Measurement of transverse energy at midrapidity in Pb-Pb collisions at root s(NN)=2.76 TeV

We report the transverse energy (ET) measured with ALICE at midrapidity in Pb-Pb collisions at root s(NN) = 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 (eta), , in 0%-5% central collisions is 1737 +/- 6(stat.) +/- 97(sys.) GeV. We find a similar centrality dependence of the shape of as a function of the number of participating nucleons to that seen at lower energies. The growth in at the LHC energies exceeds extrapolations of low-energy data. We observe a nearly linear scaling of with the number of quark participants. With the canonical assumption of a 1 fm/c formation time, we estimate that the energy density in 0%-5% central Pb-Pb collisions at root s(NN) = 2.76 TeV is 12.3 +/- 1.0 GeV/fm(3) and that the energy density at the most central 80 fm(2) of the collision is at least 21.5 +/- 1.7 GeV/fm(3). This is roughly 2.3 times that observed in 0%-5% central Au-Au collisions at root s(NN) = 200 GeV.Peer reviewe

phi-Meson production at forward rapidity in p-Pb collisions at root s(NN)=5.02 TeV and in pp collisions at root s=2.76 TeV

The first study of phi-meson production in p-Pb collisions at forward and backward rapidity, at a nucleonnucleon centre-of-mass energy root s(NN)= 5.02 TeV, has been performed with the ALICE apparatus at the LHC. The phi-mesons have been identified in the dimuon decay channel in the transverse momentum (p(T)) range 1 <p(T) <7GeV/c, both in the p-going (2.03 <y <3.53) and the Pb-going (-4.46 <y <-2.96) directions - where ystands for the rapidity in the nucleon-nucleon centre-of-mass - the integrated luminosity amounting to 5.01 +/- 0.19nb(-1) and 5.81 +/- 0.20nb(-1), respectively, for the two data samples. Differential cross sections as a function of transverse momentum and rapidity are presented. The forward-backward ratio for f-meson production is measured for 2.96Peer reviewe

Azimuthally Differential Pion Femtoscopy in Pb-Pb Collisions at root s(NN)=2.76 TeV

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 root(NN)-N-s = 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 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 R-side oscillations, but systematically underestimate the oscillation magnitude.Peer reviewe

J/Psi suppression at forward rapidity in Pb-Pb collisions at root s(NN)=5.02 TeV

The inclusive J/Psi production has been studied in Pb-Pb and pp collisions at the centre-of-mass energy per nucleon pair root sNN= 5.02TeV, using the ALICE detector at the CERN LHC. The J/Psi meson is reconstructed, in the centre-of-mass rapidity interval 2.5 <y <4and in the transverse- momentum range p(T)<12GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/Psi cross section in pp collisions at root s= 5.02TeV and on the nuclear modification factor R-AA. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum p(T) of the J/Psi. The measured R-AA values indicate a suppression of the J/Psi in nuclear collisions and are then compared to our previous results obtained in Pb-Pb collisions at root sNN= 2.76TeV. The ratio of the R-AA values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10% centrality) is 1.17 +/- 0.04( stat)+/- 0.20(syst). In central events, as a function of p(T), a slight increase of R-AA with collision energy is visible in the region 2 <p(T)<6GeV/c. Theoretical calculations qualitatively describe the measurements, within uncertainties. (C) 2017 The Author. Published by Elsevier B.V.Peer reviewe

Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at root s(NN)=2.76 TeV

Peer reviewe

Multipion Bose-Einstein correlations in pp, p-Pb, and Pb-Pb collisions at energies available at the CERN Large Hadron Collider

Peer reviewe

Measurement of pion, kaon and proton production in proton-proton collisions at sqrt(s) = 7 TeV

The measurement of primary $$\pi ^\pm$$ϱ, $$K^\pm$$K±, $$p$$p and \overlinepp¯ production at mid-rapidity ($$|y| <$$|y|< 0.5) in protonâproton collisions at \sqrtss$$=$$= 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/$$c$$c for pions, from 0.2 up to 6 GeV/$$c$$c for kaons and from 0.3 up to 6 GeV/$$c$$c for protons. The measured spectra and particle ratios are compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies

Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC

We present the first measurement of the two-particle transverse momentum differential correlation function, P-2 = / (2), in Pb-Pb collisions at root s(NN) = 2.76 TeV. Results for P-2 are reported as a function of the relative pseudorapidity (Delta eta) and azimuthal angle (Delta phi) between two particles for different collision centralities. The Delta phi dependence is found to be largely independent of Delta eta for broken vertical bar Delta eta broken vertical bar >= 0.9. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around Delta phi=pi (i. e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of P-2, studied as a function of the collision centrality, show that correlations at broken vertical bar Delta eta broken vertical bar >= 0.9 can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system

Charge correlations using the balance function in Pb–Pb collisions at √sNN =2.76 TeV

In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity (∆η) and azimuthal angle (∆φ) in Pb–Pb collisions at √sNN =2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in ∆φ but fails to describe the correlations in ∆η. A thermal blast-wave model incorporating local charge conservation and tuned to describe the pT spectra and v2 measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with √sNN: the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in ∆η and ∆φ with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision

Measurement of pion, kaon and proton production in proton-proton collisions at sqrt(s) = 7 TeV

The measurement of primary $$\pi ^\pm$$ϱ, $$K^\pm$$K±, $$p$$p and \overlinepp¯ production at mid-rapidity ($$|y| <$$|y|< 0.5) in protonâproton collisions at \sqrtss$$=$$= 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/$$c$$c for pions, from 0.2 up to 6 GeV/$$c$$c for kaons and from 0.3 up to 6 GeV/$$c$$c for protons. The measured spectra and particle ratios are compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies