1,161 research outputs found
Measurements of with ALICE at the LHC
The ALICE detector provides excellent capabilities to study quarkonium
production at the Large Hadron Collider (LHC). Heavy quarkonia, bound states of
charm or beauty quark anti-quark pairs such as the , are
expected to be produced by initial hard processes. Thus they will provide
insight into the earliest and hottest stages of AA collisions where the
formation of a Quark-Gluon Plasma (QGP) is expected. Furthermore,
high-precision data from pp collisions represent an essential baseline for the
measurement of nuclear modifications in heavy-ions and serve also as a crucial
test for several models of quarkonium hadroproduction. In addition, the study
of pA collisions allows to investigate nuclear modifications due to Cold
Nuclear Matter (CNM) effects. In ALICE, were measured in pp
and Pb--Pb collisions down to = 0 via their di-electron decay
channel in the central barrel ( 0.8). Results on the nuclear
modification factor () at central rapidities in Pb--Pb
collisions at TeV will be shown and their
implications discussed. A separation of the prompt and non-prompt components is
also possible down to of the of 2 GeV/
Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at âsNN=5.02 TeV
Midrapidity production of ĎÂą, KÂą, and (ÂŻp)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at âsNN=5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0â90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/Ď) and kaon-to-pion (K/Ď) ratios, with similar measurements in Pb-Pb collisions at âsNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/Ď, K/Ď) as a function of pT show pronounced maxima at pTâ3 GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at âsNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at âsNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.publishedVersio
Spin alignment measurements using vector mesons with ALICE detector at the LHC
We present new measurements related to spin alignment of K*0 vector mesons at mid-rapidity for PbâPb collisions at âsNN = 2.76 and 5.02 TeV. The spin alignment measurements are carried out with respect to production plane and 2nd order event plane. At low pT the spin density matrix element Ď00 for K*0 is found to have values slightly below 1/3, while it is consistent with 1/3, i.e. no spin alignment, at high pT. Similar values of Ď00 are observed with respect to both production plane and event plane. Within statistical and systematic uncertainties, Ď00 values are also found to be independent of âsNN. Ď00 also shows centrality dependence with maximum deviation from 1/3 for mid-central collisions with respect to both the kinematic planes. The measurements for K*0 in pp collisions at âs = 13 TeV and for K0S (a spin 0 hadron) in 20-40% central PbâPb collisions at âsNN = 2.76 TeV are consistent with no spin alignment.publishedVersio
Study of J/Ď azimuthal anisotropy at forward rapidity in Pb-Pb collisions at âsNN=5.02 TeV
The second (v2) and third (v3) flow harmonic coefficients of J/Ď mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at â sNN = 5.02 TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, pT, for various collision centralities. A positive value of J/Ď v3 is observed with 3.7Ď significance. The measurements, compared to those of prompt D0 mesons and charged particles at mid-rapidity, indicate an ordering with vn(J/Ď) < vn(D0 ) < vn(hÂą) (n = 2, 3) at low and intermediate pT up to 6 GeV/c and a convergence with v2(J/Ď) â v2(D0 ) â v2(hÂą) at high pT above 6â8 GeV/c. In semicentral collisions (5â40% and 10â50% centrality intervals) at intermediate pT between 2 and 6 GeV/c, the ratio v3/v2 of J/Ď mesons is found to be significantly lower (4.6Ď) with respect to that of charged particles. In addition, the comparison to the prompt D0 -meson ratio in the same pT interval suggests an ordering similar to that of the v2 and v3 coefficients. The J/Ď v2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry.publishedVersio
Measurement of isolated photon-hadron correlations in âsNN = 5.02 TeV pp and p-Pb collisions
This paper presents isolated photon-hadron correlations using pp and p-Pb data collected by the ALICE detector at the LHC. For photons with |Ρ|<0.67 and 12<pT<40 GeV/c, the associated yield of charged particles in the range |Ρ|<0.80 and 0.5<pT<10 GeV/c is presented. These momenta are much lower than previous measurements at the LHC. No significant difference between pp and p-Pb is observed, with Pythia 8.2 describing both data sets within uncertainties. This measurement constrains nuclear effects on the parton fragmentation in p-Pb collisions, and provides a benchmark for future studies of Pb-Pb collisions.publishedVersio
Constraining the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Pb-Pb collisions at = 2.76 and 5.02 TeV
Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at = 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity (Ρ) and transverse momentum (pT) ranges |Ρ| < 0.8 and 0.2 < pT < 5 GeV/c. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators Îł1, 1â=âăcos(ĎÎąâ+âĎβâââ2Ψ2)ă and Îł1,âââ3â=âăcos(ĎÎąâââ3Ďβâ+â2Ψ2)ă. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured Îł1,1. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form Îł1, 2â=âăcos(ĎÎąâ+â2Ďβâââ3Ψ3)ă, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of Îł1,1.publishedVersio
Multiplicity dependence of light (anti-)nuclei production in pâPb collisions at âsNN=5.02 TeV
The measurement of the deuteron and anti-deuteron production in the rapidity range â1 < y < 0 as a function of transverse momentum and event multiplicity in pâPb collisions at âsNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-offlight. Their production in pâPb collisions is compared to pp and PbâPb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in PbâPb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in pâPb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window â1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.publishedVersio
J/Ď elliptic and triangular flow in Pb-Pb collisions at âsNN = 5.02 TeV
The inclusive J/Ď elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at sNNââââ = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 Îźbâ1 at forward rapidity and 93 Îźbâ1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/Ď v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/Ď v3 with a significance of more than 5Ď at forward rapidity in the pT range 2 < pT < 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT Ⲡ8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/Ď v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/Ď flow.publishedVersio
Mid-Staffordshire:a case study of failed governance and leadership?
Hadronic resonances are unique tools to investigate the interplay of re-scattering and regeneration effects during the hadronization phase in heavy-ion collisions. Measurements in small collision systems provide a necessary baseline for heavy-ion data, help to tune pQCD inspired event generators and give insight into the search for the onset of collective effects. As the Ď meson has a longer lifetime compared to other resonances, it is expected that its production would be much less affected by regeneration and re-scattering processes. We report on measurements of Ď meson production in minimum bias pp collisions at different beam energies and as a function of charged particle multiplicity with the ALICE detector at the LHC. The results include the transverse momentum (pT) distributions of Ď as well as the particle yield ratios. Finally, we have also studied the Ď effective strangeness content by comparing our results to theoretical calculations
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