Centrality Intervals Research Articles

Collision energy dependence of elliptic flow of identified hadrons in heavy-ion collisions using the PHSD model

We report the first predictions of elliptic flow (v2) of identified hadrons at mid-rapidity (|y|< 1.0) in Au+Au collisions at Elab=6.7,8,11,and 25 A GeV using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (pT) dependence of identified hadron v2 in different centrality intervals (0-10%, 10-40%, and 40-80%) is shown. A clear centrality dependence of v2(pT) is observed for particles at Elab=6.7,8,11,and 25 A GeV. Within the PHSD model, the number of constituent quark (NCQ) scaling of v2 approximately follows in Au+Au collisions at all beam energies. A collision energy (sNN) dependence of π, K, and pv2 is studied in comparison with available published experimental data in the beam energy range of 6-25 A GeV. These predictions will help in interpreting the data from the forthcoming Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).

P T -spectra, nuclear modification factors (R AA , and R CP ) of (multi-) strange hadrons in Au+Au collisions at sNN= 200 GeV with HYDJET++

In this article, we have reported the transverse momentum (p T ) spectra and nuclear modification factors of (multi-) strange hadrons produced in Au+Au collisions at sNN= 200 GeV using the Monte Carlo HYDJET++ model. For the present study, we have tuned few of the input parameters, in both soft as well as hard parts, of the model to appropriately describe the production of (multi-) strange hadrons. We have presented the p T -spectra of (multi-) strange hadrons in different centrality intervals. On comparing p T -spectra with the experimental data, we observe that the model does not achieve thermal equilibrium for kaons toward peripheral collisions and for omega baryons for all the centrality intervals. The R AA results obtained by the model reproduce the experimental data well while the R CP results show less suppression at higher p T than the experimental data. Further, HYDJET++ results are also compared with different theoretical models and discussed, wherever possible.

Bulk properties of the system in Au–Au collisions at 3 GeV and their dependence on collision centrality and particle rapidity

We analyze the transverse momentum spectra of proton (p), deuteron (d), triton (t), and helium (3He and 4He) in different centrality intervals in various rapidity slices in gold–gold (Au–Au) collisions at sNN=3 GeV. We apply the blast-wave model with Tsallis statistics (TBW) to transverse momentum spectra of the particles, which fits well the data of STAR Collaboration. The freezeout parameters such as kinetic freezeout temperature, transverse flow velocity, and kinetic freezeout volume are extracted. Our findings reveal that central collisions exhibit higher values for the kinetic freezeout temperature, transverse flow velocity, and kinetic freezeout volume (which means that the central collisions are more hot and expansive), and observed that they decrease from central to peripheral collisions, and the former two parameters decrease from backward rapidity regions to mid-rapidity. This indicates a rapid expansion of the system in central collisions and in backward rapidities. The above parameters are mass-dependent, and the former increases, while the latter two decrease for heavier particles, reflecting the multiple kinetic freezeout and volume differential freezeout scenarios. Besides, the entropy parameter (q) is extracted, and it increases from peripheral to central and from backward to mid-rapidity regions.

Systematic study of flow vector fluctuations in sNN=5.02 TeV Pb-Pb collisions

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

Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02TeV Pb+Pb and pp Collisions with the ATLAS Detector.

Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy quarks produced in 5.02TeV Pb+Pb and pp collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying p_{T}^{μ}>4 GeV and |η^{μ}|<2.4, respectively. The distributions of azimuthal angle separation Δϕ for muon pairs having pseudorapidity separation |Δη|>0.8, are measured in different Pb+Pb centrality intervals and compared to the same distribution measured in pp collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all Δϕ distributions at Δϕ∼π, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the Δϕ distributions, are found to not vary significantly as a function of Pb+Pb collision centrality and are similar for pp and Pb+Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma.

Probing the magnetic field strength dependence of the chiral magnetic effect

The article presents a study aimed at probing the dependence of the Chiral Magnetic Effect (CME) on the magnetic field strength using the Anomalous Viscous Fluid Dynamics (AVFD) model in Pb–Pb at LHC energies. The results demonstrate the quadratic dependence of the correlators used for the study of the CME in heavy ion collisions on the number of spectators, a proxy of the magnitude of the magnetic field. The article also presents the extension of this approach to a two dimensional space, formed by both the aforementioned proxy of the magnetic field strength but also a proxy of the final state ellipticity, a key ingredient of the background in these measurements, for each centrality interval. This provides an exciting possibility to experiments to isolate the background contributions from the potential CME signal.

Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb–Pb and Xe–Xe collisions

The pseudorapidity dependence of elliptic (v2), triangular (v3), and quadrangular (v4) flow coefficients of charged particles measured in Pb–Pb collisions at a centre-of-mass energy per nucleon pair of sNN=5.02TeV and in Xe–Xe collisions at sNN=5.44TeV with ALICE at the LHC are presented. The measurements are performed in the pseudorapidity range −3.5<η<5 for various centrality intervals using two- and multi-particle cumulants with the subevent method. The flow probability density function (p.d.f.) is studied with the ratio of flow coefficient v2 calculated with four- and two-particle cumulant, and suggests that the variance of flow p.d.f. is independent of pseudorapidity. The decorrelation of the flow vector in the longitudinal direction is probed using two-particle correlations. The results measured with respect to different reference regions in pseudorapidity exhibit differences, argued to be a result of saturating decorrelation effect above a certain pseudorapidity separation, in contrast to previous publications which assign this observation to non-flow effects. The results are compared to 3+1 dimensional hydrodynamic and the AMPT transport model calculations. Neither of the models is able to simultaneously describe the pseudorapidity dependence of measurements of anisotropic flow and its fluctuations. The results presented in this work highlight shortcomings in our current understanding of initial conditions and subsequent system expansion in the longitudinal direction. Therefore, they provide input for its improvement.

Probing the chiral magnetic wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC

The Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic (v2) and triangular (v3) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope r3Norm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {r}_3^{\ extrm{Norm}} $$\\end{document} is found to be larger than zero and to have a magnitude similar to r2Norm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {r}_2^{\ extrm{Norm}} $$\\end{document}, thus pointing to a large background contribution for these measurements. Furthermore, r2Norm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {r}_2^{\ extrm{Norm}} $$\\end{document} can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW (fCMW) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for fCMW, and in the 10–60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level.

Energy and system size dependence of strongly intensive fluctuation measures in heavy-ion collisions at FAIR energies

Event-by-event fluctuations of multiplicity and transverse momentum of charged hadrons produced in heavy-ion collisions at FAIR energies, 10A, 20A, 30A, and 40A GeV are studied in the framework of relativistic transport model, URQMD. Dependence of two families of strongly intensive measures of multiplicity(N) and transverse momentum (p T) fluctuations, Δ[p T, N] and Σ[p T, N], on collision centrality, centrality bin-widths and pseudorapidity windows are examined. Attempts are also made to study NN, N p T, and p T p T fluctuations using two window analysis method. The findings suggest that the measure, Δ[p T, N] be dealt with proper selection of centrality intervals. This measure also exhibits a strong dependence on the widths of η windows. The variable Σ[p T, N], however, is observed to be insensitive to the centrality bin-widths and shows a variation of <5% with the widths of η windows. The analysis of data after event mixing gives Δ[p T, N] and Σ[p T, N] values as ∼1 irrespective of the widths of η windows and collision centrality, as predicted by a model of independent particle emission, IPM. The study of joint fluctuations of the two quantities on two η windows separated in η space, reveals that Σ[N F, N B] values are ∼1 irrespective of the position of η windows whereas, the values of and firstly increase with η sep and later acquire saturations. The observed trend of centrality dependence of and agrees fairly well with those observed in MC simulated studies carried out for AA collisions at LHC energies in the framework model of string fusion.

Production of muons from heavy-flavour hadron decays in heavy-ion collisions with ALICE at the LHC

Measurements of the production of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4.0) in Pb–Pb collisions at and 5.02 TeV with the ALICE detector are presented along with the R AA measurements in different centrality intervals as a function of transverse momentum, p T. Results of the measured R AA at both energies are shown and are compared to the different model predictions.

Excitation Function of Freeze-Out Parameters in Symmetric Nucleus–Nucleus and Proton–Proton Collisions at the Same Collision Energy

We analyze the transverse momentum (pT) spectra of π+, π−, K+, K−, p, p¯, Λ, Λ¯, Ξ, Ξ¯, Ω−, Ω¯+ or Ω−+Ω¯+ in different centrality intervals in gold–gold (Au–Au) and lead–lead (Pb–Pb) symmetric collisions at 200 GeV and 2.76 TeV, respectively, by Tsallis–Pareto-type function. Proton–proton collisions at the same centre of mass energies are also analyzed for these particles to compare the results obtained from these systems. The present work extracts the effective temperature T, non-extensivity parameter (q), the mean transverse momentum spectra (⟨pT⟩), the multiplicity parameter (N0), kinetic freeze-out temperature (T0) and transverse flow velocity (βT). We reported a plateau structure of pT, T, T0, βT, pT and q in central collisions. Beyond the plateau region, the excitation function of all the above parameters decreases towards the periphery, except q, which has a reverse trend. The multiplicity parameter is also extracted, which is found to be decreasing towards the periphery from the central collisions. In addition, we observed that the excitation function of pp collisions is nearly the same to that of the most peripheral symmetric nucleus–nucleus collisions at the same colliding energy. Throughout the analyses, the same multiplicity parameters for particles and their antiparticles have been reported, which show the symmetric production of particles and their antiparticles.

Elliptic flow of identified hadrons in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the PHSD model

We present predictions of elliptic flow (v_2) of identified hadrons at mid-rapidity (|y| < 1.0) in Au+Au collisions at E_{lab} = 35~text {A}~text {GeV} using the Parton Hadron String Dynamics (PHSD) model. The transverse momentum (p_{textrm{T}}) dependence of identified hadron v_2 in minimum bias (0–80%) and three different centrality intervals (0–10%, 10–40%, and 40–80%) are presented. A clear centrality dependence of v_2(p_{textrm{T}}) is observed for particles and anti-particles. We also present the p_{textrm{T}} dependence of v_2 difference ({Delta } v_2) between particles and corresponding anti-particles. A significant difference in v_2 values for baryons and anti-baryons is observed. Constituent quark scaling (NCQ) of v_{2} is investigated in Au+Au collisions. We also present a v_2(p_{textrm{T}}) ratio between the HSD and PHSD modes to explore the effect of hadronic and partonic interactions in the medium. These predictions are useful for interpreting the data measured in the Beam Energy Scan (BES) program at RHIC. They will also be useful for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) and Multi-Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA).

Anisotropic flow and flow fluctuations of identified hadrons in Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV

The first measurements of elliptic flow of π±, K±, textrm{p}+overline{textrm{p}} , {textrm{K}}_{textrm{S}}^0 , Lambda +overline{Lambda} , ϕ, {Xi}^{-}+{overline{Xi}}^{+} , and {varOmega}^{-}+{overline{varOmega}}^{+} using multiparticle cumulants in Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV are resented. Results obtained with two- (v2{2}) and four-particle cumulants (v2{4}) are shown as a function of transverse momentum, pT, for various collision centrality intervals. Combining the data for both v2{2} and v2{4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous pT-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low pT and the approximate scaling with the number of constituent quarks at intermediate pT, are similarly present in the four-particle correlations and the combinations of v2{2} and v2{4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide pT range.

K*0 production in Au+Au collisions at sNN=7.7 , 11.5, 14.5, 19.6, 27, and 39 GeV from the RHIC beam energy scan

We report the measurement of $K^{*0}$ meson at midrapidity ($|y|<$ 1.0) in Au+Au collisions at $\sqrt{s_{\rm NN}}$~=~7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse momentum of $K^{*0}$ are presented as functions of collision centrality and beam energy. The $K^{*0}/K$ yield ratios are presented for different collision centrality intervals and beam energies. The $K^{*0}/K$ ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and p+p). The $K^{*0}/K$ ratio follows a similar centrality dependence to that observed in previous RHIC and LHC measurements. The data favor the scenario of the dominance of hadronic re-scattering over regeneration for $K^{*0}$ production in the hadronic phase of the medium.

Production and enhancement of (multi-) strange hadrons in Au+Au collisions at sNN=200 GeV RHIC energy and Pb+Pb collisions at sNN=2.76 TeV LHC energy

In this article, we investigate $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collision systems to understand the (multi-) strange hadron production at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies using the Monte Carlo $\mathrm{HYDJET}++$ model. We study the ${p}_{T}$ spectra, particle ratios, and strangeness enhancement factor for (multi-) strange hadrons. The ${p}_{T}$ spectra of ${K}^{+}({K}^{\ensuremath{-}})$, ${K}_{s}^{0}$, $\mathrm{\ensuremath{\Lambda}}(\overline{\mathrm{\ensuremath{\Lambda}}})$, ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Xi}}}}^{+})$, and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Omega}}}}^{+})$ are shown for both $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collision systems in various centrality intervals. We find that the strange quark thermalization might not be achieved by the model for multistrange baryons toward peripheral collisions. The ${p}_{T}$-differential particle ratios, focused on strange hadron-to-meson ratios, are reported for 0--5% and 40--60% centrality intervals for both the collision systems. We observe an enhancement in the particle ratios at intermediate ${p}_{T}$ region. ${p}_{T}$ integrated strange-to-nonstrange ratios suggest that chemical equilibrium might not be achieved for multistrange hadrons. We report the strangeness enhancement factor for $\mathrm{\ensuremath{\Lambda}}(\overline{\mathrm{\ensuremath{\Lambda}}})$, ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Xi}}}}^{+})$, and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}+{\overline{\mathrm{\ensuremath{\Omega}}}}^{+}$ at both RHIC and LHC energies. An increase in the enhancement factor is observed with the increase in strangeness content of the baryons. We also observe that enhancement is higher in $\mathrm{Au}+\mathrm{Au}$ collisions than in $\mathrm{Pb}+\mathrm{Pb}$ collisions. Further, we compare the $\mathrm{HYDJET}++$ results with the experimental data and various other simulation models, wherever possible.

Centrality and Transverse Spherocity Dependent Study of Charged-Particle Production in Xe–Xe Collisions at √SNN=5.44 TeV Using PYTHIA8 Angantyr and AMPT Models

Transverse spherocity is an event structure variable which provide an effective way to disentangle the data into hard and soft components of the processes corresponding to events with small and large numbers of multiparton interactions (MPI), respectively. Recent experimental results in small systems from the LHC suggest the importance of the transverse spherocity variable in the classification of the events. In this contribution, we have studied the dynamics of identified particle production in Xe–Xe collisions at √SNN = 5.44 TeV using A Multi-Phase Transport Model (AMPT) and the recently developed Angantyr model, which is incorporated within PYTHIA8. A study of the transverse momentum spectra of the identified particles is presented for soft (isotropic) and hard (jet-like) events in different centrality intervals.

Centrality Dependent Lévy Analysis of two-pion BEC Functions at PHENIX

We present most recent PHENIX preliminary data on centrality dependence of two-pion Bose-Einstein correlation functions measured in √SNN = 200 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The data are well described by assuming the source to be a Lévy-stable distribution. The Lévy parameters, R, α, λ are measured in 18 bins of transverse mass (mT) for 4 centrality intervals. The Lévy scale parameter R(mT) decreases with mT and exhibits a clear centrality ordering which supports its geometrical interpretation. The Lévy exponent α(mT) is independent of mT in every centrality bin but shows some centrality dependence. At all centralities α is significantly different from that of a Gaussian (α = 2) or Cauchy (α = 1) source distribution. The Lévy strength parameter λ was also investigated. We observed that λ(mT) decreases at low mT and saturates around mT = 0.6 GeV/c2. In the already published 0-30% centrality class, Monte Carlo simulations are found to be inconsistent with the measurements, unless a significant reduction of the in-medium mass of the η′ meson is included.

Study of Bulk Properties of Strange Particles in Au+Au Collisions at sNN = 54.4 GeV.

We analyzed the transverse momentum pT spectra of various strange hadrons KS0, Λ(Λ¯) and Ξ-(Ξ¯+) at mid-rapidity (y) in different centrality intervals from Au+Au collisions at sNN= 54.4 GeV. The pT spectra of these strange hadrons are investigated by the Tsallis-like distribution, which satisfactorily fits the experimental data. The bulk properties of the medium produced in ultra-relativistic heavy-ion collisions at the kinetic freeze-out are reflected by measuring the hadron spectra. The effective temperature T, transverse flow velocity βT, and mean pT along with other parameters that are strongly dependent on centrality and particle specie are extracted. The effective temperature of multi-strange particle (Ξ-(Ξ¯+)) is larger as compared to singly-strange particles Λ(Λ¯) and KS0. Furthermore, the kinetic freeze-out temperature T, transverse flow velocity βT. and mean pT (⟨pT⟩) show a decreasing trend towards lower centrality, while the entropy parameter q increases from central to peripheral collisions. In addition, a positive correlation of ⟨pT⟩ and T and a negative correlation of q and T are also reported.

Measurements of _{Λ}^{3}H and _{Λ}^{4}H Lifetimes and Yields in Au+Au Collisions in the High Baryon Density Region.

We report precision measurements of hypernuclei _{Λ}^{3}H and _{Λ}^{4}H lifetimes obtained from Au+Au collisions at sqrt[s_{NN}]=3.0 GeV and 7.2GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider, and the first measurement of _{Λ}^{3}H and _{Λ}^{4}H midrapidity yields in Au+Au collisions at sqrt[s_{NN}]=3.0 GeV. _{Λ}^{3}H and _{Λ}^{4}H, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221±15(stat)±19(syst) ps for _{Λ}^{3}H and 218±6(stat)±13(syst) ps for _{Λ}^{4}H. The p_{T}-integrated yields of _{Λ}^{3}H and _{Λ}^{4}H are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of _{Λ}^{4}H is different for 0%-10% and 10%-50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the _{Λ}^{3}H yield well, while underestimating the _{Λ}^{4}H yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured _{Λ}^{3}H and _{Λ}^{4}H yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.

Polarization of Λ and Λ[over ¯] Hyperons along the Beam Direction in Pb-Pb Collisions at sqrt[s]_{NN}=5.02 TeV.

The polarization of the Λ and Λ[over ¯] hyperons along the beam (z) direction, P_{z}, has been measured in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV recorded with ALICE at the Large Hadron Collider (LHC). The main contribution to P_{z} comes from elliptic flow-induced vorticity and can be characterized by the second Fourier sine coefficient P_{z,s2}=⟨P_{z}sin(2φ-2Ψ_{2})⟩, where φ is the hyperon azimuthal emission angle and Ψ_{2} is the elliptic flow plane angle. We report the measurement of P_{z,s2} for different collision centralities and in the 30%-50% centrality interval as a function of the hyperon transverse momentum and rapidity. The P_{z,s2} is positive similarly as measured by the STAR Collaboration in Au-Au collisions at sqrt[s_{NN}]=200 GeV, with somewhat smaller amplitude in the semicentral collisions. This is the first experimental evidence of a nonzero hyperon P_{z} in Pb-Pb collisions at the LHC. The comparison of the measured P_{z,s2} with the hydrodynamic model calculations shows sensitivity to the competing contributions from thermal and the recently found shear-induced vorticity, as well as to whether the polarization is acquired at the quark-gluon plasma or the hadronic phase.