9 research outputs found
Proposal of new observables for the study of reconstructed jets in heavy ion collisions
O Plasma de Quarks e Glúons (Qgp), um meio denso e quente, pode ser produzido em laboratório a partir da colisão entre íons pesados relativísticos. Pode-se estudá-lo a partir da comparação entre jatos reconstruídos em tais eventos e aqueles reconstruídos em colisões próton-próton, uma vez que se espera que os pártons ao atravessarem o Qgp percam energia em função da interação com o meio, o chamado jet quenching. Este trabalho propõe dois novos observáveis no estudo de jatos reconstruídos em colisões entre íons pesados relativísticos: o espectro de jatos quasi-inclusivo e a evolução do espectro de jatos de recuo em função da partícula trigger. Mostra-se que conhecida a função de resolução do momento reconstruído do jato é possível obter o espectro verdadeiro desses observáveis a partir da técnica de deconvolução bayesiana iterativa. A técnica proposta é empregada em eventos de colisões núcleonúcleo realizadas nos aceleradores Rhic e Lhc cujos dados foram coletados pelas colaborações Star e Alice, respectivamente. Os resultados evidenciam a ocorrência do fenômeno de jet queching independentemente do sistema, da energia e da centralidade da colisão em um grande intervalo cinemático.The Quark-Gluon Plasma (Qgp), a hot and dense medium, can be produced in laboratory by colliding relativistic heavy ion. This medium can be studied by the comparison of jets reconstructed in such events and those reconstructed in proton-proton collisions, once it is expected that partons lose energy when traversing the Qgp due to its interaction with the medium, the so-called jet quenching. This work proposes two new observables: the quasiinclusive jet spectrum and the evolution of the recoil jet spectrum as function of the trigger particle. It is shown that it is possible to obtain those spectra using iterative bayesian unfolding, which requires the resolution function for the reconstructed jet transverse momentum. This technique is applied to Star and Alice data which has been taken at Rhic and Lhc, respectively. The results indicate that jet quenching occurs in a very wide kinematic range, regardless the colliding system, its energy and centrality
production and nuclear effects in p-Pb collisions at = 5.02 TeV
Inclusive J/ production has been studied with the ALICE detector in p-Pb collisions at = 5.02 TeV at the CERN LHC, in the rapidity domains 2.03 < y < 3.53 and −4.46 < y < −2.96, down to zero transverse momentum. The J/ measurement is performed in the Muon Spectrometer through the decay mode. In this Letter, the J/ production cross section and the nuclear modification factor R for the rapidities under study are presented. While at forward rapidity a suppression of the J/ yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also shown differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.Inclusive J/ production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains and , down to zero transverse momentum, studying the decay mode. In this paper, the J/ production cross section and the nuclear modification factor for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/ yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results
Long-range angular correlations of π, K and p in p–Pb collisions at = 5.02 TeV
Angular 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 < < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range || < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, , is observed to be smaller than that for pions, , up to about = 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 is found to be smaller at low and larger at higher than , with a crossing occurring at about 2 GeV. 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.Angular 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 GeV/. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range . Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, , is observed to be smaller than that for pions, , up to about GeV/. 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 is found to be smaller at low and larger at higher than , with a crossing occurring at about 2 GeV. 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.Angular 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<pT<4 GeV/c . The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab|<0.8 . Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pT and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, v2p , is observed to be smaller than that for pions, v2π , up to about pT=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 v2p is found to be smaller at low pT and larger at higher pT than v2π , 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
Corrigendum to 'Multi-strange baryon production at mid-rapidity in Pb-Pb collisions at = 2.76 TeV' [Phys. Lett. B 728 (2014) 216-227]
Centrality, rapidity and transverse momentum dependence of suppression in Pb-Pb collisions at =2.76 TeV
The inclusive J/ nuclear modification factor () in Pb-Pb collisions at =2.76TeV has been measured by ALICE as a function of centrality in the decay channel at mid-rapidity |y| < 0.8 and as a function of centrality, transverse momentum and rapidity in the decay channel at forward-rapidity 2.5 < y < 4.The J/ yields measured in Pb-Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions.The integrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 +- 0.06 (stat.) +- 0.10 (syst.) at mid-rapidity and 0.57 +- 0.01 (stat.) +- 0.09 (syst.) at forward-rapidity. At low transverse momentum, significantly larger values of are measured at forward-rapidity compared to measurements at lower energy.These features suggest that a contribution to the J/ yield originates from charm quarks (re)combination in the deconfined partonic medium.The inclusive J/ψ nuclear modification factor ( RAA ) in Pb–Pb collisions at sNN=2.76 TeV has been measured by ALICE as a function of centrality in the e+e− decay channel at mid-rapidity ( |y|<0.8 ) and as a function of centrality, transverse momentum and rapidity in the μ+μ− decay channel at forward-rapidity ( 2.5<y<4 ). The J/ψ yields measured in Pb–Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAA integrated over a centrality range corresponding to 90% of the inelastic Pb–Pb cross section is 0.72±0.06(stat.)±0.10(syst.) at mid-rapidity and 0.58±0.01(stat.)±0.09(syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAA are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/ψ yield originates from charm quark (re)combination in the deconfined partonic medium.The inclusive nuclear modification factor in Pb-Pb collisions at =2.76 TeV has been measured by ALICE as a function of centrality in the ee decay channel at mid-rapidity and as a function of centrality, transverse momentum and rapidity in the decay channel at forward-rapidity .The yields measured in Pb-Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The integrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is (stat.) (syst.) at mid-rapidity and (stat.) (syst.) at forward-rapidity. At low transverse momentum, significantly larger values of are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the yield originates from charm quarks (re)combination in the deconfined partonic medium
Two- and three-pion quantum statistics correlations in Pb-Pb collisions at 2.76 TeV at the CERN Large Hadron Collider
Correlations induced by quantum statistics are sensitive to the spatio-temporal extent as well as dynamics of particle emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two and three-pion correlations of same and mixed-charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at = 2.76 TeV at the LHC with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission.The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged pion emission of 22% +- 12%.Correlations induced by quantum statistics are sensitive to the spatio-temporal extent as well as dynamics of particle emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two and three-pion correlations of same and mixed-charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at TeV at the LHC with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged pion emission of 23% 8%.Correlations induced by quantum statistics are sensitive to the spatiotemporal extent as well as dynamics of particle-emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two- and three-pion correlations of same and mixed charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at sNN=2.76 TeV at the CERN Large Hadron Collider with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged-pion emission of 23%±8%.</p
Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=7 TeV
The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has
been measured at midrapidity (jyj < 0:5) in proton-proton collisions at ffisffiffi
p
¼ 7 TeV with ALICE at the
LHC. Electrons were measured in the transverse momentum range 0:5<pt < 8 GeV=c. Predictions from
a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data
within the theoretical and experimental uncertainties