Anisotropic flow and other collective phenomena measured in Pb-Pb collisions with ALICE at the LHC
Ilya Selyuzhenkov
备注：
Talk given at the International Symposium on Multiparticle Dynamics (ISMD 2011), 26-30 September 2011, AHiroshima (Miyajima Island), Japan; 6 pages, 5 figures
Recent results of the anisotropic flow measurements by the ALICE Collaboration at the LHC are reviewed. Directed, elliptic, triangular, and quadrangular flow are presented differentially vs. transverse momentum, pseudo-rapidity, and the collision centrality for charged and identified particles. Experimental probes of local parity violation using the charge dependent azimuthal correlations with respect to the reaction plane are also discussed.
We present recent results on short-lived hadronic resonances obtained by the ALICE experiment in pp, p-Pb and Pb-Pb collisions at LHC energies, including the most recent measurements of $Λ(1520)$ and $Ξ(1530)^{0}$ resonances.
ALICE is the experiment at the LHC collider at CERN dedicated to heavy ion physics. In this report, the ALICE detector will be presented, together with its expected performance as far as some selected physics topics are concerned.
We present the latest results on the ALICE performance for heavy-quark production and quenching measurements, focusing in particular on charm particles.
We present recent results on short-lived hadronic resonances obtained by the ALICE experiment at LHC energies. Results include system-size and collision-energy evolution of transverse momentum spectra, yields and ratios of resonance yields to those of longer lived particles, and nuclear modification factors. The results are compared with model predictions and measurements at lower energies.
In this paper, we summarize the perspectives on quarkonia detection in the ALICE experiment at the CERN LHC, both in the dielectron and dimuon decay channels.
We present the expected ALICE performance for the measurement of the p_t-differential cross section of electrons from beauty decays in central Pb-Pb collisions at the LHC.
We give a brief review of the physics of gluon saturation and non-linear QCD evolution at small values of the Bjorken-$x$ variable. We discuss the ALICE capability for low-$x$ studies at the LHC. In particular, we concentrate on the heavy quark production in the CGC framework and its observation with the ALICE Muon Spectrometer.
High energy p-p, p-Pb and Pb-Pb collisions at the CERN-LHC offer unprecedented opportunities for studying wide variety of physics at small Bjorken-x. Here we discuss capabilities of the ALICE experiment at the CERN-LHC for probing small-x QCD physics. A new forward electromagnetic calorimeter is being proposed as an ALICE upgrade to explore the small-x region in more detail.
We present recent results on short-lived hadronic resonances obtained by the ALICE experiment at LHC energies, including results from the Xe--Xe run. The ALICE results on transverse momentum spectra, yields, their ratio to long-lived particles, and nuclear modification factors will be discussed. The results will be compared with model predictions and measurements at lower energies.
The ALICE experiment is devoted to the study of heavy-ion collisions at the CERN LHC collider. We present the results of a feasibility study for the detection of D^0 \to K^-π^+ decays in Pb-Pb collisions with ALICE.
First experimental results are presented on event-by-event net-proton fluctuation measurements in Pb- Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, recorded by the ALICE detector at the CERN LHC. The ALICE detector is well suited for such studies due to its excellent particle identification capabilities and large acceptance, which is crucial for fluctuation analysis. The studies are focussed on second order cumulants, but the analysis technique used is more general and will be applied, in the near future, also to higher order cumulants.
The exclusive reconstruction of D^0 mesons in the ALICE experiment allows to study the QCD energy loss of charm quarks in the deconfined quark-gluon plasma (QGP) medium expected to be produced in central nucleus-nucleus collisions at the Large Hadron Collider.
ALICE is a general purpose experiment designed to investigate nucleus-nucleus collisions at the Large Hadron Collider (LHC), located at CERN. The ALICE detector is optimized for the reconstruction of quarkonia through the dimuon decay channel at foward rapidity as well as the dielectron decay channel at midrapidity. In this contribution, quarkonium measurements performed by the ALICE collaboration at both midrapidity and forward rapidity for various energies and colliding systems (pp, p-Pb and Pb-Pb), will be discussed and compared to theory.
We report on forward-rapidity charmonium production in pp collisions at a center of mass energy $\sqrt{s} = 13$ TeV, as measured by ALICE at the LHC. Differential cross sections for both J/ψ and ψ(2S) are presented as a function of the charmonium transverse momentum and rapidity. Results are compared to similar measurements performed by LHCb, to lower energy measurements and to state of the art model calculations.
ALICE is the Large Hadron Collider (LHC) experiment dedicated to the study of heavy ion collisions. The main purpose of ALICE is to investigate the properties of a new state of deconfined nuclear matter, the Quark Gluon Plasma (QGP). Quarkonium measurements will play a crucial role in this investigation due to the interplay of several competing mechanisms that are predicted to modify its production in the presence of a QGP. During the 2010 and 2011 LHC campaigns, ALICE took pp data at sqrt(s)=2.76 and 7 TeV and Pb-Pb data at sqrt(s_nn)=2.76 TeV. We present the latest results of J/psi productio…
We present recent result on strange and non-strange D-meson production measured with ALICE in Pb--Pb collisions at the LHC. In addition, the measurements of the $Λ_{\rm c}^+$-baryon production and of the $Λ_{\rm c}^+/{\rm D^0}$ ratio in pp, p--Pb, and, for the first time ever, Pb--Pb collisions are reported.
Latest results on open heavy favour measurements in pp collisions at 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV with the ALICE experiment are presented. The results of the single lepton analyses (electrons at central rapidity, muons at forward rapidity) and D meson reconstruction will be discussed.
ALICE will study nucleus-nucleus and proton-proton collisions at the LHC. The main goal of the experiment is to investigate the properties of QCD matter at the extreme energy densities that will be reached in Pb-Pb collisions. Heavy quarks (charm and beauty) are regarded as powerful tools for this study. After briefly reviewing the ALICE heavy-flavour program, we will describe the preparation for the first measurements to be performed with pp collisions.
Charged particle directed flow at midrapidity, |eta|<0.8, and forward rapidity, 1.7 < |eta|<5.1, is measured in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV with ALICE at the LHC. Directed flow is reported as a function of collision centrality, charged particle transverse momentum, and pseudo-rapidity. Results are compared to measurements at RHIC and recent model calculations for LHC energies.
The ALICE experiment will be able to detect hadrons containing charm and beauty quarks in proton-proton and heavy ion collisions in the new energy regime of the CERN Large Hadron Collider (LHC). Open charmed mesons are a powerful tool to study the medium produced in heavy ion collisions, since charm quarks are produced on a very short time scale and they experience the whole history of the collision. In addition, the measurements of heavy flavour yield provide a natural normalization for those of charmonia and bottomonia production at LHC. In this talk, after a general overview of ALICE perspe…
At LHC energy, heavy quarks will be abundantly produced and the design of the ALICE detector will allow us to study their production using several channels. The expected heavy-quark in-medium energy loss in nucleus-nucleus collisions at the LHC is calculated within a model, that is compared to the available heavy-quark quenching measurements at RHIC. The nuclear modification factors and heavy-to-light ratios of charm and beauty mesons are considered. The capability of the ALICE experiment for addressing this phenomenology is discussed.
The Transition Radiation Detector (TRD) for the ALICE experiment at the Large Hadron Collider (LHC) identifies electrons in p+p and in the challenging high multiplicity environment of heavy-ion collisions and provides fast online tracking for the ALICE Level1 trigger. The TRD is designed to have excellent position resolution and pion rejection capability. Presently, six of the 18 TRD supermodules are installed in the ALICE central barrel. In 2008, four supermodules were installed and commissioning of the detector using cosmic ray tracks was successfully performed. We briefly describe the desig…
We present the measurements of electrons and muons from the semi-leptonic decays of heavy-flavour hadrons measured in the central and forward rapidity regions with ALICE in pp, Pb-Pb, and p-Pb, collisions at the LHC. The pT-differential production cross section in pp collisions, the elliptic flow in Pb-Pb collisions, and the nuclear modification factor in Pb-Pb and p-Pb collisions are shown. The results are compared to theoretical predictions.
We present spectra of $π^0$, $η$ and $ω$ mesons in pp collisions and $π^{0}$ mesons in Pb-Pb collisions measured with ALICE at LHC energies. The $π^0$ and $η$ mesons are reconstructed via their two-photon decays by two complementary methods, using the electromagnetic calorimeters and photon conversion technique; both measurements show perfect agreement. We measure the nuclear modification factor ($R_{AA}$) of $π^0$ production in Pb-Pb collisions at different collision centralities and compare with lower energy results and theoretical predictions.
We present an overview of measurements related to open heavy-flavour production with the ALICE experiment at the LHC. Studies are performed using single leptons (electrons at mid-rapidity and muons at forward-rapidity) and D mesons, which are reconstructed via their hadronic decay channels. The measured differential production cross sections in proton-proton collisions at $\sqrt{s}$ = 2.76 and 7 TeV are in agreement with perturbative QCD calculations. Results from Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV on the nuclear modification factor $R_{AA}$ are shown, along with the elliptic flow …
A Monte Carlo study of two jet observables that can be used to obtain jet samples enhanced in quark or gluon content is presented. We compare the performance of one of these methods on pure Monte Carlo events with that after the transport of events through the full simulation of the ALICE experiment. It is shown that the performance of the method is not deteriorated by experimental effects like resolution and inefficiency.
Azimuthal di-hadron correlations play important role in the characterization of the medium created in heavy-ion collisions at RHIC. Moreover, as a novel phenomenon, strong modification of the away-side correlation is observed in Au+Au with respect to p+p collisions. Below the exclusive jet reconstruction threshold at LHC, leading particle correlations will provide access to the regime where hard scatterings and bulk medium properties can be simultaneously studied. Leading particle correlations can be extended to very low transverse momenta via the tracking and particle identification capabilit…
Mixed harmonic charge dependent azimuthal correlations at mid-rapidity in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV were measured with the ALICE detector at the LHC. A clear charge dependence for a series of correlations is observed both via the multi-particle cumulant and the event plane methods. Implications from these measurements for the possible effects of local parity violation in QCD and for models which incorporate azimuthal anisotropic flow and "effective" local charge conservation on the kinetic freeze-out surface are discussed.
Open heavy-flavour and quarkonia measurements are important tools to study the hot and dense partonic medium formed in ultra-relativistic heavy-ion collisions. The modification of their production in those collisions, with respect to the pp and p-Pb ones, can help in the characterization of this medium. Quarkonia and open heavy-flavour production is measured in ALICE in the three different collision systems, at mid- and forward rapidity. A selection of those results recently obtained in Pb-Pb and p-Pb collisions by the ALICE Collaboration is presented.
A Large Ion Collider Experiment (ALICE) is one of the four large experiments at the Large Hadron Collider (LHC), and it is dedicated to the study of ultra-relativistic heavy-ion collisions, with the goal of investigating the properties of the high-density state of QCD matter produced in these collisions. The study of D meson production azimuthal anisotropy and the measurement of their elliptic flow (v2) can provide insight on the degree of thermalisation of charm quarks in the medium and on the charm hadronization mechanism. We present the measurement of the D+ and D0 meson v2 in Pb-Pb collisi…
The ALICE Collaboration has measured heavy-flavour production through the reconstruction of hadronic decays of D mesons at mid-rapidity and via semi-electronic (at mid-rapidity) and semi-muonic (at forward rapidity) decays of charm and beauty hadrons in pp, p-Pb and Pb-Pb collisions. A summary of the most recent results from p-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV and Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV is presented in this paper.
We present the first results from the ALICE experiment on the nuclear modification factors for heavy-flavour hadron production in Pb-Pb collisions at sqrt{s_NN}=2.76 TeV. Using proton-proton and lead-lead collision samples at sqrt{s}=7 TeV and sqrt{s_NN}=2.76 TeV, respectively, nuclear modification factors R_AA(pt) were measured for D mesons at central rapidity (via displaced decay vertex reconstruction), and for electrons and muons, at central and forward rapidity, respectively.
ALICE is the dedicated heavy-ion experiment at the LHC. Its main physics goal is to study the properties of strongly-interacting matter at conditions of high energy density and high temperature expected to be reached in central Pb--Pb collisions. Charm and beauty quarks are well-suited tools to investigate this state of matter since they are produced in initial hard scatterings and are therefore generated early in the system evolution and probe its hottest, densest stage. ALICE recorded pp data at $\rm \sqrt{s}$ = 7 TeV and 2.76 TeV and Pb--Pb data at $\rm \sqrt{s}_{\rm NN}$=2.76 TeV in 2010 a…
Mixed harmonic charge dependent azimuthal correlations at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV were measured with the ALICE detector at the LHC. A clear charge dependence for a series of correlations is observed both via the multi-particle cumulant and the event plane methods. Implications from these measurements for the possible effects of the local parity violation in QCD and for models which incorporate the azimuthal anisotropic flow and the local charge conservation on the kinetic freeze-out surface are discussed.
The ALICE experiment has measured quarkonium production in Pb-Pb collisions at \sqrt{sNN} = 2.76 TeV and in p-Pb collisions at \sqrt{sNN} = 5.02 TeV. The measurements are performed in the dielectron de- cay channel at mid-rapidity (|yLAB| < 0.9) and in the dimuon decay channel at forward rapidity (2.5 < yLAB < 4). We focus in particular on the J/ψ nuclear modification factor measured both in Pb-Pb and p- -Pb collisions and on the Υ(1S) nuclear modification factor measured in Pb-Pb collisions.
The ALICE detector recorded Pb-Pb collisions at sqrtsNN = 2.76 TeV at the LHC in November-December 2010. We present the results of the measurements that provide a first characterization of the hot and dense state of strongly-interacting matter produced in heavy-ion collisions at these energies. In particular, we describe the measurements of the particle multiplicity, collective flow, Bose-Einstein correlations, high-momentum suppression, and their dependence on the collision centrality. These observables are related to the energy density, the size, the viscosity, and the opacity of the system.…
The baryon chemical potential $μ_B$ is a fundamental parameter for the statistical mechanical description of particle production in heavy-ion collisions: its value encodes the average net baryon content of the fireball at chemical freeze-out. The first $μ_B$ measurement in high-energy Pb-Pb collisions at the LHC was published in 2018 in Nature, and it was found that $μ_B=0.7\pm3.8$ MeV. In this contribution, an improved $μ_B$ measurement based on the study of antiparticle-to-particle ratios for protons, $^3\mathrm{He}$ and hypertriton ($^3_Λ\mathrm{H}$) using the data collected by ALICE in Run…
The ALICE experiment at LHC is mainly dedicated to heavy-ion physics. An overview of its performances, some predictions related to its first measurements and QGP observable measurements will be given.
Charmonium states are considered important signatures of the strongly interacting medium created in heavy-ion collisions. In the ALICE experiment, these probes can be investigated in the mu^+mu^- decay channel, in the forward rapidity region (2.5<y<4) down to zero transverse momentum. Results on charmonia production in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV are presented. The centrality and transverse momentum dependence of the inclusive J/Psi nuclear modification factor are shown and compared with theoretical models. Finally, first ALICE results on the Psi(2S) production in Pb-Pb collisions …
Measurements of the production of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4.0$) in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ and 5.02 TeV with the ALICE detector are presented along with the $R_{\rm AA}$ measurements in different centrality intervals as a function of transverse momentum, $p_{\rm T}$. Results of the measured $R_{\rm AA}$ at both energies are shown and are compared to the different model predictions.
The ALICE experiment at the Large Hadron Collider LHC is presented, and an overview of its physics program is given. A few specific observables are discussed in order to illustrate the physics potential of ALICE.
The strong suppression of high-$p_T$ hadrons observed in heavy ion collisions at RHIC indicates the interaction of high energy partons with a dense colored medium prior to hadronization. We review the main results from the high-$p_T$ hadron analysis at RHIC and what they tell us about the medium. We then concentrate on the new possibilities that the wider kinematic range at the LHC will offer and how they will help us to better characterize the medium produced in these collisions.
The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of a central barrel, a muon spectrometer and additional detectors for trigger and event classification purposes. The low transverse momentum threshold of the central barrel gives ALICE a unique opportunity to study the low mass sector of central exclusive production at the LHC.
The ALICE collaboration has studied inclusive J/$ψ$ and $ψ$(2S) production at forward rapidities in pp collisions at $\sqrt{s} = 7$ TeV with the ALICE Muon Spectrometer. The analysis has been carried out on a data sample corresponding to an integrated luminosity $\mathcal{L}_{\rm int}$ = 1.35 pb$^{-1}$. The production cross-sections of J/$ψ$ and $ψ$(2S), integrated over \pt\ (0 $<$ \pt\ $<$ 20 GeV/$c$) and \y\ (2.5 $<$ \y\ $<$ 4), have been measured. The J/$ψ$ and $ψ$(2S) differential cross-sections, in transverse momentum and rapidity, have also been measured. The results have been compared w…
The ALICE Collaboration collected a large data sample of Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV in 2015 at the Large Hadron Collider (LHC) and the excellent particle identification (PID) capabilities allow for the detection of rarely produced (anti-)hypernuclei. In particular, the (anti-)hypertriton, $^3_Λ$H, which is a bound state of a proton, a neutron and a $Λ$, is the lightest known hypernucleus. The results on the $^3_Λ$H production are compared with the predictions from a model based on coalescence approach and from statistical-thermal models to investigate the production me…
Recent multiplicity-dependent analyses of pp and p--Pb collision data have revealed that particle production shares similar features with that in heavy-ion collisions. Studies using resonances could help to understand the possible onset of collective-like phenomena and the presence of a hadronic phase in small collision systems. Measurements of the differential yields of resonances with different lifetime, mass, quark content, and quantum numbers could enable understanding the mechanisms that influence the shape of particle momentum spectra, lifetime of the hadronic phase, strangeness producti…
In 2013, inclusive J/psi measurements in p-Pb collisions were performed at the LHC at sqrt(sNN) = 5.02 TeV, in order to measure the effects related to the cold nuclear matter on the J/psi production. Their evaluation is important in order to be able to disentangle hot and cold nuclear matter effects in Pb-Pb collisions. In this contribution, results on the inclusive J/psi production in p-Pb collisions, in the dimuon decay channel at forward and backward rapidity, down to zero transverse momentum, are presented and compared to theoretical models.
Measurements of direct photon and neutral pion production in heavy-ion collisions provide a comprehensive set of observables characterizing properties of the hot QCD medium. Direct photons provide means to test the initial stage of an AA collision and carry information about the temperature and space-time evolution of the hot medium. Neutral pion suppression probes the parton energy loss in the hot medium. Measurements of neutral meson spectra in pp collisions at LHC energies $\sqrt{s}=$0.9, 2.76, 7 TeV serve as a reference for heavy-ion collisions and also provide valuable input data for para…
ALICE is an LHC experiment devoted to the study of strongly interacting matter in proton-proton, proton--nucleus and nucleus-nucleus collisions at ultra-relativistic energies. The ALICE VZERO system, made of two scintillator arrays at asymmetric positions, one on each side of the interaction point, plays a central role in ALICE. In addition to its core function as a trigger, the VZERO system is used to monitor LHC beam conditions, to reject beam-induced backgrounds and to measure basic physics quantities such as luminosity, particle multiplicity, centrality and event plane direction in nucleus…
We present a measurement of the nuclear modification factor of electrons from heavy- flavour hadron decays at midrapidity in Pb-Pb collisions at {\surd}sNN = 2.76 TeV. Electrons are identified in the pt range 1.5 GeV/c < pt < 6 GeV/c. A suppression is seen for pt larger than 3.5 GeV/c in the most central collisions.
ALICE has been specifically optimized to study heavy-ion collisions at the LHC, up to a charged particle density of 8000 per unit of rapidity in central heavy-ion collisions at $\sqrt{s_{NN}}$ = 5.5 TeV. The High Momentum Particle Identification Detector (HMPID) has a proximity focusing geometry with a liquid $\rm C_{6}F_{14}$ Cherenkov radiator coupled to Multi-Wire Pad Chambers (MWPC) equipped with CsI photocathodes, over a total active area of 11 $\rm m^2$. It has been designed to identify charged pions and kaons in the range 1 $\leq p \leq$ 3 \GeV/$c$ and protons in the range 2 $\leq p \le…
ALICE (A Large Ion Collider Experiment) is the LHC experiment dedicated to the investigation of the nature and the properties of the Quark-Gluon Plasma (QGP) using heavy-ion collisions. Among its characteristics, excellent particle identification capabilities stand out, which are a basic requirement to address QGP physics. The ALICE particle identification performance will be reviewed in this paper, focusing in particular on the LHC Run 2 period.
Reconstruction of jets in high-energy heavy-ion collisions is challenging due to the large and fluctuating background coming from the underlying event. We report results on full jet reconstruction, obtained from data collected in 2011 by the ALICE detector at LHC for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76~\mathrm{TeV}$. The analysis makes use of the tracking system and the electromagnetic calorimeter. Signal jets, which come from hard scattered partons, are reconstructed using the anti-$k_{\mathrm{T}}$ jet finder algorithm. The average background is subtracted on a jet-by-jet basis t…
Measurements of charm and beauty production in pp collisions, using the ALICE detector system, at LHC energies ($\sqrt{s} = 2.76$ and 7.0 TeV) can test perturbative QCD down to very low Björken-x. They are also critical as a reference to ALICE's heavy ion program. The ALICE detector system allows measurements not covered by the other LHC experiments in addition to covering complementary regions. A description of the ALICE detector system, in relation to ATLAS and CMS, are presented. Results from both leptonic and hadronic decay channels will be shown along with comparisons to other measurement…
The measurement of D-meson production in heavy-ion collisions at LHC energy provides insights into the mechanisms of interaction of charm quarks in the hot and dense medium formed in these collisions. ALICE results on the D-meson nuclear modification factor and azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV are presented.
After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data with proton collisions at the LHC starting in November 2009 and first Pb-Pb data in November 2010. This article summarizes initial operation and performance of ALICE as well as first results from both pp and Pb-Pb collisions.
Results on open heavy-flavour production in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV measured with ALICE at the LHC are presented. The nuclear modification factors, extracted in three different channels, show a strong suppression in central collisions. The measured D-meson azimuthal anisotropy indicates a non-zero v2, which is similar to the one of charged hadrons.
