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  1. Abstract

    A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.

     
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    Free, publicly-accessible full text available May 1, 2025
  2. Abstract

    Luminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb–Pb collisions at a centre-of-mass energy per nucleon pair of √sNN= 5.02 TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan.This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb–Pb collisions at √sNN= 5.02 TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be 7.67 ± 0.25 b, in agreement with predictions using the Glauber model.

     
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    Free, publicly-accessible full text available February 1, 2025
  3. The production of theψ(2S)charmonium state was measured with ALICE in Pb-Pb collisions atsNN=5.02TeV, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity (2.5<y<4). The measurement of the ratio of the inclusive production cross sections of theψ(2S)andJ/ψresonances is reported as a function of the centrality of the collisions and of transverse momentum, in the regionpT<12GeV/c. The results are compared with the corresponding measurements inppcollisions, by forming the double ratio[σψ(2S)/σJ/ψ]PbPb/[σψ(2S)/σJ/ψ]pp. It is found that in Pb-Pb collisions theψ(2S)is suppressed by a factor of2with respect to theJ/ψ. Theψ(2S)nuclear modification factorRAAwas also obtained as a function of both centrality andpT. The results show that theψ(2S)resonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up to3with respect topp. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and ofRAAwith higher-pTresults at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the presence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.

    © 2024 CERN, for the ALICE Collaboration2024CERN 
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    Free, publicly-accessible full text available January 1, 2025