7 research outputs found
Mesure de la production de J/Ï lors de collisions Pb-Pb Ă âs=5.02 TeV avec le spectromĂštre Ă muons de l'expĂ©rience ALICE-CERN
Ultra-relativistic heavy ion collisions aim at creating and studying, in the laboratory, the hadronic matter at high temperature and energy density.According to the QCD, a deconfined state of partonic matter, the Quark-Gluon Plasma (QGP), should be created at temperatures exceeding 200 MeV (about a trillion degrees).The production of charmonium states (J/Ï et Ï(2S)) is one of the various probes studied to access to the QGP properties. In the presence of a strongly interacting medium, its production rate is affected by different mechanisms varying with the energy of the collision. A suppression associated to the color screening of the quark-antiquark pair was already observed by many experiments at the SPS and RHIC. However, this suppression was found to be less significant at low transverse momentum for LHC energies that can be explained by the recombination mechanism of charms anti-charms pairs during the QGP expansion.Also, the ALICE Collaboration reported in 2015 the first measurement of an excess in the yield of J/Ï at very low transverse momentum in Pb-Pb collisions at âsNN=2.76 TeV. The coherent photoproduction was proposed as the potential, although unexpected, underlying mechanism in collisions dominated by hadronic interactions. In this thesis, the inclusive J/Ï production was measured in Pb-Pb collisions at âsNN=5.02 TeV with the muon spectrometer of the ALICE experiment. The measurement of its nuclear modification factor (RAA) has been extended to the full data set corresponding to an integrated luminosity of 750 ÎŒb-1 and allowing for a better accuracy in centrality. Finally, the coherent photoproduction cross section has been exctrated from a yield with a significance greater than 5Ï in the 30-50%, 50-70% and 70-90% centrality ranges.Les collisions dâions lourds ultra-relativistes sont un outil unique pour crĂ©er et Ă©tudier en laboratoire la matiĂšre hadronique Ă hautes tempĂ©ratures et hautes densitĂ©s dâĂ©nergie. DâaprĂšs la QCD, un Ă©tat dĂ©confinĂ© de la matiĂšre hadronique, le Plasma de Quarks et de Gluons (QGP), devrait ĂȘtre crĂ©Ă© Ă des tempĂ©ratures excĂ©dant les 200 MeV (de l'ordre du billion des degrĂ©s). La production des Ă©tats de charmonia (J/Ï et Ï(2S)) est lâune des multiples sondes Ă©tudiĂ©es pour accĂ©der aux propriĂ©tĂ©s du QGP. En prĂ©sence dâun milieu dense interagissant fortement, son taux de production est affectĂ© par diffĂ©rents mĂ©canismes variant avec lâĂ©nergie de la collision. Une suppression associĂ©e Ă lâĂ©crantage de couleur de la paire de quarks-antiquarks fut dĂ©jĂ observĂ©e par de nombreuses expĂ©riences au SPS et au RHIC. Cette suppression sâest nĂ©anmoins avĂ©rĂ©e moins significative Ă basse impulsion transverse pour les Ă©nergies du LHC cela sâexpliquant par lâaction dâun mĂ©canisme de recombinaison des charmes anti-charmes durant lâexpansion du QGP. De plus, la collaboration ALICE a reportĂ© en 2015 une premiĂšre mesure dâun excĂšs de J/Ï rĂ©sidant Ă trĂšs basse impulsion transverse lors de collisions Pb-Pb Ă âsNN=2.76 TeV. La photoproduction cohĂ©rente fut proposĂ©e comme mĂ©canisme sous-jacent, bien quâinattendu lors de collisions dominĂ©es par les interactions hadroniques. Dans cette thĂšse, la production inclusive de J/Ï fut mesurĂ©e avec les collisions Pb-Pb Ă âsNN=5.02 TeV Ă lâaide du spectromĂštre Ă muons de lâexpĂ©rience ALICE. La mesure de son facteur de modification nuclĂ©aire (RAA) a Ă©tĂ© Ă©tendue Ă lâensemble des donnĂ©es correspondante Ă une luminositĂ© intĂ©grĂ©e de 750 ÎŒb-1 et permettant une meilleure prĂ©cision en centralitĂ©. Enfin, la section efficace de photoproduction cohĂ©rente a Ă©tĂ© extraite Ă partir d'un taux significativement supĂ©rieur Ă 5Ï dans les collisions d'une centralitĂ© de 30-50%, 50-70% et 70-90%
Mesure de la production de J/Ï lors de collisions Pb-Pb Ă âs=5.02 TeV avec le spectromĂštre Ă muons de l'expĂ©rience ALICE-CERN
Ultra-relativistic heavy ion collisions aim at creating and studying, in the laboratory, the hadronic matter at high temperature and energy density.According to the QCD, a deconfined state of partonic matter, the Quark-Gluon Plasma (QGP), should be created at temperatures exceeding 200 MeV (about a trillion degrees).The production of charmonium states (J/Ï et Ï(2S)) is one of the various probes studied to access to the QGP properties. In the presence of a strongly interacting medium, its production rate is affected by different mechanisms varying with the energy of the collision. A suppression associated to the color screening of the quark-antiquark pair was already observed by many experiments at the SPS and RHIC. However, this suppression was found to be less significant at low transverse momentum for LHC energies that can be explained by the recombination mechanism of charms anti-charms pairs during the QGP expansion.Also, the ALICE Collaboration reported in 2015 the first measurement of an excess in the yield of J/Ï at very low transverse momentum in Pb-Pb collisions at âsNN=2.76 TeV. The coherent photoproduction was proposed as the potential, although unexpected, underlying mechanism in collisions dominated by hadronic interactions. In this thesis, the inclusive J/Ï production was measured in Pb-Pb collisions at âsNN=5.02 TeV with the muon spectrometer of the ALICE experiment. The measurement of its nuclear modification factor (RAA) has been extended to the full data set corresponding to an integrated luminosity of 750 ÎŒb-1 and allowing for a better accuracy in centrality. Finally, the coherent photoproduction cross section has been exctrated from a yield with a significance greater than 5Ï in the 30-50%, 50-70% and 70-90% centrality ranges.Les collisions dâions lourds ultra-relativistes sont un outil unique pour crĂ©er et Ă©tudier en laboratoire la matiĂšre hadronique Ă hautes tempĂ©ratures et hautes densitĂ©s dâĂ©nergie. DâaprĂšs la QCD, un Ă©tat dĂ©confinĂ© de la matiĂšre hadronique, le Plasma de Quarks et de Gluons (QGP), devrait ĂȘtre crĂ©Ă© Ă des tempĂ©ratures excĂ©dant les 200 MeV (de l'ordre du billion des degrĂ©s). La production des Ă©tats de charmonia (J/Ï et Ï(2S)) est lâune des multiples sondes Ă©tudiĂ©es pour accĂ©der aux propriĂ©tĂ©s du QGP. En prĂ©sence dâun milieu dense interagissant fortement, son taux de production est affectĂ© par diffĂ©rents mĂ©canismes variant avec lâĂ©nergie de la collision. Une suppression associĂ©e Ă lâĂ©crantage de couleur de la paire de quarks-antiquarks fut dĂ©jĂ observĂ©e par de nombreuses expĂ©riences au SPS et au RHIC. Cette suppression sâest nĂ©anmoins avĂ©rĂ©e moins significative Ă basse impulsion transverse pour les Ă©nergies du LHC cela sâexpliquant par lâaction dâun mĂ©canisme de recombinaison des charmes anti-charmes durant lâexpansion du QGP. De plus, la collaboration ALICE a reportĂ© en 2015 une premiĂšre mesure dâun excĂšs de J/Ï rĂ©sidant Ă trĂšs basse impulsion transverse lors de collisions Pb-Pb Ă âsNN=2.76 TeV. La photoproduction cohĂ©rente fut proposĂ©e comme mĂ©canisme sous-jacent, bien quâinattendu lors de collisions dominĂ©es par les interactions hadroniques. Dans cette thĂšse, la production inclusive de J/Ï fut mesurĂ©e avec les collisions Pb-Pb Ă âsNN=5.02 TeV Ă lâaide du spectromĂštre Ă muons de lâexpĂ©rience ALICE. La mesure de son facteur de modification nuclĂ©aire (RAA) a Ă©tĂ© Ă©tendue Ă lâensemble des donnĂ©es correspondante Ă une luminositĂ© intĂ©grĂ©e de 750 ÎŒb-1 et permettant une meilleure prĂ©cision en centralitĂ©. Enfin, la section efficace de photoproduction cohĂ©rente a Ă©tĂ© extraite Ă partir d'un taux significativement supĂ©rieur Ă 5Ï dans les collisions d'une centralitĂ© de 30-50%, 50-70% et 70-90%
Mesure de la production de J/Ï lors de collisions Pb-Pb Ă âs=5.02 TeV avec le spectromĂštre Ă muons de l'expĂ©rience ALICE-CERN
Ultra-relativistic heavy ion collisions aim at creating and studying, in the laboratory, the hadronic matter at high temperature and energy density.According to the QCD, a deconfined state of partonic matter, the Quark-Gluon Plasma (QGP), should be created at temperatures exceeding 200 MeV (about a trillion degrees).The production of charmonium states (J/Ï et Ï(2S)) is one of the various probes studied to access to the QGP properties. In the presence of a strongly interacting medium, its production rate is affected by different mechanisms varying with the energy of the collision. A suppression associated to the color screening of the quark-antiquark pair was already observed by many experiments at the SPS and RHIC. However, this suppression was found to be less significant at low transverse momentum for LHC energies that can be explained by the recombination mechanism of charms anti-charms pairs during the QGP expansion.Also, the ALICE Collaboration reported in 2015 the first measurement of an excess in the yield of J/Ï at very low transverse momentum in Pb-Pb collisions at âsNN=2.76 TeV. The coherent photoproduction was proposed as the potential, although unexpected, underlying mechanism in collisions dominated by hadronic interactions. In this thesis, the inclusive J/Ï production was measured in Pb-Pb collisions at âsNN=5.02 TeV with the muon spectrometer of the ALICE experiment. The measurement of its nuclear modification factor (RAA) has been extended to the full data set corresponding to an integrated luminosity of 750 ÎŒb-1 and allowing for a better accuracy in centrality. Finally, the coherent photoproduction cross section has been exctrated from a yield with a significance greater than 5Ï in the 30-50%, 50-70% and 70-90% centrality ranges.Les collisions dâions lourds ultra-relativistes sont un outil unique pour crĂ©er et Ă©tudier en laboratoire la matiĂšre hadronique Ă hautes tempĂ©ratures et hautes densitĂ©s dâĂ©nergie. DâaprĂšs la QCD, un Ă©tat dĂ©confinĂ© de la matiĂšre hadronique, le Plasma de Quarks et de Gluons (QGP), devrait ĂȘtre crĂ©Ă© Ă des tempĂ©ratures excĂ©dant les 200 MeV (de l'ordre du billion des degrĂ©s). La production des Ă©tats de charmonia (J/Ï et Ï(2S)) est lâune des multiples sondes Ă©tudiĂ©es pour accĂ©der aux propriĂ©tĂ©s du QGP. En prĂ©sence dâun milieu dense interagissant fortement, son taux de production est affectĂ© par diffĂ©rents mĂ©canismes variant avec lâĂ©nergie de la collision. Une suppression associĂ©e Ă lâĂ©crantage de couleur de la paire de quarks-antiquarks fut dĂ©jĂ observĂ©e par de nombreuses expĂ©riences au SPS et au RHIC. Cette suppression sâest nĂ©anmoins avĂ©rĂ©e moins significative Ă basse impulsion transverse pour les Ă©nergies du LHC cela sâexpliquant par lâaction dâun mĂ©canisme de recombinaison des charmes anti-charmes durant lâexpansion du QGP. De plus, la collaboration ALICE a reportĂ© en 2015 une premiĂšre mesure dâun excĂšs de J/Ï rĂ©sidant Ă trĂšs basse impulsion transverse lors de collisions Pb-Pb Ă âsNN=2.76 TeV. La photoproduction cohĂ©rente fut proposĂ©e comme mĂ©canisme sous-jacent, bien quâinattendu lors de collisions dominĂ©es par les interactions hadroniques. Dans cette thĂšse, la production inclusive de J/Ï fut mesurĂ©e avec les collisions Pb-Pb Ă âsNN=5.02 TeV Ă lâaide du spectromĂštre Ă muons de lâexpĂ©rience ALICE. La mesure de son facteur de modification nuclĂ©aire (RAA) a Ă©tĂ© Ă©tendue Ă lâensemble des donnĂ©es correspondante Ă une luminositĂ© intĂ©grĂ©e de 750 ÎŒb-1 et permettant une meilleure prĂ©cision en centralitĂ©. Enfin, la section efficace de photoproduction cohĂ©rente a Ă©tĂ© extraite Ă partir d'un taux significativement supĂ©rieur Ă 5Ï dans les collisions d'une centralitĂ© de 30-50%, 50-70% et 70-90%
Forward rapidity J/Ï production as a function of charged-particle multiplicity in pp collisions at = 5.02 and 13 TeV
International audienceThe production of J/Ï is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies = 5.02 and 13 TeV. The J/Ï mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 < y < 4.0), whereas the charged-particle multiplicity density (dN/dη) is measured at midrapidity (|η| < 1). The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (dN/dη/â©dN/dηâȘ), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum (â©pâȘ) of J/Ï in pp collisions exhibits an increasing trend as a function of dN/dη/â©dN/dηâȘ showing a saturation towards high charged-particle multiplicities.[graphic not available: see fulltext
Enhanced deuteron coalescence probability in jets
The transverse-momentum (pT) spectra and coalescence parameters B2 of (anti)deuterons are measured in pp collisions at sâ=13 TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest pT in the event (pleadT>5 GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions and the jet signal is obtained as the difference between the Toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the Transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons inside the jet cone as compared to the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase space distributions of nucleons are generated using PYTHIA 8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in PYTHIA 8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the BJet2 is not reproduced by the models, which instead give a decreasing trend
Measurements of azimuthal anisotropies at forward and backward rapidity with muons in high-multiplicity pâPb collisions at âsNN = 8.16 TeV
The study of the azimuthal anisotropy of inclusive muons produced in p-Pb collisions at sNNââââ=8.16 TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, v2, is performed as a function of transverse momentum pT in the 0-20% high-multiplicity interval at both forward (2.032 GeV/c. The v2 coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward-central two-particle correlations. Both techniques give compatible results. A positive v2 is measured at both forward and backward rapidities with a significance larger than 4.7Ï and 7.6Ï, respectively, in the interval 2<pT<6 GeV/c. Comparisons with previous measurements in p-Pb collisions at sNNââââ=5.02 TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems
Hypertriton production in pâPb collisions at âsNN = 5.02 TeV
The study of nuclei and antinuclei production has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. The first measurement of the production of 3ÎH in p-Pb collisions at sNNââââ = 5.02 TeV is presented in this Letter. Its production yield measured in the rapidity interval â1<y<0 for the 40% highest multiplicity p-Pb collisions is dN/dy=[6.3±1.8(stat.)±1.2(syst.)]Ă10â7. The measurement is compared with the expectations of statistical hadronisation and coalescence models, which describe the nucleosynthesis in hadronic collisions. These two models predict very different yields of the hypertriton in charged particle multiplicity environments relevant to small collision systems such as p-Pb and therefore the measurement of dN/dy is crucial to distinguish between them. The precision of this measurement leads to the exclusion with a significance larger than 6.9Ï of some configurations of the statistical hadronization model, thus constraining the theory behind the production of loosely bound states at hadron colliders