41 research outputs found

    f(0)(980) resonance production in pp collisions with the ALICE detector at the LHC

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    We report on a preliminary study of the production of f(0)(980) -> pi(+)pi(-) at mid-rapidity (vertical bar y vertical bar < 0.5) performed with the ALICE detector at the LHC in minimum bias pp collisions at the centre-of-mass energy root s = 5.02 TeV. The f(0)(980) signal extraction is challenging due to the large background from correlated pi(+)pi(-) pairs from other resonance decays in the invariant mass window under study, as well as due to the combinatorics from uncorrelated pairs. We present the strategy for the signal extraction and first results in terms of p(T)-dependent production yields. The results are discussed and compared with production yields of other resonances and stable hadrons

    Lambda(+)(C) production in pb-pb collisions at root S-NN=5.02 TeV

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    AA measurement of the production of prompt Λ c + baryons in Pb–Pb collisions at s NN =5.02 TeV with the ALICE detector at the LHC is reported. The Λ c + and Λ ̅ c − were reconstructed at midrapidity (|y|&lt;0.5) via the hadronic decay channel Λ c + →pK S 0 (and charge conjugate) in the transverse momentum and centrality intervals

    Non-linear flow modes of identified particles in Pb-Pb collisions at root s(NN)=5.02 TeV with the ALICE detector

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    The non-linear flow modes, v(4,22), v(5,32) and v(6,33) as a function of transverse momentum (p(T)) have been measured for the first time in Pb-Pb collisions at root s(NN) = 5.02 TeV for identified particles, i.e. charged pions, kaons and (anti-)protons. These observables probe the contribution of the second and third initial anisotropy coefficients to the higher order flow harmonics. Interestingly, all the characteristic features observed in previous p(T)-differential as well as p(T)-integrated measurements (e.g. v(2) and v(3)) for various particle species are present in these measurements, i.e. increase of magnitude with increasing centrality percentile, a mass ordering in the low p(T) region and a particle type grouping in the intermediate p(T) region. The results cover 0-1\% (ultra-central collisions), 10-20\% (mid-central collisions) and 40-50\% (mid-peripheral collisions) centrality intervals and allow to test models that attempt to describe initial conditions and the mode-coupling of different harmonics

    Transverse momentum spectra and nuclear modification factors of charged particles in Xe–Xe collisions at sNN=5.44TeV

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    Transverse momentum (pT) spectra of charged particles at mid-pseudorapidity in Xe–Xe collisions at √sNN = 5.44 TeV measured with the ALICE apparatus at the Large Hadron Collider are reported. The kinematic range 0.15 < pT < 50 GeV/c and |η| < 0.8 is covered. Results are presented in nine classes of collision centrality in the 0–80% range. For comparison, a pp reference at the collision energy of √s = 5.44 TeV is obtained by interpolating between existing pp measurements at √s = 5.02 and 7 TeV. The nuclear modification factors in central Xe–Xe collisions and Pb–Pb collisions at a similar center-of- mass energy of √sNN = 5.02 TeV, and in addition at 2.76 TeV, at analogous ranges of charged particle multiplicity density ⟨dNch/dη⟩ show a remarkable similarity at pT > 10 GeV/c. The centrality dependence of the ratio of the average transverse momentum ⟨pT⟩ in Xe–Xe collisions over Pb–Pb collision at √s = 5.02 TeV is compared to hydrodynamical model calculations

    Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV

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    The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton–proton (pp) collisions at a centre-of-mass energy √s = 13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at √s = 7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc ̄/dy|y=0 = 974 ± 138(stat.) ± 140(syst.) ± 214(BR) μb and dσbb ̄/dy|y=0 =79±14(stat.)±11(syst.)±5(BR) μb using PYTHIA simulations and dσcc ̄/dy|y=0 = 1417 ± 184(stat.) ± 204(syst.) ± 312(BR) μb and dσbb ̄/dy|y=0 = 48 ± 14(stat.) ± 7(syst.) ± 3(BR) μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations

    Measurements of anisotropic flow and flow fluctuations in Xe-Xe and Pb-Pb collisions with ALICE

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    Anisotropic flow is a key observable to characterise the system created in heavy-ion collisions, as it is sensitive to the system's initial state, transport properties, the equation of state and freeze-out conditions. In these proceedings we present the anisotropic flow coefficients of inclusive charged particles in Pb-Pb collisions at root s(NN) = 2.76 and 5.02 TeV, and in Xe-Xe collisions at root s(NN) = 5.44 TeV. The results are reported for a wide range of particle transverse momentum within the pseudo-rapidity range vertical bar eta vertical bar < 0.8 at different collision centralities. The energy and system dependence are found to place strong constraints on the temperature dependence of eta/s and the modeling of the initial state, respectively. We also present detailed studies of flow fluctuations in heavy-ion collisions, in order to precisely characterise the underlying flow probability density function. We find evidence of non-Bessel-Gaussian fluctuations and discuss the origin of this observation

    Coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV

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    The ALICE Collaboration has made the first measurement at the LHC of J/psi photoproduction in ultra-peripheral Pb-Pb collisions at root s(NN) = 2.76 TeV. The J/psi is identified via its dimuon decay in the forward rapidity region with the muon spectrometer for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 55 mu b(-1). The cross section for coherent J/psi production in the rapidity interval -3.6 < y < -2.6 is measured to be d sigma(coh)(J/psi)/dy = 1.00 +/- 0.18(stat)(-0.26)(+0.24)(syst) mb. The result is compared to theoretical models for coherent J/psi production and found to be in good agreement with those models which include nuclear gluon shadowing. (C) 2012 CERN. Published by Elsevier B.V. All rights reserve

    Constraining production models with light (anti-)nuclei measurements in small systems with ALICE at the LHC

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    The production of deuterons and anti-deuterons in pp collisions at root s = 7 and 13 TeV has been studied as a function of charged-particle multiplicity using the ALICE detector at the LHC. The preliminary results are shown here, together with those obtained in heavy-ion collisions. They are presented by focusing the discussion on the comparison with expectations from hadron-coalescence models

    Investigating correlated fluctuations of conserved charges with net-A fluctuations in Pb-Pb collisions at ALICE

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    Event-by-event fluctuations of conserved charges such as electric charge, strangeness, and baryon number - in ultrarelativistic heavy-ion collisions provide insight into the properties of the quark-gluon plasma and the QCD phase diagram. They can be related to the higher moments of the multiplicity distributions of identified particles, such as the A baryon which carries both strangeness and baryon number and is thus of particular interest. We present the first measurement of net-A fluctuations in Pb-Pb collisions at root s(NN)=5.02 TeV as a function of centrality and the pseudorapidity acceptance of the measurement. The results are compared to expectations of the effects of global baryon number conservation as well as to predictions from the HIJING Monte Carlo event generator. In this analysis the Identity Method is applied in a novel way to account for the combinatoric background in the invariant mass distribution

    Pion-kaon femtoscopy in Pb-Pb collisions at root s(NN)=2.76 TeV measured with ALICE

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    Femtoscopic correlations between charged pions and kaons for different charge combinations are measured in Pb-Pb collisions at root s(NN) = 2.76 TeV with ALICE at the LHC. The three-dimensional pion-kaon (pi - K) correlation functions and double ratios in the out-side-long pair rest frame are studied in different centrality bins. The pi - K femtoscopic source size parameter (R-out) and emission asymmetry (mu(out)) are extracted. It is observed that the average source size of the system and the emission asymmetry between pions and kaons increase from peripheral to central events
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