Search results for "Pb-Pb collisions"
showing 10 items of 39 documents
Azimuthally Differential Pion Femtoscopy in Pb-Pb Collisions at √sNN = 2.76 TeV
2017
We present the first azimuthally differential measurements of the pion source size relative to the second harmonic event plane in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of √ s N N = 2.76 TeV . The measurements have been performed in the centrality range 0%–50% and for pion pair transverse momenta 0.2 < k T < 0.7 GeV / c . We find that the R side and R out radii, which characterize the pion source size in the directions perpendicular and parallel to the pion transverse momentum, oscillate out of phase, similar to what was observed at the Relativistic Heavy Ion Collider. The final-state source eccentricity, estimated via R side oscillations, is found to b…
Λc+ production in Pb–Pb collisions at √sNN = 5.02 TeV
2019
A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λc+ → pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT <12 GeV/c and 0–80%. The Λc+/D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at √s = 7 TeV and in p–Pb collisions at √sNN = 5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined s…
Centrality dependence of pion freeze-out radii in Pb-Pb collisions at √sNN = 2.76 TeV
2016
We report on the measurement of freeze-out radii for pairs of identical-charge pions measured in Pb-Pb collisions at √sNN = 2.76 TeV as a function of collision centrality and the average transverse momentum of the pair kT. Three-dimensional sizes of the system (femtoscopic radii), as well as direction-averaged onedimensional radii are extracted. The radii decrease with kT, following a power-law behavior. This is qualitatively consistent with expectations from a collectively expanding system, produced in hydrodynamic calculations. The radii also scale linearly with dNch/dη 1/3. This behavior is compared to world data on femtoscopic radii in heavy-ion collisions. While the dependence is quali…
Charge-dependent flow and the search for the chiral magnetic wave in Pb-Pb collisions at √sNN = 2.76 TeV
2016
We report on measurements of a charge-dependent flow using a novel three-particle correlator with ALICE in Pb-Pb collisions at the CERN Large Hadron Collider (LHC), and discuss the implications for observation of local parity violation and the chiral magnetic wave (CMW) in heavy-ion collisions. Charge-dependent flow is reported for different collision centralities as a function of the event charge asymmetry. While our results are in qualitative agreement with expectations based on the CMW, the nonzero signal observed in higher harmonics correlations indicates a possible significant background contribution. We also present results on a differential correlator, where the flow of positive and …
Anisotropic Flow of Charged Particles in Pb-Pb Collisions at √sNN = 5.02 TeV
2016
We report the first results of elliptic (v2), triangular (v3), and quadrangular (v4) flow of charged particles in Pb-Pb collisions at a center-of-mass energy per nucleon pair of √sNN p ¼ 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurements are performed in the central pseudorapidity region jηj < 0.8 and for the transverse momentum range 0.2 < pT < 5 GeV=c. The anisotropic flow is measured using two-particle correlations with a pseudorapidity gap greater than one unit and with the multiparticle cumulant method. Compared to results from Pb-Pb collisions at √sNN p ¼ 2.76 TeV, the anisotropic flow coefficients v2, v3, and v4 are found to increase by ð3.0 0.6Þ%, ð…
Flow dominance and factorization of transverse momentum correlations in Pb-Pb collisions at the LHC
2017
Physical review letters 118(16), 162302 (2017). doi:10.1103/PhysRevLett.118.162302
Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at √sNN = 2.76 TeV
2016
Transverse momentum (pT) spectra of pions, kaons, and protons up to pT = 20 GeV/c have been measured in Pb-Pb collisions at √sNN = 2.76 TeV using the ALICE detector for six different centrality classes covering 0%–80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb-Pb collisions that decreases for more peripheral collisions. For pT > 10 GeV/c, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10%–20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of …
First measurement of the |t|-dependence of coherent J/ψ photonuclear production
2021
The first measurement of the dependence on $|t|$, the square of the momentum transferred between the incoming and outgoing target nucleus, of coherent J/ψ photoproduction is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the J/$\psi$ produced in the central rapidity region $|y| < 0.8$, which corresponds to the small Bjorken-$x$ range $(0.3 − 1.4) \times 10 ^{−3}$. The measured $|t|$-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 t…
Event-by-event fluctuations in a perturbative QCD plus saturation plus hydrodynamics model : Determining QCD matter shear viscosity in ultrarelativis…
2016
We introduce an event-by-event perturbative-QCD + saturation + hydro ("EKRT") framework for ultrarelativistic heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading-order perturbative QCD using a saturation conjecture to control soft-particle production and describe the space-time evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuth-angle asymmetries against the LHC and RHIC measurements. We compare also the computed event-by-event probability distribut…
Measurement of transverse energy at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV
2016
We report the transverse energy (ET) measured with ALICE at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single-particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean ET per unit pseudorapidity (η), dET/dη , in 0%–5% central collisions is 1737 ± 6(stat.) ± 97(sys.) GeV. We find a similar centrality dependence of the shape of dET/dη as a function of the number of participating …