Probing Strangeness Hadronization with Event-by-Event Production of Multistrange Hadrons.

The production of strange ( KS0 , Λ) and multi-strange (Ξ± and Ω±) hadrons in jets and underlying events in pp and p–Pb collisions is studied with ALICE at the LHC. Transverse momentum (p T) differential density distribution of particles produced in a jet is compared to that of inclusive particle production and that in underlying events. The particle yield ratios of (Λ+Λ¯)/2KS0 and (Ξ−+Ξ¯+)/(Λ+Λ¯) as a function of p T are also investigated in jets and underlying events. The production of the multi-strange hadrons, Ξ± and Ω±, and the corresponding ratio in jets and underlying events are measured for the first time. The p T-differential density distribution of hadrons associated with hard scattering decreases slower than that for inclusive production. The baryon-to-meson and baryon-to-baryon ratios measured in jets exhibit clear differences from values obtained from the inclusive spectra in the intermediate p T range. The p T distribution of strange hadrons produced in jets is also studied in pp collisions at s=13TeV and s=7TeV and in p–Pb collisions at sNN=5.02TeV . The p T spectra of particle produced in jets are independent of collision systems and collision energies. No apparent collision energy and collision system dependence is observed for the particle yield ratios of (Λ+Λ¯)/2KS0 and (Ξ−+Ξ¯+)/(Λ+Λ¯) associated with energetic jets. These new results are compared to PYTHIA 8 event generator. The (Λ+Λ¯)/2KS0 ratio are generally reproduced by the model, but large discrepancies between data and PYTHIA simulations are observed for (Ξ−+Ξ¯+)/(Λ+Λ¯) .

In this work, the relative Underlying event (UE) transverse multiplicity activity classifier (R_mathrm{{T}}) is used to study the strange and multi-strange hadron production in proton-proton collisions. Our study with R_mathrm{{T}} would allow to disentangle these particles, which are originating from the soft and hard QCD processes. We have used the PYTHIA 8 Monte-Carlo (MC) with a different implementation of color reconnection and rope hadronization models to demonstrate the proton-proton collisions data at sqrt{s}~= 13 TeV. The relative production of strange and multi-strange hadrons are discussed extensively in low and high transverse activity regions. In this contribution, the relative strange hadron production is enhanced with increasing R_mathrm{{T}}. This enhancement is significant for the strange baryons as compared to mesons. In addition, the particle ratios as a function of R_mathrm{{T}}~confirm the baryon enhancement in new Color Reconnection (newCR), whereas the Rope model confirms the baryon enhancement only with strange quark content. Experimental confirmation of such results will provide more insight into the soft physics in the transverse region, which will be useful to investigate various tunes based on hadronization and color reconnection schemes.

The production of strange and multi-strange hadrons in heavy-ion collisions is enhanced with respect to minimum bias proton-proton (pp) collisions. This feature has been further investigated by studying pp collisions as a function of the produced charged-particle multiplicity. In pp collisions, the strange hadron yields normalised to the pion yield show an increase with the multiplicity of produced particles. The origin of this striking phenomenon remains an open question: is it related to soft particle production or to hard scattering events, such as jets? The ALICE experiment has further studied this feature by separating strange hadrons produced in jets from those produced in soft processes. For this purpose, the angular correlation between high transverse momentum (${p_{\mathrm{T}}}$) charged particles and strange hadrons has been exploited. In this poster, the recent measurement of the near-side jet yield and the out-of-jet yield of $\mathrm{K^0_S}$ and $\Xi$ is shown as a function of the multiplicity of charged particles produced in pp collisions at $\sqrt{s}=13$ TeV. The ratio between the $\Xi$ and the $\mathrm{K^0_S}$ yields is also shown, to highlight the effect of the different strangeness content of the two hadrons. The results suggest that soft (out of jet) processes are the dominant contribution to strange particle production.

Charmonia are a valuable tool to investigate nuclear matter under extreme conditions, and particularly the strongly interacting medium formed in heavy-ion collisions. At the LHC energies, the regeneration process has been found to significantly impact the observed charmonium yields. In particular, the measurement of ψ(2S) production relative to J /ψ in Pb-Pb collisions has a strong discriminating power between different regeneration scenarios. Additionally, the study of quarkonium production in proton–proton (pp) collisions represents the reference for interpreting results obtained in Pb–Pb collisions and it is a key measurement to distinguish among the quarkonium production models in pp and p–Pb. In this contribution, preliminary findings on the ratio of ψ(2S)-to-J/ψ and inclusive J/ψ cross section in pp √ s = 13.6 TeV in Run 3, as well as published results about double ratio between Pb-Pb and pp collisions at 5.02 TeV and the inclusive J/ψ yield in pp collisions at √ s = 13 TeV and Pb–Pb collisions at √ s NN = 5.02 TeV in Run 2 measured by the ALICE Collaboration will be presented and compared with existing model calculations.

The production of {\Xi}$^{-}$ and {\Omega}$^{-}$ baryons and their anti-particles in pp, p-Pb and Pb-Pb collisions has been measured by the ALICE Collaboration. These hyperons are reconstructed via the detection of their charged weak-decay products, which are identified through their measured ionisation losses and momenta in the ALICE Time Projection Chamber. Comparing the production yields in Pb-Pb and pp collisions, a strangeness enhancement has been measured and found to increase with the centrality of the collision and with the strangeness content of the baryon; moreover, in the comparison with similar measurements at lower energies, it decreases as the centre-of-mass energy increases, following the trend already observed moving from SPS to RHIC. Recent measurement of cascade and {\Omega} in p-Pb interactions are compared with results in Pb-Pb and pp collisions and with predictions from thermal models, based on a grand canonical approach. The nuclear modification factors for the charged {\Xi} and {\Omega}, compared to the ones for the lighter particles, are also presented.

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The main objective of the ALICE experiment is to study the properties and the evolution of the high-energy density system created in relativistic heavy-ion collisions at the LHC. For that purpose, ALICE has unique particle identification capabilities that enable the detection of weakly-decaying particles in the high-multiplicity environment created in lead-lead (Pb-Pb) collisions.In this work, we discuss the systematic measurements of strange and multi-strange hadrons performed by ALICE for proton-proton (pp), proton-lead (p-Pb) and Pb-Pb collisions. Production rates measured for p-Pb and Pb-Pb are compared to predictions from statistical hadronization models and to measurements performed in pp collisions. These data are also used for a brief discussion on strangeness enhancement.

The results on the production of strange and multi-strange hadrons (K0S, Λ, Ξ and Ω) measured with ALICE in Pb-Pb collisions at the top LHC energy of [see formula in PDF] = 5.02 TeV are reported. Thanks to its excellent tracking and particle identification capabilities, ALICE is able to measure weakly decaying particles through the topological reconstruction of the identified hadronic decay products. Results are presented as a function of centrality and include transverse momentum spectra measured at central rapidity, pT-dependent Λ/K0S ratios and integrated yields. A systematic study of strangeness production is of fundamental importance for determining the thermal properties of the system created in ultrarelativistic heavy ion collisions. In order to study strangeness enhancement, the yields of studied particles are normalised to the corresponding measurement of pion production in the various centrality classes. The results are compared to measurements performed at lower energies, as well as to different systems and to predictions from statistical hadronization models.

The ALICE Collaboration has measured the inclusive J/ψ production at forward rapidity in pp, p-Pb and Pb-Pb collisions at the LHC. The pp measurements are crucial for a deeper understanding of the physics involving hadroproduction processes and provide the baseline for p-Pb and Pb-Pb measurements. The comparison of the results on the nuclear modification factor in p-Pb collisions as a function of rapidity or transverse momentum with theoretical predictions shows a fair agreement with a shadowing based model and energy loss models with or without a shadowing contribution. The nuclear modification factor in Pb-Pb as a function of collision centrality or transverse momentum shows a weaker suppression than at lower energies and can be described by statistical hadronization or transport models, suggesting a contribution to the J/ψ production due to the (re)combination of charm quarks, especially at low transverse momentum. The extrapolation to Pb-Pb collisions of the cold nuclear matter effects evaluated in p-Pb collisions supports the (re)combination mechanism interpretation.

We present ALICE results on strange and multi-strange hadron production as a function of centrality in Pb-Pb collisions at [Formula: see text] at the LHC. Their transverse momentum spectra, yields and particle ratios are compared to the corresponding measurements in pp collisions to address strangeness enhancement and high p T particle suppression. The results are also compared to measurements at RHIC and SPS energies.

The production of Ξ− and Ω− baryons and their anti-particles in Pb-Pb and pp collisions at = 2.76 TeV has been measured by the ALICE collaboration. The transverse momentum spectra at mid-rapidity (|y| < 0.5) in pp and in Pb-Pb collisions for five centrality intervals have been compared with model predictions. Hyperon yields and spectra in Pb-Pb collisions, normalized to the corresponding measurements in pp at the same centre-of-mass energy, allow the study of the strangeness enhancement and the nuclear modification factor as a function of the transverse momentum (pT) and collision centrality.

The ALICE Collaboration has studied inclusive $\\psi$(2S) production in pp, p-Pb and Pb-Pb collisions with the ALICE Muon Spectrometer which covers the rapidity range 2.5 $&lt;$ $y_{\\rm lab}$ $&lt;$ 4. The $\\psi$(2S) measurement was performed in the dimuon decay channel. The $\\psi$(2S) production cross-section and $\\psi$(2S) to J/$\\psi$ cross-section ratio in pp collisions will be presented, both integrated and differential in rapidity and in transverse momentum. In p-Pb collisions, $\\psi$(2S) results will be compared to the J/$\\psi$ ones by means of the production cross-section ratio and the double ratio [$\\psi$(2S)/J/$\\psi$]$_{{\\mathrm {pPb}}}$/[$\\psi$(2S)/J/$\\psi$]$_{{\\mathrm {pp}}}$ studied as a function of the resonance transverse momentum and event activity of the collision. The $\\psi$(2S) nuclear modification factor, $R_{{\\mathrm {pPb}}}$, will also be presented. Theoretical models based on nuclear shadowing, coherent energy loss or both cannot describe our results. Therefore other mechanisms must be invoked in order to describe the $\\psi$(2S) production. Finally, results on $\\psi$(2S) production in Pb-Pb collisions will be shown in two transverse momentum ranges as a function of centrality.

The ALICE Collaboration has studied the inclusive ψ(2S) meson production in pp, p-Pb and Pb-Pb collisions at the CERN LHC. The ψ(2S) is detected through its decay to a muon pair, using the forward Muon Spectrometer, which covers the pseudo-rapidity range –4 < η < -2.5. The ψ(2S) production cross sections in pp collisions are presented as a function of rapidity (y) and transverse momentum (pT). In p-Pb collisions, ψ(2S) results are compared to the J/ψ ones by the ratio of their production cross sections as a function of rapidity, transverse momentum and event activity. The ψ(2S) nuclear modification factor, RpA, is also discussed. The results show a ψ(2S) suppression compared to the one observed for the J/ψ meson and are not described by theoretical models including cold nuclear matter effects as nuclear shadowing and energy loss. Finally, the preliminary results of ψ(2S) meson production in Pb-Pb collisions are shown in two pT ranges as a function of the collision centrality.

We report results from the ALICE collaboration on jet production and jet properties in pp and Pb-Pb collisions at the LHC. The charged particle jet production cross-section and measurements of jet fragmentation and jet shape in pp collisions at = 7 TeV are presented. The results are confronted with simulations from Monte Carlo event generators. Measurements of charged particle jets in Pb-Pb collisions at = 2.76 TeV with resolution parameter R = 0.2 and R = 0.3 show a strong momentum dependent suppression in central relative to peripheral collisions. The analysis of the semi-inclusive distribution of charged particle jets recoiling from a high-pT trigger hadron allows an unbiased measurement of the jet structure for larger cone radii. No significant redistribution of the energy flow inside the jet cone is observed. Di-hadron correlations allow to assess jet structure at very low particle momenta. For 2 < pT,trig < 3 GeV/c and 1 < PT,assoc < 2 GeV/c, a strongly asymmetric near-side correlation, broader in Δη than Δϕ, is observed.

Identified particle spectra provide an important tool for understanding the particle production mechanism and the dynamical evolution of the medium created in relativistic heavy ion collisions. Studies involving strange and multi-strange hadrons, such as K0S, Λ, and Ξ−, carry additional information since there is no net strangeness content in the initial colliding system. Strangeness enhancement in AA collisions with respect to pp and pA collisions has long been considered as one of the signatures for quark-gluon plasma (QGP) formation. Recent observations of collective effects in high-multiplicity pp and pA collisions raise the question of whether QGP can also be formed in the smaller systems. Systematic studies of strange particle abundance, particle ratios, and nuclear modification factors can shed light on this issue. The CMS experiment has excellent strange-particle reconstruction capabilities over a broad kinematic range, and dedicated high-multiplicity triggers in pp and pPb collisions. The spectra of K0S, Λ, and Ξ− hadrons have been measured in various multiplicity and rapidity regions as a function of pT in pp, pPb, and PbPb collisions for several collision energies. The spectral shapes and particle ratios are compared in the different collision systems for events that have the same multiplicity and interpreted in the context of hydrodynamics models.