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Item type:Publication, Systematic study of flow vector fluctuations in √sNN = 5.02 TeV Pb–Pb collisions(American Physical Society, 2024-06-01)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, Phys. Rev. C 107, L051901 (2023)2469-998510.1103/PhysRevC.107.L051901] 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 V - 2 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 V - 3 or V - 4 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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, K*(892)± resonance production in Pb–Pb collisions at √sNN = 5.02 TeV(American Physical Society, 2024-04-01)The production of K∗(892)± meson resonance is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at sNN=5.02 TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel K∗(892)±→KS0π±. The transverse momentum distributions are obtained for various centrality intervals in the pT range of 0.4-16 GeV/c. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for K∗(892)0 within uncertainties. The pT-integrated yield ratio 2K∗(892)±/(K++K-) in central Pb-Pb collisions shows a significant suppression at a level of 9.3σ relative to pp collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and music + smash simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas music + smash simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The pT-differential yield ratios 2K∗(892)±/(K++K-) and 2K∗(892)±/(π++π-) are presented and compared with measurements in pp collisions at s=5.02 TeV. Both particle ratios are found to be suppressed by up to a factor of five at pT<2.0 GeV/c in central Pb-Pb collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (RAA) shows a smooth evolution with centrality and is found to be below unity at pT>8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, System-size dependence of the hadronic rescattering effect at energies available at the CERN Large Hadron Collider(American Physical Society, 2024-01-01)The first measurements of K∗(892)0 resonance production as a function of charged-particle multiplicity in Xe-Xe collisions at sNN=5.44 TeV and pp collisions ats=5.02 TeV using the ALICE detector are presented. The resonance is reconstructed at midrapidity (|y| < 0.5) using the hadronic decay channel K∗0 →K±π∓. Measurements of transverse-momentum integrated yield, mean transverse-momentum, nuclear modification factor of K∗0, and yield ratios of resonance to stable hadron (K∗0/K) are compared across different collision systems (pp, p-Pb, Xe-Xe, and Pb-Pb) at similar collision energies to investigate how the production of K∗0 resonances depends on the size of the system formed in these collisions. The hadronic rescattering effect is found to be independent of the size of colliding systems and mainly driven by the produced charged-particle multiplicity, which is a proxy of the volume of produced matter at the chemical freeze-out. In addition, the production yields of K∗0 in Xe-Xe collisions are utilized to constrain the dependence of the kinetic freeze-out temperature on the system size using the hadron resonance gas-partial chemical equilibrium model. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Observation of medium-induced yield enhancement and acoplanarity broadening of low-pT jets from measurements in pp and central Pb–Pb collisions at √sNN = 5.02 TeV(American Physical Society, 2024-07-12)The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high pT) hadron trigger in proton-proton and central Pb-Pb collisions at sNN=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<pT,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 pT 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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Emergence of long-range angular correlations in low-multiplicity proton-proton collisions(American Physical Society, 2024-04-26)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 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<pT<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 s=91 GeV and 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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, System-Size Dependence of the Charged-Particle Pseudorapidity Density at sNN = 5.02 TeV for pp, p–Pb, and Pb–Pb Collisions(Elsevier B.V., 2023-10-10)We present the first systematic comparison of the charged-particle pseudorapidity densities for three widely different collision systems, pp, p–Pb, and Pb–Pb, at the top energy of the Large Hadron Collider (sNN=5.02TeV) measured over a wide pseudorapidity range (−3.5<η<5), the widest possible among the four experiments at that facility. The systematic uncertainties are minimised since the measurements are recorded by the same experimental apparatus (ALICE). The distributions for p–Pb and Pb–Pb collisions are determined as a function of the centrality of the collisions, while results from pp collisions are reported for inelastic events with at least one charged particle at midrapidity. The charged-particle pseudorapidity densities are, under simple and robust assumptions, transformed to charged-particle rapidity densities. This allows for the calculation and the presentation of the evolution of the width of the rapidity distributions and of a lower bound on the Bjorken energy density, as a function of the number of participants in all three collision systems. We find a decreasing width of the particle production, and roughly a smooth ten fold increase in the energy density, as the system size grows, which is consistent with a gradually higher dense phase of matter. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Observation of Flow Angle and Flow Magnitude Fluctuations in Pb-Pb Collisions at sNN = 5.02 TeV at the CERN Large Hadron Collider(American Physical Society, 2023-05-01)This Letter reports on the first measurements of transverse momentum dependent flow angle ψn and flow magnitude vn fluctuations determined using new four-particle correlators. The measurements are performed for various centralities in Pb-Pb collisions at a center-of-mass energy per nucleon pair of sNN = 5.02 TeV with ALICE at the CERN Large Hadron Collider. Both flow angle and flow magnitude fluctuations are observed in the presented centrality ranges and are strongest in the most central collisions and for a transverse momentum pT>2GeV/c. Comparison with theoretical models, including iEBE-VISHNU, MUSIC, and AMPT, show that the measurements exhibit unique sensitivities to the initial state of heavy-ion collisions. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of Non-Prompt D-Meson Elliptic Flow in Pb–Pb Collisions at √sNN = 5.02 TeV(Institute for Ionics, 2023-12-01)The elliptic flow (v2) of D mesons from beauty-hadron decays (non-prompt D) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed at midrapidity (| y| < 0.8) from their hadronic decay D → K -π + , in the transverse momentum interval 2 < pT< 12 GeV/c. The result indicates a positive v2 for non-prompt D mesons with a significance of 2.7 σ . The non-prompt D -meson v2 is lower than that of prompt non-strange D mesons with 3.2 σ significance in 2<pT<8GeV/c , and compatible with the v2 of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of Electrons from Beauty-Hadron Decays in pp and Pb-Pb Collisions at sNN = 5.02 TeV(American Physical Society, 2023-09-01)The production of electrons from beauty-hadron decays was measured at midrapidity in proton-proton (pp) and central Pb-Pb collisions at center-of-mass energy per nucleon-nucleon pair sNN = 5.02 TeV, using the ALICE detector at the LHC. The cross section measured in pp collisions in the transverse momentum interval 2<pT<8GeV/c was compared with models based on perturbative quantum chromodynamics calculations. The yield in the 10% most central Pb-Pb collisions, measured in the interval 2<pT<26GeV/c, was used to compute the nuclear modification factor RAA, extrapolating the pp reference cross section to pT larger than 8 GeV/c. The measured RAA shows significant suppression of the yield of electrons from beauty-hadron decays at high pT and does not show a significant dependence above 8GeV/c within uncertainties. The results are described by several theoretical models based on different implementations of the interaction of heavy quarks with a quark-gluon plasma, which predict a smaller energy loss for beauty quarks compared to light and charm quarks. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Jet-Like Correlations with Respect to KS0 and Λ (Λ̄) in pp and Central Pb–Pb Collisions at √sNN = 5.02 TeV(Springer Nature, 2023-06-01)Two-particle correlations with KS0 , Λ / Λ ¯ , and charged hadrons as trigger particles in the transverse momentum range 8 < pT , trig< 16 GeV/ c , and associated charged particles within 1 < pT , assoc< 8 GeV/ c , are studied at midrapidity in pp and central Pb–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision sNN=5.02 TeV with the ALICE detector at the LHC. After subtracting the contributions of the flow background, the per-trigger yields are extracted on both the near and away sides, and the ratio in Pb–Pb collisions with respect to pp collisions (IAA) is computed. The per-trigger yield in Pb–Pb collisions on the away side is strongly suppressed to the level of IAA≈ 0.6 for pT , assoc> 3 GeV/ c as expected from strong in-medium energy loss, while an enhancement develops at low pT , assoc on both the near and away sides, reaching IAA≈ 1.8 and 2.7 respectively. These findings are in good agreement with previous ALICE measurements from two-particle correlations triggered by neutral pions (π –h) and charged hadrons (h–h) in Pb–Pb collisions at sNN=2.76 TeV. Moreover, the correlations with KS0 mesons and Λ / Λ ¯ baryons as trigger particles are compared to those of inclusive charged hadrons. The results are compared with the predictions of Monte Carlo models.