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  1. Accuracy of environmental tracers and consequences for determining the Type Ia supernova magnitude step

    Type Ia Supernovae (SNe Ia) are standardizable candles that allow us to measure the recent expansion rate of the Universe. Due to uncertainties in progenitor physics, potential astrophysical dependencies may bias cosmological measurements if not properly accounted for. The dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is often used to standardize SNe Ia luminosity and is commonly parameterized as a step function. This functional form implicitly assumes two-populations of SNe Ia. In the literature, multiple environmental indicators have been considered, finding different, sometimes incompatible, step function amplitudes. We compare these indicators in the context ofmore » a two-populations model, based on their ability to distinguish the two populations. We show that local Hα-based specific star formation rate (lsSFR) and global stellar mass are better tracers than, for instance, host galaxy morphology. We show that tracer accuracy can explain the discrepancy between the observed SNe Ia step amplitudes found in the literature. Using lsSFR or global mass to identify the two populations can explain all other observations, though lsSFR is favoured. As lsSFR is strongly connected to age, our results favour a prompt and delayed population model. In any case, there exists two populations that differ in standardized magnitude by at least 0.121 ± 0.010 mag.« less
  2. First measurement of quarkonium polarization in nuclear collisions at the LHC

    The polarization of inclusive J/ψ and Υ(1S) produced in Pb–Pb collisions atmore » $$\sqrt{s_{NN}}$$=5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5« less
  3. Measurement of jet-medium interactions via direct photon-hadron correlations in Au + Au and d + Au collisions at s N N = 200 GeV

    We present direct photon-hadron correlations in 200 GeV/A Au+Au, d+Au and p+p collisions, for direct photon pT from 5--12 GeV/c, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in d+Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au+Au compared to p+p and d+Au. As the momentum fraction decreases, the yield of hadrons in Au+Au increases to an excess over the yield in p+p collisions. The excess is at large angles and atmore » low hadron pT and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.« less
  4. K * ( 892 ) 0 and ϕ ( 1020 ) production at midrapidity in p p collisions at s = 8 TeV

    The production of K*(892)0 and Φ(1020) in pp collisions at √s = 8 TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The pT-differential yields d2N/dydpT in the range 0 < pT < 20 GeV/c for K*0 and 0.4 < pT < 16 GeV/c for Φ have been measured at midrapidity, |y| < 0.5. Moreover, improved measurements of the K*0 (892) and Φ(1020) at √s = 7 TeV are presented. The collision energy dependence of pT distributions, pT-integrated yields, and particle ratios in inelastic pp collisions are examined. Themore » results are also compared with different collision systems. Here, the values of the particle ratios are found to be similar to those measured at other LHC energies. In pp collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The pT-differential yields of K*0 and Φ in pp collisions at √s = 8 TeV are compared with the expectations of different Monte Carlo event generators.« less
  5. Measurement of the (anti-)3He elliptic flow in Pb–Pb collisions at s NN = 5.02 TeV

    Tmore » he elliptic flow ( v 2 ) of (anti-)3He is measured in Pb–Pb collisions at s NN = 5.02 eV in the transverse-momentum ( p ) range of 2–6 GeV/c for the centrality classes 0–20%, 20–40%, and 40–60% using the event-plane method. his measurement is compared to that of pions, kaons, and protons at the same center-of-mass energy. A clear mass ordering is observed at low p , as expected from relativistic hydrodynamics. he violation of the scaling of v 2 with the number of constituent quarks at low p , already observed for identified hadrons and deuterons at LHC energies, is confirmed also for (anti-)3He. he elliptic flow of (anti-)3He is underestimated by the Blast-Wave model and overestimated by a simple coalescence approach based on nucleon scaling. he elliptic flow of (anti-)3He measured in the centrality classes 0–20% and 20–40% is well described by a more sophisticated coalescence model where the phase-space distributions of protons and neutrons are generated using the iEBE-VISHNU hybrid model with AMP initial conditions.« less
  6. Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at s NN = 5.02 TeV

    The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions atmore » $$\sqrt{s_{NN}}$$ in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at $$\sqrt{s}$$ = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC.« less
  7. 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 (more » $$^¯_p)p$$ measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic p p collisions at $$\sqrt{sNN}=5.02$$ 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 $$\sqrt{sNN}=2.76$$ 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 p p collisions at the same energy and in Pb-Pb collisions at $$\sqrt{sNN}=2.76$$ 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 $$\sqrt{sNN}=2.76$$ TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.« less
  8. Global polarization of ΛΛ¯ hyperons in Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV

    Tmore » he global polarization of the Λ and Λ ¯ hyperons is measured for Pb-Pb collisions at s N N = 2.76 and 5.02 eV recorded with the ALICE at the Large Hadron Collider (LHC). he results are reported differentially as a function of collision centrality and hyperon's transverse momentum ( p ) for the range of centrality 5–50%, 0.5 < p < 5 GeV/ c , and rapidity | y | < 0.5 . he hyperon global polarization averaged for Pb-Pb collisions at s N N = 2.76 and 5.02 eV is found to be consistent with zero, ( P H ) ( % ) 0.01 ± 0.06 (stat.) ± 0.03 (syst.) in the collision centrality range 15–50%, where the largest signal is expected. he results are compatible with expectations based on an extrapolation from measurements at lower collision energies at the Relativistic Heavy Ion Collider, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of 0.01 % .« less
  9. Scattering Studies with Low-Energy Kaon-Proton Femtoscopy in Proton-Proton Collisions at the LHC

    Tmore » he study of the strength and behavior of the antikaon-nucleon ( K ¯ N ) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. he femtoscopic measurements of the correlation function at low pair-frame relative momentum of ( K + p K - p ¯ ) and ( K - p K + p ¯ ) pairs measured in p p collisions at s = 5 , 7, and 13 eV are reported. A structure observed around a relative momentum of 58 MeV / c in the measured correlation function of ( K - p K + p ¯ ) with a significance of 4.4 σ constitutes the first experimental evidence for the opening of the ( K ¯ 0 n K 0 n ¯ ) isospin breaking channel due to the mass difference between charged and neutral kaons. he measured correlation functions have been compared to Jülich and Kyoto models in addition to the Coulomb potential. he high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the K ¯ N threshold for low-energy QCD chiral models.« less
  10. Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies

    The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at √s = 7 TeV and central Pb–Pb collisions at √sNN=2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the zg, and its dependence on the opening angle, in both pp and Pb–Pb collisions. We also present the measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hardmore » splittings. In Pb–Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as colour coherence.« less

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