i.e. a tetraquark state of the form (q(1), (q(2)) over bar, q(3), (q(3)) over bar) in which q(1), q(2) and q(3) indicate the flavor of the valence quarks of the pi and K-S(0). This latter trend is also confirmed via a simple geometric model that assumes a tetraquark structure of the K-0*(700) resonance.

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.

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 .

This Letter presents the measurement of near-side associated per-trigger yields, denoted ridge yields, from the analysis of angular correlations of charged hadrons in proton-proton collisions at sqrt[s]=13  TeV. Long-range ridge yields are extracted for pairs of charged particles with a pseudorapidity difference of 1.4<|Δη|<1.8 and a transverse momentum of 1<p_{T}<2  GeV/c, as a function of the charged-particle multiplicity measured at midrapidity. This Letter extends the measurements of the ridge yield to the low multiplicity region, where in hadronic collisions it is typically conjectured that a strongly interacting medium is unlikely to be formed. The precision of the new low multiplicity results allows for the first direct quantitative comparison with the results obtained in e^{+}e^{-} collisions at sqrt[s]=91  GeV and sqrt[s]=183-209  GeV, where initial-state effects such as preequilibrium dynamics and collision geometry are not expected to play a role. In the multiplicity range 8≲⟨N_{ch}⟩≲24 where the e^{+}e^{-} results have good precision, the measured ridge yields in pp collisions are substantially larger than the limits set in e^{+}e^{-} annihilations. Consequently, the findings presented in this Letter suggest that the processes involved in e^{+}e^{-} annihilations do not contribute significantly to the emergence of long-range correlations in pp collisions.