1,176 research outputs found

    What Shall we do with the Spectator System in Ultrarelativistic Heavy-ion Collisions?

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    International audienceThis paper briefly reviews the first results of a coordinated study aimed at the clarification of the interplay between spectator fragmentation and electromagnetic phenomena in ultrarelativistic heavy-ion collisions at CERN SPS energies. The available experimental and phenomenological results are put in the context of recent theoretical calculations

    Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV

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    We present the first ever measurements of femtoscopic correlations between the K-S(0) and K-+/- particles. The analysis was performed on the data from Pb-Pb collisions at root S-NN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a(0) resonance are tested. Our results are also compatible with the interpretation of the a(0) having a tetraquark structure instead of that of a diquark. (c) 2017 The Author. Published by Elsevier B.V

    Measurement of the production of high-p(T) electrons from heavy-flavour hadron decays in Pb-Pb collisions at root s(NN)=2.76 TeV

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    Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy root s(NN) = 2.76 TeV. The transverse momentum (pT) differential production yields at mid-rapidity were used to calculate the nuclear modification factor R-AA in the interval 3 < p(T) < 18 GeV/c. The R-AA shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad p(T) interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC. (C) 2017 The Author. Published by Elsevier B.V

    First study of the two-body scattering involving charm hadrons

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    This article presents the first measurement of the interaction between charm hadrons and nucleons. The two-particle momentum correlations of pD− and ̄pD+ pairs are measured by the ALICE Collaboration in high-multiplicity pp collisions at sqrt(s) = 13 TeV. The data are compatible with the Coulomb-only interaction hypothesis within 1.1–1.5 σ. The level of agreement slightly improves if an attractive nucleon (N) ̄D strong interaction is considered, in contrast to most model predictions which suggest an overall repulsive interaction. This measurement allows for the first time an estimation of the 68% confidence level interval for the isospin I = 0 inverse scattering length of the N ̄D state f−1 0;I=0 ∈ [−0.4; 0.9] fm−1, assuming negligible interaction for the isospin I = 1 channel

    Search for Quasiparticle Scattering in the Quark-Gluon Plasma with Jet Splittings in <i>pp</i> and Pb-Pb Collisions at √<i>S</i><sub>NN</sub>=5.02 TeV

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    The ALICE Collaboration reports measurements of the large relative transverse momentum (k(T)) component of jet substructure in pp and Pb-Pb collisions at center-of-mass energy per nucleon pair root S-NN = 5.02 TeV. Enhancement in the yield of such large-k(T) emissions in head-on Pb-Pb collisions is predicted to arise from partonic scattering with quasiparticles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti-kT algorithm with resolution parameter R = 0.2 in the transverse-momentum interval 60 < p(T,ch,jet) < 80 GeV/c. The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb-Pb and pp collisions shows medium-induced narrowing, corresponding to yield suppression of high-k(T) splittings, in contrast to the expectation of yield enhancement due to quasiparticle scattering. The measurements are compared to theoretical model calculations incorporating jet modification due to jet-medium interactions ("jet quenching"), both with and without quasiparticle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching

    First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production

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    The first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V
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