Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud - IV. Evidence for multiple populations in Hodge 11 and NGC 2210

We present a multiple population search in two old Large Magellanic Cloud (LMC) Globular clusters, Hodge 11 and NGC 2210. This work uses data from the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope from programme GO- 14164 in Cycle 23. Both of these clusters exhibit a broadened main sequence with the second population representing (20±~5) per cent forNGC2210 and (30±~5) per cent forHodge 11. In both clusters, the smaller population is redder than the primary population, suggesting CNO variations. Hodge 11 also displays a bluer second population in the horizontal branch, which is evidence for helium enhancement. However, even though NGC 2210 shows similarities to Hodge 11 in the main sequence, there does not appear to be a second population on NGC 2210's horizontal branch. This is the first photometric evidence that ancient LMC Globular clusters exhibit multiple stellar populations.Fil: Gilligan, Christina K.. Dartmouth College; Estados UnidosFil: Chaboyer, Brian. Dartmouth College; Estados UnidosFil: Cummings, Jeffrey D.. University Johns Hopkins; Estados UnidosFil: Mackey, Dougal. Australian National University. Research School of Astronomy & Astrophysics; AustraliaFil: Cohen, Roger E.. Space Telescope Science Institute; Estados UnidosFil: Geisler, Douglas. Universidad de La Serena; ChileFil: Grocholski, Aaron J.. University of Washington; Estados UnidosFil: Parisi, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Ventura, Paolo. Osservatorio Astronomico Di Roma; ItaliaFil: Villanova, Sandro. Universidad de Concepción; ChileFil: Yang, Soung-Chul. Korea Astronomy And Space Science Institute; Corea del SurFil: Wagner-Kaiser, Rachel. University of Florida; Estados Unido

Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud - V. Multiple populations in ancient globular clusters

We examine four ancient LargeMagellanic Cloud (LMC) globular clusters (GCs) for evidence of multiple stellar populations using the Advanced Camera for Surveys andWide Field Camera 3 on the Hubble Space Telescope Programme GO-14164. NGC 1466, NGC 1841, and NGC 2257 all show evidence for a redder, secondary population along themain sequence. Reticulum does not showevidence for the presence of a redder population, but thisGChas the least number of stars and Monte Carlo simulations indicate that the sample of main-sequence stars is too small to robustly infer whether a redder population exists in this cluster. The second, redder, population of the other three clusters constitutes ∼ 30 - 40 per cent of the total population along the main sequence. This brings the total number of ancient LMC GCs with known split or broadened main sequences to five. However, unlike for Hodge 11 and NGC 2210 (see Gilligan et al. (2019)), none of the clusters shows evidence for multiple populations in the horizontal branch. We also do not find evidence of a second population along the red giant branch.Fil: Gilligan, Christina K.. Dartmouth College; Estados UnidosFil: Chaboyer, Brian. Dartmouth College; Estados UnidosFil: Cummings, Jeffrey D.. University Johns Hopkins; Estados UnidosFil: Mackey, Dougal. Australian National University; AustraliaFil: Cohen, Roger E.. Space Telescope Science Institute; Estados UnidosFil: Geisler, Douglas. Universidad de Concepción; ChileFil: Grocholski, Aaron J.. University of Florida; Estados UnidosFil: Parisi, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sarajedini, Ata. University of Florida; Estados UnidosFil: Ventura, Paolo. Osservatorio Astronomico Di Roma; ItaliaFil: Villanova, Sandro. Universidad de Concepción; ChileFil: Yang, Soung-Chul. Korea Astronomy And Space Science Institute; Corea del SurFil: Wagner-Kaiser, Rachel. University of Florida; Estados Unido

Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV

Midrapidity production of π±, K±, and (¯p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0–90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √sNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT≈3 GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √sNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at √sNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.publishedVersio

Study of J/ψ azimuthal anisotropy at forward rapidity in Pb-Pb collisions at √sNN=5.02 TeV

The second (v2) and third (v3) flow harmonic coefficients of J/ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at √ sNN = 5.02 TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, pT, for various collision centralities. A positive value of J/ψ v3 is observed with 3.7σ significance. The measurements, compared to those of prompt D0 mesons and charged particles at mid-rapidity, indicate an ordering with vn(J/ψ) < vn(D0 ) < vn(h±) (n = 2, 3) at low and intermediate pT up to 6 GeV/c and a convergence with v2(J/ψ) ≈ v2(D0 ) ≈ v2(h±) at high pT above 6–8 GeV/c. In semicentral collisions (5–40% and 10–50% centrality intervals) at intermediate pT between 2 and 6 GeV/c, the ratio v3/v2 of J/ψ mesons is found to be significantly lower (4.6σ) with respect to that of charged particles. In addition, the comparison to the prompt D0 -meson ratio in the same pT interval suggests an ordering similar to that of the v2 and v3 coefficients. The J/ψ v2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry.publishedVersio

Measurement of isolated photon-hadron correlations in √sNN = 5.02 TeV pp and p-Pb collisions

This paper presents isolated photon-hadron correlations using pp and p-Pb data collected by the ALICE detector at the LHC. For photons with |η|<0.67 and 12<pT<40 GeV/c, the associated yield of charged particles in the range |η|<0.80 and 0.5<pT<10 GeV/c is presented. These momenta are much lower than previous measurements at the LHC. No significant difference between pp and p-Pb is observed, with Pythia 8.2 describing both data sets within uncertainties. This measurement constrains nuclear effects on the parton fragmentation in p-Pb collisions, and provides a benchmark for future studies of Pb-Pb collisions.publishedVersio

Constraining the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 and 5.02 TeV

Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity (η) and transverse momentum (pT) ranges |η| < 0.8 and 0.2 < pT < 5 GeV/c. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators γ1, 1 = 〈cos(φα + φβ − 2Ψ2)〉 and γ1, − 3 = 〈cos(φα − 3φβ + 2Ψ2)〉. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured γ1,1. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form γ1, 2 = 〈cos(φα + 2φβ − 3Ψ3)〉, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of γ1,1.publishedVersio

Spin alignment measurements using vector mesons with ALICE detector at the LHC

We present new measurements related to spin alignment of K*0 vector mesons at mid-rapidity for Pb–Pb collisions at √sNN = 2.76 and 5.02 TeV. The spin alignment measurements are carried out with respect to production plane and 2nd order event plane. At low pT the spin density matrix element ρ00 for K*0 is found to have values slightly below 1/3, while it is consistent with 1/3, i.e. no spin alignment, at high pT. Similar values of ρ00 are observed with respect to both production plane and event plane. Within statistical and systematic uncertainties, ρ00 values are also found to be independent of √sNN. ρ00 also shows centrality dependence with maximum deviation from 1/3 for mid-central collisions with respect to both the kinematic planes. The measurements for K*0 in pp collisions at √s = 13 TeV and for K0S (a spin 0 hadron) in 20-40% central Pb–Pb collisions at √sNN = 2.76 TeV are consistent with no spin alignment.publishedVersio

J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at √sNN = 8.16 TeV

Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sNN−−−√ = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.publishedVersio

J/ψ elliptic and triangular flow in Pb-Pb collisions at √sNN = 5.02 TeV

The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at sNN−−−√ = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 < pT < 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow.publishedVersio

Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at √sNN=5.02 TeV

The measurements of the (anti)deuteron elliptic flow (v2) and the first measurements of triangular flow (v3) in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision √sNN = 5.02 TeV are presented. A mass ordering at low transverse momentum (pT) is observed when comparing these measurements with those of other identified hadrons, as expected from relativistic hydrodynamics. The measured (anti)deuteron v2 lies between the predictions from the simple coalescence and blast-wave models, which provide a good description of the data only for more peripheral and for more central collisions, respectively. The mass number scaling, which is violated for v2, is approximately valid for the (anti)deuterons v3. The measured v2 and v3 are also compared with the predictions from a coalescence approach with phase-space distributions of nucleons generated by iebe-vishnu with ampt initial conditions coupled with urqmd, and from a dynamical model based on relativistic hydrodynamics coupled to the hadronic afterburner smash. The model predictions are consistent with the data within the uncertainties in midcentral collisions, while a deviation is observed in the most central collisions.publishedVersio