Coherent photoproduction of rho(0) vector mesons in ultra-peripheral Pb-Pb collisions at root s(NN)=5.02 TeV

Cross sections for the coherent photoproduction of rho(0) vector mesons in ultra-peripheral Pb-Pb collisions at root s(NN) = 5.02 TeV are reported. The measurements, which rely on the pi(+)pi(-) decay channel, are presented in three regions of rapidity covering the range vertical bar y vertical bar <0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c(2) and a width of about 140 MeV/c(2) is reported and compared with similar observations from other experiments.Peer reviewe

Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at root s(NN)=5.02 TeV

Anisotropic flow coefficients, nu(n), non-linear flow mode coefficients, chi(n,mk), and correlations among different symmetry planes, rho(n,mk) are measured in Pb-Pb collisions at root s(NN) = 5.02TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 <p(T) <5.0 GeV/c within the pseudorapidity interval 0.4 <vertical bar eta vertical bar <0.8 as a function of collision centrality. The nu(n) coefficients and chi(n,mk) and rho(n,mk) are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system.Peer reviewe

Investigation of the p-Sigma(0) interaction via femtoscopy in pp collisions

This Letter presents the first direct investigation of the p-Sigma(0) interaction, using the femtoscopy technique in high-multiplicity pp collisions at root s = 13 TeV measured by the ALICE detector. The Sigma(0) is reconstructed via the decay channel to Lambda gamma, and the subsequent decay of Lambda to p pi(-). The photon is detected via the conversion in material to e(+)e(-) pairs exploiting the capability of the ALICE detector to measure electrons at low transverse momenta. The measured p-Sigma(0) correlation indicates a shallow strong interaction. The comparison of the data to several theoretical predictions obtained employing the Correlation Analysis Tool using the Schrodinger Equation (CATS) and the Lednicky-Lyuboshits approach shows that the current experimental precision does not yet allow to discriminate between different models, as it is the case for the available scattering and hypernuclei data. Nevertheless, the p-Sigma(0) correlation function is found to be sensitive to the strong interaction, and driven by the interplay of the different spin and isospin channels. This pioneering study demonstrates the feasibility of a femtoscopic measurement in the p-Sigma(0) channel and with the expected larger data samples in LHC Run 3 and Run 4, the p-Sigma(0) interaction will be constrained with high precision. (C) 2020 European Organization for Nuclear Research. Published by Elsevier B.V.Peer reviewe

Global baryon number conservation encoded in net-proton fluctuations measured in Pb-Pb collisions at root s(NN)=2.76TeV

Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb-Pb collisions at root s(NN)= 2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event- by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions. (C) 2020 European Organization for Nuclear Research. Published by Elsevier B.V.Peer reviewe

Centrality and transverse momentum dependence of inclusive J/psi production at midrapidity in Pb-Pb collisions at root s NN=5 .02 TeV

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Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at root s(NN)=2.76 TeV

This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators G(2)(CI) and G(2)(CD) in Pb-Pb collisions at root sNN= 2.76 TeVby the ALICE collaboration. The two-particle transverse momentum correlator G(2) was introduced as a measure of the momentum current transfer between neighboringsystem cells. The correlators are measured as a function of pair separation in pseudorapidity (Delta eta) and azimuth (Delta phi) and as a function of collision centrality. From peripheral to central collisions, the correlator G(2)(CI) exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, G(2)(CD) exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density./sof the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of eta/s and is in qualitative agreement with values obtained from anisotropic flow measurements. (c) 2020 Conseil Europeen pour la Recherche Nucleaire,. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe