272 research outputs found
Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in PbāPb collisions at sNN=2.76TeV
This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators G2CI and G2CD in PbāPb collisions at sNN=2.76TeV by the ALICE collaboration. The two-particle transverse momentum correlator G2 was introduced as a measure of the momentum current transfer between neighboring system cells. The correlators are measured as a function of pair separation in pseudorapidity (ĪĪ·) and azimuth (ĪĻ) and as a function of collision centrality. From peripheral to central collisions, the correlator G2CI exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, G2CD exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density Ī·/s of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of Ī·/s and is in qualitative agreement with values obtained from anisotropic flow measurements
A model of a small open economy integrated in a monetary union
This paper develops a model of a small open economy integrated in a monetary union, which is a nontrivial technical extension of the existing small open economy model. The model is used to study the monetary transmission mechanism in Portugal.info:eu-repo/semantics/publishedVersio
Production of light-flavor hadrons in pp collisions at ās=7andās=13TeV
The production of ĻĀ±, K Ā±, KS0, K ā(892) , p , Ļ(1020) , Ī , Ī -, Ī© -, and their antiparticles was measured in inelastic protonāproton (pp) collisions at a center-of-mass energy of s = 13 TeV at midrapidity (| y| < 0.5) as a function of transverse momentum (pT) using the ALICE detector at the CERN LHC. Furthermore, the single-particle pT distributions of KS0, Ī , and Ī ĀÆ in inelastic pp collisions at s=7Ā TeV are reported here for the first time. The pT distributions are studied at midrapidity within the transverse momentum range 0 ā¤ pTā¤ 20 GeV/c, depending on the particle species. The pT spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower s and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high pT with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and xTā”2pT/s scaling properties of hadron production are also studied. As the collision energy increases from s = 7ā13Ā TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of s, while ratios for multi-strange hadrons indicate enhancements. The pT-differential cross sections of ĻĀ±, K Ā± and p (p ĀÆ) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for ĻĀ± and p (p ĀÆ) at high pT
Production of the Ļ(770)0 meson in pp and Pb-Pb collisions at sNN =2.76 TeV
The production of the Ļ(770)0 meson has been measured at midrapidity (|y|<0.5) in pp and centrality differential Pb-Pb collisions at sNN= 2.76 TeV with the ALICE detector at the Large Hadron Collider. The particles have been reconstructed in the Ļ(770)0āĻ+Ļ- decay channel in the transverse-momentum (pT) range 0.5-11 GeV/c. A centrality-dependent suppression of the ratio of the integrated yields 2Ļ(770)0/(Ļ++Ļ-) is observed. The ratio decreases by ā¼40% from pp to central Pb-Pb collisions. A study of the pT-differential 2Ļ(770)0/(Ļ++Ļ-) ratio reveals that the suppression occurs at low transverse momenta, pT<2 GeV/c. At higher momentum, particle ratios measured in heavy-ion and pp collisions are consistent. The observed suppression is very similar to that previously measured for the Kā(892)0/K ratio and is consistent with EPOS3 predictions that may imply that rescattering in the hadronic phase is a dominant mechanism for the observed suppression
Dielectron production in proton-proton collisions at ās=7 TeV
The first measurement of e(+)e(-) pair production at mid-rapidity (vertical bar eta vertical bar(e) < 0.8) in pp collisions at root s = 7TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (m(ee )< 3.3 GeV/c(2)), the pair transverse momentum (p(T,ee) < 8 GeV/c), and the pair transverse impact parameter (DCA(ee)), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < m(ee) < 1.1 GeV/c(2)), prompt and non-prompt e(+)e(-) sources can be separated via the DCA(ee). In the intermediate-mass region (1.1 < m(ee) < 2.7 GeV/c(2)), a double-differential fit to the data in m(ee) and p(T,ee) and a fit of the DCA(ee) distribution allow the total cc and bb cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional m(ee) and p(T,ee) spectra, as well as the shape , of the DCA(ee) distribution, reasonably well. However, differences in the c (c) over bar and b (b) over bar cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < p(T) < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations
Multiplicity dependence of (anti-)deuteron production in pp collisions at s=7TeV
In this letter, the production of deuterons and anti-deuterons in pp collisions at s=7 TeV is studied as a function of the charged-particle multiplicity density at mid-rapidity with the ALICE detector at the LHC. Production yields are measured at mid-rapidity in five multiplicity classes and as a function of the deuteron transverse momentum (pT). The measurements are discussed in the context of hadronācoalescence models. The coalescence parameter B2, extracted from the measured spectra of (anti-)deuterons and primary (anti-)protons, exhibits no significant pT-dependence for pT<3 GeV/c, in agreement with the expectations of a simple coalescence picture. At fixed transverse momentum per nucleon, the B2 parameter is found to decrease smoothly from low multiplicity pp to PbāPb collisions, in qualitative agreement with more elaborate coalescence models. The measured mean transverse momentum of (anti-)deuterons in pp is not reproduced by the Blast-Wave model calculations that simultaneously describe pion, kaon and proton spectra, in contrast to central PbāPb collisions. The ratio between the pT-integrated yield of deuterons to protons, d/p, is found to increase with the charged-particle multiplicity, as observed in inelastic pp collisions at different centre-of-mass energies. The d/p ratios are reported in a wide range, from the lowest to the highest multiplicity values measured in pp collisions at the LHC
Measurement of the (anti-)3He elliptic flow in PbāPb collisions at sNN=5.02TeV
The elliptic flow (v2) of (anti-)3He is measured in PbāPb collisions at sNN=5.02TeV in the transverse-momentum (pT) range of 2ā6 GeV/c for the centrality classes 0ā20%, 20ā40%, and 40ā60% using the event-plane method. This measurement is compared to that of pions, kaons, and protons at the same center-of-mass energy. A clear mass ordering is observed at low pT, as expected from relativistic hydrodynamics. The violation of the scaling of v2 with the number of constituent quarks at low pT, already observed for identified hadrons and deuterons at LHC energies, is confirmed also for (anti-)3He. The elliptic flow of (anti-)3He is underestimated by the Blast-Wave model and overestimated by a simple coalescence approach based on nucleon scaling. The elliptic flow of (anti-)3He measured in the centrality classes 0ā20% and 20ā40% is well described by a more sophisticated coalescence model where the phase-space distributions of protons and neutrons are generated using the iEBE-VISHNU hybrid model with AMPT initial conditions
Analysis of the apparent nuclear modification in peripheral PbāPb collisions at 5.02 TeV
Charged-particle spectra at midrapidity are measured in PbāPb collisions at the centre-of-mass energy per nucleonānucleon pair s NN =5.02 TeV and presented in centrality classes ranging from most central (0ā5%) to most peripheral (95ā100%) collisions. Possible medium effects are quantified using the nuclear modification factor (R AA ) by comparing the measured spectra with those from protonāproton collisions, scaled by the number of independent nucleonānucleon collisions obtained from a Glauber model. At large transverse momenta (
K*(892)(0) and phi(1020) production at midrapidity in pp collisions at root s=8 TeV
The production of K* (892)(0) and phi(1020) in pp collisions at root s = 8 TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The P-T-differential yields d(2)N/dydp(T), in the range 0 < p(T) < 20 GeV/c for K*(0) and 0.4 < p(T) < 16 GeV/c for phi have been measured at midrapidity, vertical bar y vertical bar < 0.5. Moreover, improved measurements of the K*(0)(892) and phi (1020) at root s = 7 TeV are presented. The collision energy dependence of p(T) distributions, p(T)-integrated yields, and particle ratios in inelastic pp collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In pp collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The P-T-differential yields of K*(0) and phi in pp collisions at root s = 8 TeV are compared with the expectations of different Monte Carlo event generators
Jet-associated deuteron production in pp collisions at ās=13 TeV
Deuteron production in high-energy collisions is sensitive to the spaceātime evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at s=13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (pT>5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4ā4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence
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