The transverse momentum (p T) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at √ s NN = 5.02 TeV with the ALICE detector at the LHC in the range ...0.15 < p T < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp colli-sions, leading to a nuclear modification factor consistent with unity for p T larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for p T around 4 GeV/c. The mea-surement is compared to theoretical calculations and to data in Pb–Pb collisions at √ s NN = 2.76 TeV. Measurements of particle production in proton-nucleus colli-sions at high energies enable the study of fundamental proper-ties of Quantum Chromodynamics (QCD) over a broad range of parton fractional momentum x and parton densities (see 1 for a review). They also provide reference measurements for the studies of deconfined matter created in nucleus–nucleus collisions 2. The first measurements of charged-particle production in minimum-bias p–Pb collisions at the LHC at a centre-of-mass energy per nucleon-nucleon pair of √ s NN = 5.02 TeV
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Invariant yields of neutral pions at midrapidity in the transverse momentum range 0.6 < p T < 12 GeV/c mea-sured in Pb–Pb collisions at √ s NN = 2.76 TeV are presented for six centrality classes. The ...pp reference spectrum was mea-sured in the range 0.4 < p T < 10 GeV/c at the same center-of-mass energy. The nuclear modification factor, R AA , shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about 8−10 for 5 p T 7 GeV/c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the first measurement of the net-charge fluctuations in Pb-Pb collisions at \surd s_NN 2.76 TeV, measured with the ALICE detector at the CERN Large Hadron Collider. The dynamical ...fluctuations per unit entropy are observed to decrease when going from peripheral to central collisions. An additional reduction in the amount of fluctuations is seen in comparison to the results from lower energies. We examine the dependence of fluctuations on the pseudo-rapidity interval, which may account for the dilution of fluctuations during the evolution of the system. We find that the ALICE data points are between the theoretically predicted values for a hadron gas and a Quark-Gluon Plasma.
Azimuthally anisotropic distributions of D0, D+ and D*+ mesons were studied in the central rapidity region (|y|<0.8) in Pb-Pb collisions at a centre-of-mass energy sqrts(s_NN) = 2.76TeV per ...nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient v2 (commonly denoted elliptic flow) was measured in the centrality class 30-50% as a function of the D meson transverse momentum pt, in the range 2-16GeV/c$. The measured v2 of D mesons is comparable in magnitude to that of light-flavour hadrons. It is positive in the range 2 < pt < 6 GeV/c with 5.7 sigma significance, based on the combination of statistical and systematic uncertainties.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE ...experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs.
The yield of charged particles associated with high-pT trigger particles (8 < pT < 15 GeV/c) is measured with the ALICE detector in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV relative to proton-proton ...collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jet-like correlation peaks in azimuthal di-hadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta pT > 3 GeV/c on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found.
Identical neutral kaon pair correlations are measured in sqrt{s}=7 TeV pp collisions in the ALICE experiment. One-dimensional K0s-K0s correlation functions in terms of the invariant momentum ...difference of kaon pairs are formed in two multiplicity and two transverse momentum ranges. The femtoscopic parameters for the radius and correlation strength of the kaon source are extracted. The fit includes quantum statistics and final-state interactions of the a0/f0 resonance. K0s-K0s correlations show an increase in radius for increasing multiplicity and a slight decrease in radius for increasing transverse mass, mT, as seen in pion-pion correlations in the pp system and in heavy-ion collisions. Transverse mass scaling is observed between the K0s-K0s and pion-pion radii. Also, the first observation is made of the decay of the f2'(1525) meson into the K0s-K0s channel in pp collisions.
A measurement of the multi-strange Xi- and Omega- baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for proton-proton collisions at centre ...of mass energy of 7 TeV. The transverse momentum (pt) distributions were studied at mid-rapidity (|y| < 0.5) in the range of 0.6 < pt < 8.5 GeV/c for Xi- and Xi+ baryons, and in the range of 0.8 < pt < 5 GeV/c for Omega- and Omega+. Baryons and anti-baryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current LHC data has allowed us to measure a difference between the mean pt of Xi- (Xi+) and Omega- (Omega+). Particle yields, mean pt, and the spectra in the intermediate pt range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Omega- (Omega+). This PYTHIA tune approaches the pt spectra of Xi- and Xi+ baryons below pt < 0.85 GeV/c and describes the Xi- and Xi+ spectra above pt > 6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of (Omega-+Omega+)/(Xi-+Xi+) as a function of transverse mass.
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