1,083 research outputs found
Transverse momentum dependence of inclusive primary charged-particle production in p-Pb collisions at root S-NN=5.02 TeV
No full textThe transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC in the range 0.15 < pT < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at root S-NN = 2.76 TeV
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
Λ+c production in pp collisions at √s = 7 TeV and in p-Pb collisions at √sNN = 5.02 TeV
No full textThe pT-differential production cross section of prompt Λ+c charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at √s = 7 TeV and in p-Pb collisions at √sNN = 5.02 TeV at midrapidity. The Λ+c and Λ–c were reconstructed in the hadronic decay modes Λ+c → pK−π+, Λ+c → pK0S and in the semileptonic channel Λ+c → e+νeΛ (and charge conjugates). The measured values of the Λ+c /D0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and pT intervals, where the Λ+c production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ+c nuclear modification factor, RpPb, is also presented. The RpPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium
Long-range angular correlations of π, K and p in p–Pb collisions at
No full textAngular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3 < p(T) < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar n(lab)vertical bar < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of p(T) and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, 4, is observed to be smaller than that for pions, v(2)(pi), up to about p(T) = 2 GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v(2)(p) is found to be smaller at low P-T and larger at higher p(T) than v(2)(pi), with a crossing occurring at about 2 GeV/c. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved
Neutral pion and eta meson production in p-Pb collisions at root S-NN=5.02 TeV
No full textCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULONeutral pion and eta meson invariant differential yields were measured in non-single diffractive p-Pb collisions at root S-NN = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of pi(0) and eta meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of 0.3 < p(T) < 20 GeV/c and 0.7 < p(T) < 20 GeV/c, respectively. The measured eta/pi(0) ratio increases with p(T) and saturates for p(T) gt; 4 GeV/c at 0.483 +/- 0.015(stat) +/- 0.015(sys). A deviation from m(T) scaling is observed for p(T) < 2 GeV/c. The measured eta/pi(0) ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full pi range. The measured eta/pi(0) ratio at high p(T) also agrees within uncertainties with measurements from nucleus nucleus collisions. The pi(0) and eta yields in p-Pb relative to the scaled pp interpolated reference, R-pPb, are presented for 0.3 < p(T) < 20 GeV/c and 0.7 < p(T) < 20 GeV/c, respectively. The results are compared with theoretical model calculations. The values of R-pPb are consistent with unity for transverse momenta above 2 GeV/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb-Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.788125CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig
p-p, p-Lambda, and Lambda-Lambda correlations studied via femtoscopy in pp reactions at root s=7 TeV
No full textWe report on the first femtoscopic measurement of baryon pairs, such as p-p, p-Λ, and Λ-Λ, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at s=7TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-Λ, and Λ-Λ correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems: Correlation Analysis Tool using the Schrödinger equation (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to r0=1.125±0.018(stat)-0.035+0.058(syst) fm. The sensitivity of the measured p-Λ correlation is tested against different scattering parameters, which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the Λ-Λ correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models
Neutral pion and η meson production in p–Pb collisions at √sNN = 5.02 TeV
No full textNeutral pion and η meson invariant differential yields were measured in non-single diffractive p–Pb colli- sions at √sNN = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of π0 and η meson inclu- sive production are measured near mid-rapidity in a broad transverse momentum range of 0.3 4 GeV/c at 0.483 ± 0.015stat ± 0.015sys . A deviation from m T scaling is observed for pT < 2 GeV/c. The measured η/π0 ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full pT range. The measured η/π0 ratio at high pT also agrees within uncertainties with measure- ments from nucleus–nucleus collisions. The π 0 and η yields in p–Pb relative to the scaled pp interpolated reference, RpPb, arepresentedfor0.3< pT <20GeV/cand0.7< pT <20 GeV/c, respectively. The results are compared with theoreti- cal model calculations. The values of RpPb are consistent with unity for transverse momenta above 2 GeV/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium
Transverse momentum dependence of inclusive primary charged-particle production in p–Pb collisions at √sNN=5.02 TeV
No full textThe transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC in the range 0.15 < pT < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at root S-NN = 2.76 TeV
K*(892)(0) and phi(1020)meson production at high transverse momentum in pp and Pb-Pb collisions at root sNN=2.76 TeV
No full textThe production of K*(892)(0) and phi(1020) mesons in proton-proton
(pp) and lead-lead (Pb-Pb) collisions at root sNN = 2.76 TeV has been
analyzed using a high luminosity data sample accumulated in 2011 with
the ALICE detector at the Large Hadron Collider (LHC). Transverse
momentum (p(T)) spectra have been measured for K*(892)(0) and
phi(1020) mesons via their hadronic decay channels for p(T) up to 20
GeV/c. The measurements in pp collisions have been compared to model
calculations and used to determine the nuclear modification factor and
particle ratios. The K*(892)(0)/K ratio exhibits significant reduction
from pp to central Pb-Pb collisions, consistent with the suppression of
the K*( 892)(0) yield at low pT due to rescattering of its decay
products in the hadronic phase. In central Pb-Pb collisions the pT
dependent phi(1020)/p and K*(892)0/p ratios show an enhancement over
pp collisions for pT approximate to 3 GeV/c, consistent with previous
observations of strong radial flow. At high pT, particle ratios in Pb-Pb
collisions are similar to those measured in pp collisions. In central
Pb-Pb collisions, the production of K*(892)(0) and phi(1020) mesons is
suppressed for p(T) > 8 GeV/c. This suppression is similar to that of
charged pions, kaons, and protons, indicating that the suppression does
not depend on particle mass or flavor in the light quark sector
Production of K∗ (892) 0 and ϕ(1020) in p–Pb collisions at √sNN = 5.02 TeV
No full textThe production of K∗(892)0 and ϕ(1020) mesons has been measured in p–Pb collisions at √sNN = 5.02 TeV. K∗0 and ϕ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range −0.5<y<0. The transverse momentum spectra, measured as a function of the multiplicity, have a pT range from 0 to 15 GeV/c for K∗0 and from 0.3 to 21 GeV/c for ϕ. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at s√ = 7 TeV and Pb–Pb collisions at √sNN = 2.76 TeV. In Pb–Pb and p–Pb collisions, K∗0 and ϕ probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by comparison with other identified hadrons. For this purpose, the mean transverse momenta and the differential proton-to-ϕ ratio are discussed as a function of the multiplicity of the event. The short-lived K∗0 is measured to investigate re-scattering effects, believed to be related to the size of the system and to the lifetime of the hadronic phase.peerReviewe
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