1,483 research outputs found
Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV
No full textWe 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
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=5.02 TeV
No full textWe 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
K S 0 - and (anti-) Λ -hadron correlations in pp collisions at s = 13 TeV
No full textAbstract Two-particle Azimuthal correlations are measured with the ALICE apparatus in pp collisions at s = 13 TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson ( K S 0 ) or baryon ( Λ ) with transverse momentum p T > 3 GeV/ c is produced. Azimuthal correlations between kaons or Λ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger ( 3 < p T trigg < 20 GeV/ c ) and associated particle p T (1 GeV/ c < p T assoc < p T trigg ), for minimum-bias events and as a function of the event multiplicity. The near- and away-side peak yields are compared for the case of either K S 0 or Λ ( Λ ¯ ) being the trigger particle with that of inclusive hadrons (a sample dominated by pions). In addition, the measurements are compared with predictions from PYTHIA 8 and EPOS LHC event generators
Measurement of D-0, D+, D+* and D-s(+) production in pp collisions at root s=5.02 TeV with ALICE
No full textThe measurements of the production of prompt D0 , D+ , D∗+ , and D+s mesons in proton–proton (pp) col- lisions at √s = 5.02 TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity (|y| < 0.5) via their hadronic decay channels D0 → K−π+, D+ → K−π+π+, D∗+ → D0π+ → K−π+π+, D+s → φπ+ → K+K−π+, and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0 < pT < 36GeV/cforD0,1 < pT < 36GeV/cforD+ and D∗+, and in 2 < pT < 24 GeV/c for D+s mesons. Thanks to the higher integrated luminosity, an analysis in finer pT bins with respect to the previous measurements at √s = 7 TeV was performed, allowing for a more detailed description of the cross-section pT shape. The measured pT- differential production cross sections are compared to the results at √s = 7 TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combin- ing the ALICE and LHCb measurements in pp collisions at √s = 5.02 TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p–Pb and Pb–Pb collisions performed at the same nucleon– nucleon centre-of-mass energy
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
No full textElectrons 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
Neutral pion and η meson production in proton-proton collisions at s √ =0.9 TeV and s √ =7 TeV
No full textThe first measurements of the invariant differential cross sections of inclusive π0 and η meson production at mid-rapidity in proton–proton collisions at √ s = 0.9 TeV and √ s = 7 TeV are reported. The π0 measurement covers the ranges 0.4 <pT <7 GeV/c and 0.3 <pT <25 GeV/c for these two energies, respectively. The production of η mesons was measured at √ s = 7 TeV in the range 0.4 <pT <15 GeV/c. Next-to-Leading Order perturbative QCD calculations, which are consistent with the π0 spectrum at √ s = 0.9 TeV, overestimate those of π0 and η mesons at √ s = 7 TeV, but agree with the measured η/π0 ratio at √ s =7 TeV
Production of muons from heavy-flavour hadron decays in pp collisions at √s = 5.02 TeV s = 5.02 TeV
No full textProduction cross sections of muons from semi-leptonic decays of charm and beauty hadrons were measured at forward rapidity (2.5 < y < 4) in proton-proton (pp) collisions at a centre-of-mass energy √s = 5.02 TeV with the ALICE detector at the CERN LHC. The results were obtained in an extended transverse momentum interval, 2 < pT < 20 GeV/c, and with an improved precision compared to previous measurements performed in the same rapidity interval at centre-of-mass energies√s = 2.76 and 7 TeV. The pT- and y-differential production cross sections as well as the pT-differential production cross section ratios between different centre-of-mass energies and different rapidity intervals are described, within experimental and theoretical uncertainties, by predictions based on perturbative QCD
Lambda K femtoscopy in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textThe first measurements of the scattering parameters of Lambda K pairs in all three charge combinations (Lambda K+, Lambda K-, and Lambda K-S(0)) are presented. The results are achieved through a femtoscopic analysis of Lambda K correlations in Pb-Pb collisions at root s(NN) = 2.76 TeV recorded by ALICE at the Large Hadron Collider. The femtoscopic correlations result from strong final-state interactions and are fit with a parametrization allowing for both the characterization of the pair emission source and the measurement of the scattering parameters for the particle pairs. Extensive studies with the THERMINATOR 2 event generator provide a good description of the nonfemtoscopic background, which results mainly from collective effects, with unprecedented precision. Furthermore, together with HIJING simulations, this model is used to account for contributions from residual correlations induced by feed-down from particle decays. The extracted scattering parameters indicate that the strong force is repulsive in the Lambda K+ interaction and attractive in the Lambda K- interaction. The data hint that the Lambda K-S(0) interaction is attractive; however, the uncertainty of the result does not permit such a decisive conclusion. The results suggest an effect arising either from different quark-antiquark interactions between the pairs (s (s) over bar in Lambda K+ and u (u) over bar in Lambda K-) or from different net strangeness for each system (S = 0 for Lambda K+, and S = -2 for Lambda K-). Finally, the Lambda K systems exhibit source radii larger than expected from extrapolation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle Lambda and K source distributions
K-S(0) and Lamda Production in Pb-Pb Collisions at root s(NN)=2:76??TeV
No full textThe ALICE measurement of K and production at mid-rapidity in Pb-Pb collisions at = 2.76 TeV is presented. The transverse momentum () spectra are shown for several collision centrality intervals and in the range from 0.4 GeV/c (0.6 GeV/c for ) to 12 GeV/c. The dependence of the ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate pT is not observed in pp interactions at = 0.9 TeV and at = 7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of , models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the dependence of the ratio.The ALICE measurement of KS0 and Λ production at midrapidity in Pb-Pb collisions at sNN=2.76 TeV is presented. The transverse momentum (pT) spectra are shown for several collision centrality intervals and in the pT range from 0.4 GeV/c (0.6 GeV/c for Λ) to 12 GeV/c. The pT dependence of the Λ/KS0 ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher pT with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate pT is not observed in pp interactions at s=0.9 TeV and at s=7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured pT spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of pT, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the pT dependence of the Λ/KS0 ratio.The ALICE measurement of K and production at mid-rapidity in Pb-Pb collisions at TeV is presented. The transverse momentum () spectra are shown for several collision centrality intervals and in the range from 0.4 GeV/ (0.6 GeV/ for ) to 12 GeV/. The dependence of the /K ratios exhibits maxima in the vicinity of 3 GeV/, and the positions of the maxima shift towards higher with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate is not observed in pp interactions at sqrt(s) = 0.9 TeV and at sqrt(s) = 7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured spectra above 2 GeV/ progressively decouple from hydrodynamical-model calculations. For higher values of , models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the dependence of the /K ratio
Pseudorapidity distributions of charged particles as a function of mid- and forward rapidity multiplicities in pp collisions at s = 5.02, 7 and 13 TeV
No full textAbstract The multiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies s = 5.02 , 7 and 13 TeV measured by ALICE is reported. The analysis relies on track segments measured in the midrapidity range ( | η | < 1.5 ). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval | η | < 1 . The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions
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