At su ciently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP) 1 . Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed 2-6 . Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions 7 , is more pronounced for multi-strange baryons. Several e ects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions 8,9 , but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results 10,11 , indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.The production of strange hadrons in high-energy hadronic interactions provides a way to investigate the properties of quantum chromodynamics (QCD), the theory of strongly interacting matter. Unlike up (u) and down (d) quarks, which form ordinary matter, strange (s) quarks are not present as valence quarks in the initial state, yet they are sufficiently light to be abundantly created during the course of the collisions. In the early stages of high-energy collisions, strangeness is produced in hard (perturbative) 2 → 2 partonic scattering processes by flavour creation (gg → ss, qq → ss) and flavour excitation (gs → gs, qs → qs). Strangeness is also created

Comprehensive results on the production of unidentified charged particles, π

Invariant differential yields of deuterons and antideuterons in pp collisions at √ s = 0.9, 2.76 and 7 TeV and the yields of tritons, 3 He nuclei, and their antinuclei at √ s = 7 TeV have been measured with the ALICE detector at the CERN Large Hadron Collider. The measurements cover a wide transverse momentum (p T ) range in the rapidity interval |y| < 0.5, extending both the energy and the p T reach of previous measurements up to 3 GeV/c for A = 2 and 6 GeV/c for A = 3. The coalescence parameters of (anti)deuterons and 3 He nuclei exhibit an increasing trend with p T and are found to be compatible with measurements in pA collisions at low p T and lower energies. The integrated yields decrease by a factor of about 1000 for each increase of the mass number with one (anti)nucleon. Furthermore, the deuteron-to-proton ratio is reported as a function of the average charged particle multiplicity at different center-of-mass energies.

We report the measurements of correlations between event-by-event fluctuations of amplitudes of anisotropic flow harmonics in nucleus-nucleus collisions, obtained for the first time using a new analysis method based on multiparticle cumulants in mixed harmonics. This novel method is robust against systematic biases originating from nonflow effects and by construction any dependence on symmetry planes is eliminated. We demonstrate that correlations of flow harmonics exhibit a better sensitivity to medium properties than the individual flow harmonics. Comparisons are made to predictions from Monte Carlo Glauber, viscous hydrodynamics, AMPT, and HIJING models. Together with the existing measurements of the individual flow harmonics the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.

We report measurements of the production of prompt D 0 , D + , D * + and D + s mesons in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair √ s NN = 5.02 TeV, in the centrality classes 0-10%, 30-50% and 60-80%. The D-meson production yields are measured at mid-rapidity (|y| < 0.5) as a function of transverse momentum (p T). The p T intervals covered in central collisions are: 1 < p T < 50 GeV/c for D 0 , 2 < p T < 50 GeV/c for D + , 3 < p T < 50 GeV/c for D * + , and 4 < p T < 16 GeV/c for D + s mesons. The nuclear modification factors (R AA) for non-strange D mesons (D 0 , D + , D * +) show minimum values of about 0.2 for p T = 6-10 GeV/c in the most central collisions and are compatible within uncertainties with those measured at √ s NN = 2.76 TeV. For D + s mesons, the values of R AA are larger than those of non-strange D mesons, but compatible within uncertainties. In central collisions the average R AA of non-strange D mesons is compatible with that of charged particles for p T > 8 GeV/c, while it is larger at lower p T. The nuclear modification factors for strange and non-strange D mesons are also compared to theoretical models with different implementations of in-medium energy loss.