86 research outputs found

    Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV

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    We present the first ever measurements of femtoscopic correlations between the K-S(0) and K-+/- particles. The analysis was performed on the data from Pb-Pb collisions at root S-NN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a(0) resonance are tested. Our results are also compatible with the interpretation of the a(0) having a tetraquark structure instead of that of a diquark. (c) 2017 The Author. Published by Elsevier B.V

    Measurement of the production of high-p(T) electrons from heavy-flavour hadron decays in Pb-Pb collisions at root s(NN)=2.76 TeV

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    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 root s(NN) = 2.76 TeV. The transverse momentum (pT) 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. (C) 2017 The Author. Published by Elsevier B.V

    Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=5.02 TeV

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    We present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V

    First measurement of Xi(0)(c) production in pp collisions at root s=7 TeV

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    The production of the charm-strange baryon Xi(0)(c) is measured for the first time at the LHC via its semileptonic decay into e(+) Xi(-) nu(e) in ppcollisions at root s = 7 TeV with the ALICE detector. The transverse momentum ( p(T)) differential cross section multiplied by the branching ratio is presented in the interval 1 < p(T)< 8 GeV/c at mid-rapidity, vertical bar y vertical bar < 0.5. The transverse momentum dependence of the Xi(0)(c) baryon production relative to the D-0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio. (C) 2018 The Author(s). Published by Elsevier B.V

    J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=5.02 TeV

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    We report a precise measurement of the J/psi elliptic flow in Pb-Pb collisions at root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The J/psi mesons are reconstructed at midrapidity (|y| < 0.9) in the dielectron decay channel and at forward rapidity (2.5 < y < 4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v(2) of the J/psi is studied as a function of the transverse momentum and centrality. A positive v(2) is observed in the transverse momentum range 2<p(T)<8GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at root s(NN) = 2.76 TeV in semicentral collisions. At midrapidity, the J/psi v(2) is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low p(T) the elliptic flow of the J/psi originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models

    Measurement of charm production at central rapidity in proton proton collisions at sqrt{s}=2.76 TeV

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    Measurement of the Cross Section for Electromagnetic Dissociation with Neutron Emission in Pb-Pb Collisions at root s(NN)=2.76 TeV

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    The first measurement of neutron emission in electromagnetic dissociation of Pb-208 nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at root s(NN) = 2.76 TeV with neutron emission are sigma(singleEMD) = 187.4 +/- 0.2(stat)(-11.2)(+13.2) (syst) b and sigma(mutualEMD) = 5. 7 +/- 0.1(stat) +/- 0.4(syst) b, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model. DOI: 10.1103/PhysRevLett.109.252302 Times Cited: 17 (from All Databases) [Remove this record from the Marked List.] 2

    Erratum to: Production of pi(0) and eta mesons up to high transverse momentum in pp collisions at 2.76 TeV (vol 77, 339, 2017)

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    Production of pi(0) and eta mesons up to high transverse momentum in pp collisions at 2.76 TeV

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    The invariant differential cross sections for inclusive pi(0) and eta mesons at midrapidity were measured in pp collisions at root s = 2.76 TeV for transverse momenta 0.4 < pT < 40 GeV/c and 0.6 < pT < 20 GeV/c, respectively, using the ALICE detector. This large range in pT was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a newsingle-cluster, shower-shape based method was developed for the identification of high-pT neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the pi(0), and between 30-50% for the. meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10-30%, except at pT < 1 GeV/c. The new data can therefore be used to further improve the theoretical description of pi(0) and eta meson production

    Kaon femtoscopy in Pb-Pb collisions at root s(NN)=2.76 TeV

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    We present the results of three-dimensional femtoscopic analyses for charged and neutral kaons recorded by ALICE in Pb-Pb collisions at root s(NN) = 2.76 TeV. Femtoscopy is used to measure the space-time characteristics of particle production from the effects of quantum statistics and final-state interactions in two-particle correlations. Kaon femtoscopy is an important supplement to that of pions because it allows one to distinguish between different model scenarios working equally well for pions. In particular, we compare the measured three-dimensional kaon radii with a purely hydrodynamical calculation and a model where the hydrodynamic phase is followed by a hadronic rescattering stage. The former predicts an approximate transverse mass (m(T)) scaling of source radii obtained from pion and kaon correlations. This m(T) scaling appears to be broken in our data, which indicates the importance of the hadronic rescattering phase at LHC energies. A k(T) scaling of pion and kaon source radii is observed instead. The time of maximal emission of the system is estimated by using the three-dimensional femtoscopic analysis for kaons. The measured emission time is larger than that of pions. Our observation is well supported by the hydrokinetic model predictions
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