Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Pseudorapidity densities of charged particles with transverse momentum thresholds in pp collisions at √ s = 5.02 and 13 TeV

The pseudorapidity density of charged particles with minimum transverse momentum (pT) thresholds of 0.15, 0.5, 1, and 2 GeV/c is measured in pp collisions at the center of mass energies of √s=5.02 and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity (η) within 0.8pT larger than the corresponding threshold. In addition, measurements without pT-thresholds are performed for inelastic and nonsingle-diffractive events as well as for inelastic events with at least one charged particle having |η|2GeV/c), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at √s=13TeV.

Multiharmonic Correlations of Different Flow Amplitudes in Pb-Pb Collisions at sNN=2.76\sqrt{s_{_{NN}}}=2.76 TeV

The event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions, using higher-order symmetric cumulants. We find that different three-harmonic correlations develop during the collective evolution of the medium when compared to correlations that exist in the initial state. These new results cannot be interpreted in terms of previous lower-order flow measurements since contributions from two-harmonic correlations are explicitly removed in the new observables. A comparison to Monte Carlo simulations provides new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions

Measuring KS0^0_{\rm S}K±^{\rm \pm} interactions using Pb-Pb collisions at sNN=2.76{\sqrt{s_{\rm NN}}=2.76} TeV

We present the first ever measurements of femtoscopic correlations between the KS0 and K ± particles. The analysis was performed on the data from Pb–Pb collisions at sNN=2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a0(980) resonance. The extracted kaon source radius and correlation strength parameters for KS0K− are found to be equal within the experimental uncertainties to those for KS0K+ . Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a0 resonance are tested. Our results are also compatible with the interpretation of the a0 having a tetraquark structure instead of that of a diquark

Measurement of D-meson production at mid-rapidity in pp collisions at s=7{\sqrt{s}=7} TeV

The production cross sections for prompt charmed mesons $\mathrm{D^0}$ , $\mathrm{D^+}$ , $\mathrm{D^{*+}}$ and $\mathrm{D_s^+}$ were measured at mid-rapidity in proton–proton collisions at a centre-of-mass energy $\sqrt{s}=7~{\mathrm {TeV}}$ with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays $\mathrm{D}^0 \rightarrow \mathrm{K}^-\pi ^+$ , $\mathrm{D}^+\rightarrow \mathrm{K}^-\pi ^+\pi ^+$ , $\mathrm{D}^{*+} \rightarrow \mathrm{D}^0 \pi ^+$ , $\mathrm{D_s^{+}\rightarrow \phi \pi ^+\rightarrow K^-K^+\pi ^+}$ , and their charge conjugates.With respect to previous measurements in the same rapidity region, the coverage in transverse momentum ( $p_\mathrm{T}$ ) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total $\mathrm{c}{\overline{\mathrm{c}}}$ production cross section is likewise improved. The measured $p_\mathrm{T}$ -differential cross sections are compared with the results of three perturbative QCD calculations

Long- and short-range correlations and their event-scale dependence in high-multiplicity pp collisions at s=13\boldsymbol{\sqrt{{\textit s}}}=13 TeV

Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at $\sqrt{s}$ = 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-(∆η ∼ 0) and long-range (1.6 < |∆η| < 1.8) in pseudorapidity are extracted on the near-side (∆φ ∼ 0). They are reported as a function of transverse momentum (p$_{T}$) in the range 1 < p$_{T}$< 4 GeV/c. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-p$_{T}$ leading particles or jets for varying p$_{T}$ thresholds. The results demonstrate that the long-range “ridge” yield, possibly related to the collective behavior of the system, is present in events with high-p$_{T}$ processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the p$_{T}$ dependency, while overestimating the event-scale dependency