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Topical conference on Strangeness and Heavy Flavor production in Heavy-Ion Collisions
The conference will focus on new experimental and theoretical developments on the role of strange and heavy-flavour quarks in proton-proton and in heavy-ion collisions, and in astrophysical phenomena. New results are expected, from the LHC, from RHIC and from other experimental programs.
The 16th International Conference on Strangeness in Quark Matter, follows the recent events of 2015 in Dubna, 2013 in Birmingham, and 2011 in Cracow.
Topics include:
Hadrons carrying heavy quarks, i.e. charm or bottom, are
important probes of the hot and dense medium created in relativistic
heavy-ion collisions. Heavy quark-antiquark pairs are mainly produced
in initial hard scattering processes of partons. While some of the
produced pairs form bound quarkonia, the vast majority hadronize into
particles carrying open heavy flavor. The PHENIX Collaboration carries
out a comprehensive physics program which studies open heavy flavor
and quarkonium production in relativistic heavy-ion collisions at
RHIC. The discovery at RHIC of large high-pT suppression and flow of
electrons from heavy quarks flavors have altered our view of the hot
and dense matter formed in central Au+Au collisions at 200 GeV. These
results suggest a large energy loss and flow of heavy quarks in the
hot, dense matter. In recent years, the PHENIX has installed a silicon
vertex tracker both in central rapidity (VTX) and in forward rapidity
(FVTX) regions, and has collected large data samples. These two
silicon trackers enhance the capability of heavy flavor measurements
via precision tracking.
This talk summarizes the latest PHENIX results concerning open and
closed charm and beauty heavy quark production as a function of
rapidity, energy and system size, and their interpretation with
respect to the current theoretical understanding on this topic.
Exploiting the (nearly) full gamut of particles emitted in nucleon- and heavy-ion
induced reactions at few-GeV energies, the HADES experiment at GSI is pursuing
a systematic investigation of cold and hot nuclear matter effects.
I will give an update on the current and planned HADES physics program,
with a particular emphasis on open and hidden strangeness observables.
The main goal of the ALICE experiment is the characterization of the Quark Gluon Plasma (QGP), the hot and dense matter created in high-energy nuclear collisions.
Heavy quarks (charm and beauty) are unique probes of the QGP because they are produced in hard partonic scattering processes occurring in the initial stage of the collisions, they propagate through the medium and interact with its constituents, thus probing the entire evolution of the system.
The heavy-flavour in-medium energy loss and elliptic flow are among the key observables to investigate the properties of the QGP, providing a test of the colour-charge and parton-mass dependence of in-medium energy loss and an effective tool to investigate to what extent heavy quarks participate in the collective motion in the medium.
The measurement of the heavy-flavour production in p--Pb collisions provides insight into the role of cold nuclear matter effects.
The ALICE detector provides precise tracking and vertexing and charged particle identification over a broad momentum range. These capabilities allow us to study open charm via the reconstruction of the $\rm D^{0}$, $\rm D^{*}$, $\rm D^{+}$ and $\rm D_{s}$ hadronic decay channels at mid-rapidity. Furthermore, open heavy-flavour production is accessible via semi-leptonic decays of charm and beauty hadrons, both at mid-rapidity (electrons) and at forward rapidity (muons).
In this contribution we will present the ALICE measurements of D-meson and heavy-flavour decay lepton production in Pb--Pb and p--Pb collisions. In particular, we will review the main results from recent publications of D-meson spectra and heavy-flavour decay lepton spectra, nuclear modification factors and elliptic flow in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV, in different collision centralities. We will discuss the comparison with the results obtained in p--Pb, with other hadron species and with theoretical model calculations. Furthermore, we will present results from an extension of the $\rm{D}^{0}$ production measurement down to zero transverse momentum in p--Pb collisions and of the total charm production cross section at mid-rapidity. We will also introduce the prospects for open heavy-flavour analyses from Run 2 at the LHC.
We analyze hadrochemical freeze-out in central collisions of mass 200 nuclei, at AGS, SPS and LHC energies. Ideally, the hadronic multiplicities are the outcome of QCD hadronization, which creates them in Grand Canonical(GC) equilibrium of species essentially due to phase space dominance. The GC analysis performed in the Statistical Hadronization Model(SHM) thus ideally reveals points along the QCD phase boundary line, in the (T,mu(B)) plane which is common to Lattice QCD at finite baryochemical potential mu(B), and to the SHM. Within these assumptions one of the main goals common to QCD theory and nuclear collision experiments comes well within reach.
This picture requires some correction as it turns out that the model of an instantaneous, synchronous chemical freeze-out occuring at hadronization does not meet with reality in A+A collisions due to the large hadron/resonance density right after hadronization. Inelastic transmutations of species does in fact play no essential role owing to the "low" phase transition temperature, but baryon-antibaryon annihilation processes do persist throughout the final hadron/resonance expansion phase. We have quantified these effects employing the microscopic transport model UrQMD. A rather substantial proton-antiproton annihilation rate to pions is observed at all energies, explaining the much debated "non-thermal proton to pion ratio" first observed at the LHC.
After entering the yield modifications predicted by UrQMD into the SHM analysis we recover the "true" positions of the hadronization points in the (T,mu(B)) plane. A very low curvature of the QCD transition line is indicated up to about mu(B)=400MeV
in agreement with lattice calculations, followed by a sudden drop-off at the AGS.
Further data at lower energy are urgently expected from NA61,FAIR and NICA.
Proton-proton (pp) collisions have been used extensively as a reference for the study of interactions of larger colliding systems at the LHC.
Recent measurements performed in high-multiplicity pp and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions.
In this context, the study of identified particle spectra and yields as a function of multiplicity is a key tool for the understanding of similarities and differences between small and large systems.
We report on the production of pions, kaons, protons, K$^{0}_{\rm S}$, $\Lambda$, $\Xi$, $\Omega$, K$^{*0}$ and $\phi$ as a function of multiplicity in pp collisions at $\sqrt{s}=7TeV$ measured with the ALICE experiment.
The work presented here represents the most comprehensive set of results on identified particle production in pp collisions at the LHC.
Spectral shapes, studied both for individual particles and via particle ratios as a function of $p_{\rm T}$, exhibit an evolution with charged particle multiplicity that is similar to the one observed in larger systems.
The production rates of strange hadrons are observed to increase more than those of non-strange particles, showing an enhancement pattern with multiplicity which is remarkably similar to the one measured in p-Pb collisions.
This enhancement seems to be driven by the number of strange quarks inside the hadron and cannot be satisfactorily reproduced by any Monte Carlo generator currently in use at the LHC.
In addition, results on the production of light flavour hadrons in pp collisions at $\sqrt{s}=13TeV$, the highest centre-of-mass energy ever reached in the laboratory, are also presented and the changes observed as a function of $\sqrt{s}$ are discussed.
The key question of whether or not the observed evolution of bulk particle production with increasing $\sqrt{s}$ is mostly driven by an increase in charged particle density is also addressed.
The production of charmonium states, as the $J/\psi$ and $\psi(2S)$, in heavy-
ion collisions, is an important probe to investigate the formation of a plasma
of quarks and gluons (QGP). In a hot and deconfined medium, quarkonium
production is, indeed, expected to be significantly modified, with respect to
the pp yields scaled by the number of binary nucleon-nucleon collisions, due
to a balance of color screening and charm quark (re)combination mechanisms.
The ALICE Collaboration at the LHC, has measured charmonium production in Pb-Pb collisions at two center of mass energies, $\sqrt(s_{NN})$= 2.76 and 5.02
TeV. The nuclear modication factor of inclusive $J/\psi$, evaluated at both
mid (|y| <0.8) and forward (2.5< y <4) rapidities, is measured as a function of the centrality of the collision and of the $J/\psi$ kinematic variables as
transverse momentum and rapidity.
In this presentation, we will report on the final results on $J/\psi$ and $\psi(2S)$
production at $\sqrt(s_{NN}$= 2.76 TeV and on the new $J/\psi$ results, obtained at
forward rapidity, at $\sqrt(s_{NN})$= 5.02 TeV. These new results will be compared
with the $J/\psi$ nuclear modication factor obtained at lower energy and with
the available theoretical predictions.
Heavy quarkonia are an essential probe in understanding the properties of the quark-gluon plasma (QGP) formed
in relativistic heavy-ion collisions. The suppression of $J/\psi$ in the medium due to color-screening has been proposed
as a direct signature of the QGP formation.
However, its production mechanism in p+p collisions have not been fully understood despite of decades of efforts,
which warrants more measurements. Moreover, the contribution from regenerated $J/\psi$ by the coalescence of
uncorrelated $c$ and $\bar{c}$ quarks in the medium can add an additional complication to the interpretation of observed
$J/\psi$ suppression in Au+Au collisions. Precise measurements of $J/\psi$ production in p+p collisions, and the nuclear
modification factor ($R_{AA}$) and elliptic flow ($v_2$) in a wide $p_T$ range in Au+Au collisions, can help better understand
different production mechanisms in such collisions. On the other hand, $\Upsilon$ states are cleaner probes
since the regeneration contribution is negligible at RHIC energies.
The newly installed Muon Telescope Detector, which provides muon identification capability at mid-rapidity, opens the door to
measure quarkonia via the di-muon channel at STAR.
In this talk, we will present (1) measurements of $J/\psi$ production in p+p collisions at $\sqrt{s}=500$ GeV sampled during RHIC 2013 run,
including its cross-section and yield dependence on event multiplicity; (2) measurements of $R_{AA}$ and $v_2$ of $J/\psi$ , and the production
of $\Upsilon$ states in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV, based on the full data sample taken in RHIC 2014 run.
ATLAS measurement of azimuthal correlations between particle pairs at large pseudorapidity separation in pp and pPb collisions are presented. The data were collected using a combination of the minimum-bias and high track-multiplicity triggers. A detailed study of the dependence of two-particle correlations on the charged particle multiplicity, transverse momentum of the pair constituents and the pseudorapidity separation between particles forming a pair is shown. Measurements of multi-particle cumulants in the azimuthal angles of produced particles in wide pseudorapidity (|η|<2.5) and multiplicity ranges, with the aim to extract a single particle anisotropy coefficient, v1-v5, are also presented. These measurements can help to understand the origin of the long-range correlations seen in high-multiplicity pp and p+Pb collisions.