Production and nuclear modification factors of pions, kaons and protons in pp and AA collisions at the LHC

In heavy-ion collisions at relativistic energies, a deconfined strongly-interacting state of matter is created. The elementary degrees of freedom of this state are the ones of Quantum Chromodynamics (QCD), namely quarks and gluons, hence its name Quark-Gluon Plasma (QGP). At the CERN Large Hadron Collider (LHC), protons and heavy-ions are accelerated at the highest energies ever achieved in the laboratory. The detector of A Large Ion Collider Experiment (ALICE) at the LHC, was especially designed to study the physics of the QGP produced in heavy-ion collisions. The “bulk” of the produced particles is constituted by hadrons containing only the “light” flavor quarks (u, d, s). Most of these hadrons are produced at low transverse momentum (pT) and originate from soft QCD processes. In this work, the production of π±, K±, p and p̄ has been measured in Pb–Pb collisions at √sNN = 5.02 TeV and in inelastic pp collisions at √s = 5.02 TeV. To this end, the excellent PID performance of the ALICE Time-Of-Flight detector (TOF) were exploited. The pT spectra of pions, kaons and protons have been measured in a wide momentum range (from 100 MeV/c to 12 GeV/c) and as a function of centrality. Based on this measurements, it was possible to characterize the medium formed in the collision. Particle production at low pT exhibits features typical of the collective evolution of a strongly interacting medium. At this energy the largest radial flow velocity is observed. The thermal properties of the medium can be accessed by studying the relative particle abundances in the framework of Statistical Hadronization Models. The Nuclear Modification Factor was computed to quantify the effect of parton energy loss in the QGP on high-pT particle production. The results are interpreted in comparison to predictions from state-of-the-art models and to similar measurements at the LHC

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

CERNBox User Forum

Scientific collaboration plays an ever-increasing role in our world. The need for tools that make it easy to share results, portable setups, and code is fundamental. The use of CERNbox and Jupyter notebooks with SWAN has become de facto the standard to ensure collaboration across many people and to handle several projects. In this talk, I will report on my experience as an ALICE user, and I will be giving my feedback and a few suggestions

Production and nuclear modification factors of pions, kaons and protons in pp and AA collisions at the LHC

In heavy-ion collisions at relativistic energies, a deconfined strongly-interacting state of matter is created. The elementary degrees of freedom of this state are the ones of Quantum Chromo Dynamics (QCD), namely quarks and gluons, hence its name Quark Gluon Plasma (QGP). At the CERN Large Hadron Collider (LHC), protons and heavy-ions are accelerated at the highest energies ever achieved in the laboratory. The detector of A Large Ion Collider Experiment (ALICE) at the LHC, was specially designed to study the physics of the QGP produced in heavy-ion collisions. The extensive Particle Identification (PID) capabilities of the ALICE detector allow for the study of a wide set of observables related to particle production mechanisms and sensitive to the properties and the evolution of the QGP. The ``bulk'' of the produced particles is constituted by hadrons containing only the ``light'' flavor quarks, $u$, $d$ and $s$. Most of these hadrons are produced at low transverse momentum ($p_{\rm T}$) and originate from soft QCD processes. In this work, the production of $\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ has been measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and in inelastic pp collisions at $\sqrt{s} = 5.02$ TeV. To this end, the excellent PID performance of the ALICE Time Of Flight detector (TOF) was exploited. The $p_{\rm T}$ spectra of pions, kaons and protons have been measured in a wide momentum range (from about 100 ${\rm MeV}/c$ to 12 ${\rm GeV}/c$) and as a function of centrality. Based on these fundamental measurements, it was possible to characterize the medium formed in the collision. Particle production at low $p_{\rm T}$ exhibits features typical of the collective evolution of a strongly interacting medium. At this energy, the largest radial flow velocity is observed. The thermal properties of the medium can be accessed by studying the relative particle abundances in the framework of Standard Hadronization Models. The Nuclear Modification Factor was computed to quantify the effect of parton energy loss in the QGP on high-$p_{\rm T}$ particle production. The results are interpreted in comparison to predictions from state-of-the-art models and to similar measurements at the LHC

Analysis of heavy-flavour particles in ALICE with the O

Precise measurements of heavy-flavour hadrons down to very low pT represent the core of the physics program of the upgraded ALICE experiment in Run 3 [1]. These physics probes are characterised by a very small signal-to-background ratio requiring very large statistics of minimum-bias events. In Run 3, ALICE is expected to collect up to 13 nb−1 of lead–lead collisions, corresponding to about 1 × 1011 minimum-bias events. In order to analyse this unprecedented amount of data, which is about 100 times larger than the statistics collected in Run 1 and Run 2, the ALICE collaboration is developing a complex analysis framework that aims at maximising the processing speed and data volume reduction [2]. In this paper, the strategy of reconstruction, selection, skimming, and analysis of heavy-flavour events for Run 3 will be presented. Some preliminary results on the reconstruction of charm mesons and baryons will be shown and the prospects for future developments and optimisation discussed

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb 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 Pb–Pb 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 p–Pb 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 −1 < 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

Measurement of inclusive J/ψ\psi pair production cross section in pp collisions at s=13\sqrt{s} = 13 TeV

International audienceThe production cross section of inclusive J/$\psi$ pairs in pp collisions at a centre-of-mass energy $\sqrt{s} = 13$ TeV is measured with ALICE. The measurement is performed for J/$\psi$ in the rapidity interval $2.5 0$. The production cross section of inclusive J/$\psi$ pairs is reported to be $10.3 \pm 2.3 {\rm (stat.)} \pm 1.3 {\rm (syst.)}$ nb in this kinematic interval. The contribution from non-prompt J/$\psi$ (i.e. originated from beauty-hadron decays) to the inclusive sample is evaluated. The results are discussed and compared with data

Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p−-Pb collisions

International audienceMeasurements of the production of electrons from heavy-flavour hadron decays in pp collisions at $\sqrt{s} = 13$ TeV at midrapidity with the ALICE detector are presented down to a transverse momentum ($p_{\rm T}$) of 0.2 GeV$/c$ and up to $p_{\rm T} = 35$ GeV$/c$, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p$-$Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the $p_{\rm T}$ range $0.5 < p_{\rm T} < 26$ GeV$/c$ at $\sqrt{s_{\rm NN}} = 8.16$ TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p$-$Pb collisions grow faster than linear with the self-normalised multiplicity. A strong $p_{\rm T}$ dependence is observed in pp collisions, where the yield of high-$p_{\rm T}$ electrons increases faster as a function of multiplicity than the one of low-$p_{\rm T}$ electrons. The measurement in p$-$Pb collisions shows no $p_{\rm T}$ dependence within uncertainties. The self-normalised yields in pp and p$-$Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations

Observation of medium-induced yield enhancement and acoplanarity broadening of low-pTp_\mathrm{T} jets from measurements in pp and central Pb−-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}}=5.02 TeV

International audienceThe ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high $p_{\rm T}$) hadron trigger in proton$-$proton and central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb$-$Pb collisions. Recoil jet distributions are reported for jet resolution parameter $R=0.2$, 0.4, and 0.5 in the range $7 < p_{\rm T,jet} < 140$ GeV$/c$ and trigger$-$recoil jet azimuthal separation $\pi/2 < \Delta\varphi < \pi$. The measurements exhibit a marked medium-induced jet yield enhancement at low $p_{\rm T}$ and at large azimuthal deviation from $\Delta\varphi\sim\pi$. The enhancement is characterized by its dependence on $\Delta\varphi$, which has a slope that differs from zero by 4.7$\sigma$. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation

Probing the Chiral Magnetic Wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC

International audienceThe Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic ($v_{2}$) and triangular ($v_{3}$) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope $r_{3}^{\rm Norm}$ is found to be larger than zero and to have a magnitude similar to $r_{2}^{\rm Norm}$, thus pointing to a large background contribution for these measurements. Furthermore, $r_{2}^{\rm Norm}$ can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW ($f_{\rm CMW}$) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for $f_{\rm CMW}$, and in the 10-60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level