Production of identified and unidentified charged hadrons in Pb--Pb collisions at \sqrt{s_{\rm NN}}~5.02~TeV

In late 2015, the ALICE collaboration recorded data from Pb--Pb collisions at the unprecedented energy of \sqrt{s_{\rm NN}}~5.02~TeV. The transverse-momentum ($p_{\rm T}$) spectra of pions, kaons and protons are presented. The evolution of the particle ratios as a function of collision energy and centrality is discussed. The ratio between $p_{\rm T}$-integrated particle yields are measured and compared to different collision energies as well as smaller collision systems. For the study of energy loss mechanisms in the QCD medium at high transverse momenta, the nuclear modification factors ($R_{AA}$) are computed and compared with results obtained at lower energy

PID performance of the ALICE-TOF detector in Run 2

In these proceedings we report on the status of the ALICE Time-Of-Flight (TOF) detector. The running performance of the Run 1 (2009-2013) and Run 2 (2015-present) data taking campaigns are compared. The Particle IDentification (PID) capabilities of the detector are presented and discussed in the light of the improved detector calibration that allowed to reach a timing resolution of 56 ps

Measuring hydrodynamical expansion via the production of identified hadrons in Pb-Pb collisions with ALICE

During the LHC Run-2, ALICE has collected data from Pb–Pb collisions at √ sNN =5.02 TeV. The centrality dependence of identified particle production, includingelliptic (v2) and higher harmonic flow coefficients (v3, v4), has been measured.The high-precision measurement of transverse momentum (pT) differential ellipticflow of the φ-meson (whose mass is close to that of the proton) allows for aunique testing of mass ordering at low pT as well as baryon and meson groupingat intermediate pT. The pT-differential hadron spectra are presented and,together with flow coefficients, compared with state-of-the-art calculationsfrom models based on relativistic hydrodynamics coupled with UrQMD. The addedtransport code is to describe rescattering in the hadronic phase, which has beensuccessful in describing the pT-spectra of identified particles up to a fewGeV/c. Moreover, results from the simultaneous Blast-Wave fit to the pTdistributions are compared across multiple collisions energies and system sizesin order to address the evolution of collective behaviour from small systems tolarge systems.During the LHC Run-2, ALICE has collected data from Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. The centrality dependence of identified particle production, including elliptic ($v_{2}$) and higher harmonic flow coefficients ($v_{3},v_{4}$), has been measured. The high-precision measurement of transverse momentum ($p_{\rm T}$) differential elliptic flow of the $\phi$-meson (whose mass is close to that of the proton) allows for a unique testing of mass ordering at low $p_{\rm T}$ as well as baryon and meson grouping at intermediate $p_{\rm T}$. The $p_{\rm T}$-differential hadron spectra are presented and, together with flow coefficients, compared with state-of-the-art calculations from models based on relativistic hydrodynamics coupled with UrQMD. The added transport code is to describe rescattering in the hadronic phase, which has been successful in describing the $p_{\rm T}$-spectra of identified particles up to a few GeV/$c$. Moreover, results from the simultaneous Blast-Wave fit to the $p_{\rm T}$ distributions are compared across multiple collisions energies and system sizes in order to address the evolution of collective behaviour from small systems to large systems

Studying light flavour hadrons produced in the collision of different nuclei at the LHC

The study of identified particle production as a function of event multiplicity is a key tool for understanding the similarities and differences among different colliding systems. Now for the first time, we can investigate how particle production is affected by the collision geometry in heavy-ion collisions at the LHC. In these proceedings, we report newly obtained ALICE results on charged and identified particle production in Pb–Pb and Xe–Xe collision at $\sqrt {{S_{NN}}} = 5.02$ and $\sqrt {{S_{NN}}} = 5.44$ TeV, respectively, as a function of transverse momentum (pT) and collision centrality. Particle spectra and ratios are compared between two different colliding systems at similar charged-particle multiplicity densities (〈dNch/dη〉), and different initial eccentricities. We find that in central collisions, spectral shapes of different particles are driven by their masses. The pT-integrated particle yield ratios follow the same trends with 〈dNch=dη〉 as previously observed in other systems, further suggesting that at the LHC energies, event hadrochemistry is dominantly driven by the charged-particle multiplicity density and not the collision system, geometry or center-of-mass energy

PID performance of the ALICE-TOF detector in Run 2

In these proceedings we report on the status of the ALICE Time-Of-Flight (TOF) detector. The running performance of the Run 1 (2009-2013) and Run 2 (2015-present) data taking campaigns are compared. The Particle IDentification (PID) capabilities of the detector are presented and discussed in the light of the improved detector calibration that allowed to reach a timing resolution of 56 ps.In these proceedings we report on the status of the ALICE Time-Of-Flight (TOF) detector.The running performance of the Run 1 (2009-2013) and Run 2 (2015-present) data taking campaigns are compared.The particle identification capabilities of the detector are presented and discussed in the light of the improved detector calibration that allowed to reach a timing resolution of 56 ps

Forward rapidity J/ψ production as a function of charged-particle multiplicity in pp collisions at s \sqrt{s} = 5.02 and 13 TeV

International audienceThe production of J/ψ is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies $\sqrt{s}$ = 5.02 and 13 TeV. The J/ψ mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5 < y < 4.0), whereas the charged-particle multiplicity density (dN$_{ch}$/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$_{ch}$/dη/〈dN$_{ch}$/dη〉), 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 (〈p$_{T}$〉) of J/ψ in pp collisions exhibits an increasing trend as a function of dN$_{ch}$/dη/〈dN$_{ch}$/dη〉 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 s√=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