270 research outputs found
Prompt charm production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
No full textCharm production at the LHC in pp collisions at s√=7 TeV is studied with the LHCb detector. The decays D0→K−π+, D+→K−π+π+, D⁎+→D0(K−π+)π+, D+s→ϕ(K−K+)π+, Λ+c→pK−π+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb−1. Differential cross-sections dσ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0<pT<8 GeV/c and 2.0<y<4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives
σ(cc¯)pT<8 GeV/c,2.0<y<4.5=1419±12(stat)±116(syst)±65(frag) μb,
where the uncertainties are statistical, systematic, and due to the fragmentation functions
Beauty production in pp collisions at root s=2.76 TeV measured via semi-electronic decays
No full textThe ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y| < 0.8 and transverse momentum 1 < p(T)< 10 GeV/c, in pp collisions at root s = 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, sigma(b -> e) = 3.47 +/- 0.40(stat)(+1.12)(-1.33)(sys) +/- 0.07(norm) mu b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total b (b) over bar production cross section, sigma(b (b) over bar) = 130 +/- 15.1(stat)(+42.1)(-49.8)(sys)(+3.4)(-3.1)(extr) +/- 2.5(norm) +/- 4.4(BR) mu b. (C) 2014 The Authors. Published by Elsevier B.
Lambda and (Lambda)over-bar polarization in Au-Au collisions at RHIC
No full textExperiments at RHIC have shown that in 200 GeV Au-Au collisions, the Lambda and (Lambda) over bar hyperons are produced with very small polarizations (Abelev et al., 2007) [1], almost consistent with zero. These results can be understood in terms of a model that we proposed (Barros and Hama, 2008) [2]. In this Letter, we show how this model may be applied in such collisions, and also will discuss the relation of our results with other models, in order to explain the experimental data. (C) 2011 Elsevier B.V. All rights reserved.FAPESCFundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina (FAPESC
Measurement of quarkonium production at forward rapidity in collisions at TeV
No full textThe inclusive production cross sections at forward rapidity of , , (1S) and (2S) are measured in collisions at with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pb. Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum and rapidity , over the ranges GeV/c for , GeV/c for all other resonances and for . The measured cross sections integrated over and , and assuming unpolarized quarkonia, are: b, b, nb and nb, where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models
Suppression of high transverse momentum D mesons in central Pb-Pb collisions at √sNN= 2.76 TeV
No full textThe production of the prompt charm mesons D0, D+, D∗+, and their antiparticles,
was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a
centre-of-mass energy √sNN = 2.76 TeV per nucleon-nucleon collision. The pt-differential
production yields in the range 2 < pt < 16 GeV/c at central rapidity, |y| < 0.5, were used
to calculate the nuclear modification factor RAA with respect to a proton-proton reference
obtained from the cross section measured at √s = 7 TeV and scaled to √s = 2.76 TeV. For
the three meson species, RAA shows a suppression by a factor 3–4, for transverse momenta
larger than 5 GeV/c in the 20% most central collisions. The suppression is reduced for
peripheral collisions
Azimuthal anisotropy of D-meson production in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textThe production of the prompt charmed mesonsD(0), D+, andD(*+) relative to the reaction plane was measured in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of root s(NN) = 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (pT) interval 2-16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v(2) in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor R-AA, measured in the direction of the reaction plane and orthogonal to it. The v(2) coefficient was measured with three different methods and in three centrality classes in the interval 0%-50%. A positive v(2) is observed in midcentral collisions (30%-50% centrality class), with a mean value of 0.204(-0.036)(+0.099) (tot.unc.) in the interval 2 < pT < 6 GeV/c, which decreases towards more central collisions (10%-30% and 0%-10% classes). The positive v(2) is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane formidcentral collisions. The measurements are compared to theoretical calculations of charm-quark transport and energy loss in high-density strongly interacting matter at high temperature. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. However, they are challenged to simultaneously describe the strong suppression of high-pT yield of D mesons in central collisions and their azimuthal anisotropy in noncentral collision
Beauty production in pp collisions at root s=2.76 TeV measured via semi-electronic decays
No full textThe ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y| LT 0.8 and transverse momentum 1 LT p(T) LT 10 GeV/c, in pp collisions at root s = 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, sigma(b - GT e) = 3.47 +/- 0.40(stat)(+1.12)(-1.33)(sys) +/- 0.07(norm) mu b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total b (b) over bar production cross section, sigma(b (b) over bar) = 130 +/- 15.1(stat)(+42.1)(-49.8)(sys)(+3.4)(-3.1)(extr) +/- 2.5(norm) +/- 4.4(BR) mu b. (C) 2014 The Authors. Published by Elsevier B.V
Upgrade of the ALICE Experiment Letter Of Intent
No full textThis Letter of Intent (LoI) presents the plans of the ALICE (A Large Ion Collider Experiment [1]) collaboration to
extend its physics programme, in order to fully exploit the scientific potential of the Large Hadron Collider (LHC)
for fundamental studies of QCD, with the main emphasis on heavy-ion collisions. The proposed enhancement of
the ALICE detector performance will enable detailed and quantitative characterization of the high density, high
temperature phase of strongly interacting matter, together with the exploration of new phenomena in QCD. In
the following we outline the physics motivation for running the LHC with heavy ions at high luminosities and
summarize the performance gains expected with the upgraded ALICE detector. With the proposed timeline of
initiating high-rate operation after the 2018 Long Shutdown (LS2), the objectives of our upgrade plans will be
achieved by collecting data into the mid-2020’s
Measurement of Prompt D-Meson Production in p-Pb Collisions at root s(NN)=5.02 TeV
No full textThe p(T)-differential production cross sections of the prompt charmed mesons D-0, D+, D*(-), and D-s(+) and their charge conjugate in the rapidity interval -0.96 < y(cms) < 0.04 were measured in p-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R-pPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1 < p(T) < 24 GeV/c. No significant difference among the R-pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter
Measurement of charm production at central rapidity in proton-proton collisions at square s = 2.76 TeV
No full textThe p(t)-differential production cross sections of the prompt (B feed-down subtracted) charmed mesons D-0, D+, and D*(+) in the rapidity range vertical bar y vertical bar LT 0.5, and for transverse momentum 1 LT p(t) LT 12 GeV/c, were measured in proton-proton collisions at root s = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The analysis exploited the hadronic decays D-0 - GT K-pi(+), D+ - GT K-pi(+)pi(+), D*(+) - GT D-0 pi(+), and their charge conjugates, and was performed on a L-int = 1.1 nb(-1) event sample collected in 2011 with a minimum-bias trigger. The total charm production cross section at root s = 2.76 TeV and our previous measurements at root s = 7 TeV. The results were compared to existing measurements and to perturbative-QCD calculations. The fraction of c(d)over-bar D mesons produced in a vector state was also determined
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