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 √s NN =2.76 TeV. The transverse momentum (p T ) ...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.
The second and the third order anisotropic flow, V2 and V3, are mostly determined by the corresponding initial spatial anisotropy coefficients, ε2 and ε3, in the initial density distribution. In ...addition to their dependence on the same order initial anisotropy coefficient, higher order anisotropic flow, Vn(n >3), can also have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this Letter we investigate the linear and non-linear modes in higher order anisotropic flow Vn for n =4, 5, 6 with the ALICE detector at the Large Hadron Collider. The measurements are done for particles in the pseudorapidity range |η| <0.8 and the transverse momentum range 0.2 <pT<5.0GeV/c as a function of collision centrality. The results are compared with theoretical calculations and provide important constraints on the initial conditions, including initial spatial geometry and its fluctuations, as well as the ratio of the shear viscosity to entropy density of the produced system.
The work conditions of the hadron calorimeter for spectators registration (Zero Degree Calorimeter, ZDC) were studied for the heavy nuclei collisions with the several GeV invariant energy. The ZDC ...simulations were performed for the MPD (Multi-Purpose Detector) at the NICA (Nuclotron-based Ion Collider fAcility) collider, which are under developement at the Joint Institute for Nuclear Research (JINR, Dubna). Taking into account the spectator nuclear fragments leads to a nonmonotonic dependence of the ZDC response on the impact parameter. The reason for this dependence studied with several event generators is the primary beam hole in the ZDC center. It is shown, that the ZDC signal should be combined with a data from other MPD@NICA detector subsystems to determine centrality.
In two-particle angular correlation measurements, jets give rise to a near-side peak, formed by particles associated to a higher-pT trigger particle. Measurements of these correlations as a function ...of pseudorapidity (Δη) and azimuthal (Δφ) differences are used to extract the centrality and pT dependence of the shape of the near-side peak in the pT range 1 < pT < 8 GeV/c in Pb-Pb and pp collisions at √sNN = 2.76 TeV. A combined fit of the near-side peak and long-range correlations is applied to the data and the peak shape is quantified by the variance of the distributions. And while the width of the peak in the Δφ direction is almost independent of centrality, a significant broadening in the Δη direction is found from peripheral to central collisions. This feature is prominent for the low-pT region and vanishes above 4 GeV/c. The widths measured in peripheral collisions are equal to those in pp collisions in the Δφ direction and above 3 GeV/c in the Δη direction. Furthermore, for the 10% most central collisions and 1 < pT,assoc < 2 GeV/c, 1 < pT,trig < 3 GeV/c, a departure from a Gaussian shape is found: a depletion develops around the center of the peak. Our results are compared to A Multi-Phase Transport (AMPT) model simulation as well as other theoretical calculations indicating that the broadening and the development of the depletion are connected to the strength of radial and longitudinal flow.
Here, 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 √sNN = 2.76 TeV. The measurements have been performed in the centrality range 0%–50% and for pion pair transverse momenta 0.2 < kT < 0.7 GeV/c. We find that the Rside and Rout 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 Rside oscillations, is found to be significantly smaller than the initial-state source eccentricity, but remains positive—indicating that even after a stronger expansion in the in-plane direction, the pion source at the freeze-out is still elongated in the out-of-plane direction. The 3+1D hydrodynamic calculations are in qualitative agreement with observed centrality and transverse momentum Rside oscillations, but systematically underestimate the oscillation magnitude.
The production of muons from heavy-flavour hadron decays in p–Pb collisions at √s NN =5.02 TeV was studied for 2 < p T < 16 GeV/c with the ALICE detector at the CERN LHC. The measurement was ...performed at forward (p-going direction) and backward (Pb-going direction) rapidity, in the ranges of rapidity in the centre-of-mass system (cms) 2.03 < y cms < 3.53 and -4.46 < y cms < -2.96, respectively. The production cross sections and nuclear modification factors are presented as a function of transverse momentum (p T ). At forward rapidity, the nuclear modification factor is compatible with unity while at backward rapidity, in the interval 2.5 < p T < 3.5 GeV/c, it is above unity by more than 2σ. The ratio of the forward-to-backward production cross sections is also measured in the overlapping interval 2.96 < |y cms | < 3.53 and is smaller than unity by 3.7σ in 2.5 < p T < 3.5 GeV/c. The data are described by model calculations including cold nuclear matter effects.
The creation of the CASTOR forward calorimeter in the compact muon spectrometer (CMS) experiment at the Large Hadron Collider (LHC), CERN enabled us to perform experiments at energies corresponding ...to those of cosmic rays but at much greater intensities, the most important factor in studying rare and anomalous phenomena.
The transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC in the range. ...The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb–Pb collisions at √sNN = 2.76 TeV.
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