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Item type:Publication, Measurement of anti-3He nuclei absorption in matter and impact on their propagation in the Galaxy(Nature Portfolio, 2022-12-12)In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ momentum from 25% to 90% for cosmic-ray sources. The results indicate that $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, ALICE luminosity determination for Pb-Pb collisions at √sNN = 5.02 TeV(Institute of Physics, 2024-02-01)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 √s NN= 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 √s NN= 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.4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of inclusive charged-particle jet production in pp and p–Pb collisions(Springer Science and Business Media Deutschland GmbH, 2024-05-01)Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision sNN = 5.02 TeV and the corresponding nuclear modification factor RpPbchjet are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |ηjet| < 0.5 from charged particles using the anti-kT algorithm with resolution parameters R = 0.2, 0.3, and 0.4. The pT-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10 <pT,jetch< 140 GeV/c and 10 <pT,jetch< 160 GeV/c, respectively, together with the nuclear modification factor RpPbchjet in the range 10 <pT,jetch< 140 GeV/c. The analysis extends the pT range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at sNN = 5.02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD Powheg calculations with parton shower provided by Pythia8 as well as by Jetscape simulations. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, ALICE upgrades during the LHC Long Shutdown 2(Institute of Physics, 2024-05-01)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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, First measurement of the |t| dependence of incoherent J/ψ photonuclear production(American Physical Society, 2024-04-19)The first measurement of the cross section for incoherent photonuclear production of J/ψ vector mesons as a function of the Mandelstam |t| variable is presented. The measurement was carried out with the ALICE detector at midrapidity, |y|<0.8, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of sNN=5.02 TeV. This rapidity interval corresponds to a Bjorken-x range (0.3-1.4)×10-3. Cross sections are given in five |t| intervals in the range 0.04<|t|<1 GeV2 and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a |t| dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, ψ(2S) suppression in Pb–Pb collisions at the LHC(American Physical Society, 2024-01-26)The production of the ψ(2S) charmonium state was measured with ALICE in Pb-Pb collisions at sNN=5.02 TeV, 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 the ψ(2S) and J/ψ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region pT<12 GeV/c. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio [σψ(2S)/σJ/ψ]Pb-Pb/[σψ(2S)/σJ/ψ]pp. It is found that in Pb-Pb collisions the ψ(2S) is suppressed by a factor of ∼2 with respect to the J/ψ. The ψ(2S) nuclear modification factor RAA was also obtained as a function of both centrality and pT. The results show that the ψ(2S) resonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up to ∼3 with respect to pp. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and of RAA with higher-pT results 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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Measurement of the fraction of jet longitudinal momentum carried by Λc+ baryons in pp collisions(American Physical Society, 2024-04-01)Recent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried by Λc+ baryons, z∥ch, in hadronic collisions. The results are obtained in proton-proton (pp) collisions at s=13 TeV at the LHC, with Λc+ baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of 3≤pTΛc+<15 GeV/c and 7≤pTjet ch<15 GeV/c, respectively. The z∥ch distribution is compared to a measurement of D0-tagged charged jets in pp collisions as well as to pythia 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronization models which include color correlations beyond leading-color in the string formation. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Σ(1385)± Resonance Production in Pb–Pb Collisions at √sNN = 5.02 TeV(Institute for Ionics, 2023-05-01)Hadronic resonances are used to probe the hadron gas produced in the late stage of heavy-ion collisions since they decay on the same timescale, of the order of 1–10 fm/c, as the decoupling time of the system. In the hadron gas, (pseudo)elastic scatterings among the products of resonances that decayed before the kinetic freeze-out and regeneration processes counteract each other, the net effect depending on the resonance lifetime, the duration of the hadronic phase, and the hadronic cross sections at play. In this context, the Σ (1385) ± particle is of particular interest as models predict that regeneration dominates over rescattering despite its relatively short lifetime of about 5.5 fm/c. The first measurement of the Σ (1385) ± resonance production at midrapidity in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, Λ π , as a function of the transverse momentum (pT) and the collision centrality. The results are discussed in comparison with the measured yield of pions and with expectations from the statistical hadronization model as well as commonly employed event generators, including PYTHIA8/Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For Σ (1385) ± , a similar behaviour as K ∗(892) is observed in data unlike the predictions of EPOS3 with afterburner.8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, W±-Boson Production in p–Pb Collisions at √sNN = 8.16 TeV and Pb–Pb Collisions at √sNN = 5.02 TeV(Springer Science and Business Media Deutschland GmbH, 2023-05-01)The production of the W± bosons measured in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision sNN = 8.16 TeV and Pb–Pb collisions at sNN = 5.02 TeV with ALICE at the LHC is presented. The W± bosons are measured via their muonic decay channel, with the muon reconstructed in the pseudorapidity region −4 < ηlabμ < −2.5 with transverse momentum pTμ > 10 GeV/c. While in Pb–Pb collisions the measurements are performed in the forward (2.5 < ycmsμ < 4) rapidity region, in p–Pb collisions, where the centre-of-mass frame is boosted with respect to the laboratory frame, the measurements are performed in the backward (−4.46 < ycmsμ < −2.96) and forward (2.03 < ycmsμ < 3.53) rapidity regions. The W− and W+ production cross sections, lepton-charge asymmetry, and nuclear modification factors are evaluated as a function of the muon rapidity. In order to study the production as a function of the p–Pb collision centrality, the production cross sections of the W− and W+ bosons are combined and normalised to the average number of binary nucleon–nucleon collision 〈N coll〉. In Pb–Pb collisions, the same measurements are presented as a function of the collision centrality. Study of the binary scaling of the W±-boson cross sections in p–Pb and Pb–Pb collisions is also reported. The results are compared with perturbative QCD calculations, with and without nuclear modifications of the Parton Distribution Functions (PDFs), as well as with available data at the LHC. Significant deviations from the theory expectations are found in the two collision systems, indicating that the measurements can provide additional constraints for the determination of nuclear PDFs and in particular of the light-quark distributions. [Figure not available: see fulltext.]. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Underlying-Event Properties in pp and p–Pb Collisions at √sNN = 5.02 TeV(Springer Science and Business Media Deutschland GmbH, 2023-06-01)We report about the properties of the underlying event measured with ALICE at the LHC in pp and p–Pb collisions at sNN = 5.02 TeV. The event activity, quantified by charged-particle number and summed-p T densities, is measured as a function of the leading-particle transverse momentum (pTtrig) . These quantities are studied in three azimuthal-angle regions relative to the leading particle in the event: toward, away, and transverse. Results are presented for three different p T thresholds (0.15, 0.5 and 1 GeV/c) at mid-pseudorapidity (|η| < 0.8). The event activity in the transverse region, which is the most sensitive to the underlying event, exhibits similar behaviour in both pp and p–Pb collisions, namely, a steep increase with pTtrig for low pTtrig , followed by a saturation at pTtrig≈5 GeV/c. The results from pp collisions are compared with existing measurements at other centre-of-mass energies. The quantities in the toward and away regions are also analyzed after the subtraction of the contribution measured in the transverse region. The remaining jet-like particle densities are consistent in pp and p–Pb collisions for pTtrig>10 GeV/c, whereas for lower pTtrig values the event activity is slightly higher in p–Pb than in pp collisions. The measurements are compared with predictions from the PYTHIA 8 and EPOS LHC Monte Carlo event generators. [Figure not available: see fulltext.].