A novel attempt has been made to probe the QCD phase boundary by using the experimental data for transverse momenta of ϕ mesons produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted with simple thermodynamic expectations and lattice QCD results. The experimental data indicate a first-order phase transition, with a mixed phase stretching the energy density between \sim1 and 3.2 GeV/fm3 corresponding to SPS energies.
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.
An experimental overview of anisotropic flow measurements and their ability to probe the properties and the nature of the system created in ultra-relativistic hadron collisions is given in these proceedings. The aim is to discuss the state-of-the-art measurements ranging from small to large systems at different collision energies.
We explore the system size dependence of heavy-quark-QGP interaction by studying the heavy flavor meson suppression and elliptic flow in Pb-Pb, Xe-Xe, Ar-Ar and O-O collisions at the LHC. The space-time evolution of the QGP is simulated using a (3+1)-dimensional viscous hydrodynamic model, while the heavy-quark-QGP interaction is described by an improved Langevin approach that includes both collisional and radiative energy loss inside a thermal medium. Within this framework, we provides a reasonable description of the $D$ meson suppression and flow coefficients in Pb-Pb collisions, as well as …
The determination of the color force in a quark-gluon plasma (QGP) is a key objective in the investigation of strong-interaction matter. Open and hidden heavy-flavor observables in heavy-ion collisions (HICs) are believed to provide insights into this problem by comparing calculations of heavy-quark (HQ) and quarkonium transport with pertinent experimental data. In this work, we utilize the $T$-matrix formalism to compute charm-quark transport coefficients for various input potentials previously extracted from simultaneous fits to lattice-QCD data for HQ free energies, quarkonium correlators a…
The modifications of $D_s$-meson spectra in ultrarelativistic heavy-ion collisions are identified as a quantitative probe of key properties of the hot nuclear medium. This is enabled by the unique valence-quark content of the $D_s$=$c\bar{s}$ which couples the well-known strangeness enhancement with the collective-flow pattern of primordially produced charm quarks. We employ a consistent strong-coupling treatment with hydrodynamic bulk evolution and nonperturbative $T$-matrix interactions for both heavy-quark diffusion and hadronization in the Quark-Gluon Plasma (QGP). A large enhancement of t…
The tiny droplets of Quark Gluon Plasma (QGP) created in high-energy nuclear collisions experience fast expansion and cooling with a lifetime of a few $\text{fm}/c$. Despite the information provided by probes such as jet quenching and quarkonium suppression, and the excellent description by hydrodynamical models, direct access to the time evolution of the system remains elusive. We point out that the study of hadronically-decaying $W$ bosons, notably in events with a top-antitop quark pair, can provide key novel insight, into the time structure of the QGP. This is because of a unique feature, …
We assess transport properties of heavy quarks in the Quark-Gluon Plasma (QGP) using static heavy-quark (HQ) potentials from lattice-QCD calculations in a Brueckner many-body T-matrix approach to evaluate elastic heavy-quark-light-quark scattering amplitudes. In the attractive meson and diquark channels resonance states are formed for temperatures up to ~1.5 T_c, increasing pertinent drag and diffusion coefficients for heavy-quark rescattering in the QGP beyond the expectations from perturbative-QCD calculations. We use these transport coefficients, complemented with perturbative elastic HQ gl…
Hadronic resonances, having very short lifetime, like $\rm{K}^{*0}$, can act as useful probes to understand and estimate lifetime of hadronic phase in ultra-relativistic proton-proton, p--Pb and heavy-ion collisions. Resonances with relatively longer lifetime, like $ϕ$ meson, can serve as a tool to locate the QGP phase boundary. We estimate a lower limit of hadronic phase lifetime in Cu--Cu and Au--Au collisions at RHIC, and in pp, p--Pb and Pb--Pb collisions at different LHC collision energies. Also, we obtain the effective temperature of $ϕ$ meson using Boltzmann-Gibbs Blast-Wave function, w…
Including O(m_c) terms in the coefficient functions and/or O(m_D) twist 3 contributions in the heavy meson distribution amplitudes leads to a non-zero transverse amplitude for exclusive neutrino production of a D pseudoscalar charmed meson on an unpolarized target. We work in the framework of the collinear QCD approach where chiral-odd transversity generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions.
Charm- and bottom-quark rescattering in a Quark-Gluon Plasma (QGP) is investigated with the objective of assessing the approach towards thermalization. Employing a Fokker-Planck equation to approximate the collision integral of the Boltzmann equation we augment earlier studies based on perturbative parton cross sections by introducing resonant heavy-light quark interactions. The latter are motivated by recent QCD lattice calculations which indicate the presence of "hadronic" states in the QGP. We model these states by colorless (pseudo-) scalar and (axial-) vector D- and B-mesons within a heav…
Charm quarks are an excellent probe to study properties of the Quark-Gluon Plasma (QGP) created in ultra-relativistic heavy-ion collisions. In particular, measurements of the $D_{s}^{\pm}$ meson production can provide valuable information on the charm quark hadronization mechanism in the QGP. We report the measurements from the STAR experiment on the invariant yields of $D_{s}^{\pm}$ mesons as a function of transverse momentum for different centrality classes of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. These measurements utilize the data with the Heavy Flavor Tracker detector from…
The main goal of the experimental programs on ultra-relativistic heavy ion collisions at the LHC is the production and characterization of the Quark Gluon Plasma (QGP), a phase of nuclear matter in which strongly interacting constituents (quarks and gluons) are deconfined. Heavy quarks are considered effective probes of the properties of the QGP as they are created on a short time scale, with respect to that of the QGP, and subsequently interact with it. Moreover, for a proper assessment of the characteristics of the matter produced in heavy-ion collisions, it is important to disentangle the f…
The study of heavy-flavour (charm and beauty) production is important to understand the properties of the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions, since heavy quarks are produced in the initial stages of the collisions and subsequently interact with the medium throughout its evolution. In the QGP, strange quarks are expected to be abundantly produced and may recombine with charm quarks leading to an enhancement of the nuclear modification factor ($R_{\rm AA}$) of ${\rm D}_{\rm s}^{+}$ mesons compared to that of other charmed meson states at low and intermedia…
The production of light neutral mesons in AA collisions probes the physics of the Quark-Gluon Plasma (QGP), which is formed in heavy-ion collisions at the LHC. More specifically, the centrality dependent neutral meson spectra in AA collisions compared to its spectra in minimum-bias pp collisions, scaled with the number of hard collisions, provides information on the energy loss of partons traversing the QGP. The measurement allows to test with high precision the predictions of theoretical model calculations. In addition, the decay of the $π^{0}$ and $η$ mesons are the dominant backgrounds for …
Transversity generalized parton distributions (GPDs) can be probed in diffractive electro- and photoproduction of two vector mesons on a hadron in kinematics where the two vector mesons are separated by a large rapidity gap. We report on calculations for this process in the case of coherent $ρ^0-ω$ meson production on a deuteron target. Our cross section results show that an electron-ion collider with deuteron beams and forward detectors could probe deuteron transversity GPDs.
Studies of quarkonium production in heavy-ion collisions can be used for probing QGP properties. The suppression and regeneration of bound quarkonium states is sensitive to the medium properties. Modifications of the quarkonium polarization in Pb-Pb collisions with respect to pp collisions may give further insight into the suppression and regeneration mechanisms in the QGP. Quarkonia are also sensitive to the initial stages of heavy-ion collisions, and measurements in photonuclear collisions may help constrain the nuclear gluon-distribution at low Bjorken-$x$. In this work, recent quarkonium m…
Heavy quarks, like charm and beauty, are sensitive probes to investigate the colour-deconfined medium created in high-energy heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of D$^{0}$, D$^{+}$, D$^{*+}$ and D$_{\mathrm{s}}^{+}$ in Pb-Pb collisions at $\sqrt{s_{\rm {NN}}}$ = 5.02 TeV. The measurement of the nuclear modification factor ($R_{\rm {AA}}$) provides informations on the in-medium parton energy loss. In addition, the comparison between D$_{\mathrm{s}}^{+}$ and the non-strange D-meson $R_{\rm {AA}}$ allows to investigate possible modif…
We present the measurements of the $ϕ$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV. The data are collected using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factor ($R_{\rm{CP}}$) of $ϕ$ meson is presented. The $ϕ$-meson $R_{\rm{CP}}$ has a value $\geq$ 1.0 for $\sqrt{s_{NN}}$ $\leq$ 39 GeV. The $Ω/ϕ$ ratios are also presented and show a different trend at the intermediate transverse momentum ($p_{T}$) for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. The num…
We investigate the heavy flavor dynamics in the quark-gluon plasma (QGP) medium created in p-Pb collisions at the CERN Large Hadron Collider (LHC). In the (3+1)-dimensional viscous hydrodynamics model describing QGP medium, the dynamics of heavy quarks are studied in an improved Langevin framework incorporating both collisional and radiative energy loss. The hadronization of the heavy quarks is given by a hybrid model of fragmentation and recombination. We find that the in-medium evolution of charm quarks raises the D-meson $R_{pPb}$ at low transverse momenta while it suppresses the D-meson $R…
The production of light neutral mesons in different collision systems is interesting for a variety of reasons: In nucleus-nucleus (AA) collisions the measurements provide important information on the energy loss of partons traversing the Quark-Gluon Plasma (QGP) which is formed in heavy-ion collisions at the LHC. In proton--proton (pp) collisions, neutral mesons allow us to test with high precision the predictions of perturbative QCD and other model calculations, and also serve as a reference for pA and AA collisions. In pA collisions, cold nuclear matter effects are studied. In the ALICE expe…
In this contribution, the nuclear modification factor and azimuthal anisotropy of prompt charm mesons and baryons in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV by the ALICE Collaboration are presented. Heavy quarks are a very suitable probe to investigate the quark-gluon plasma (QGP) produced in heavy-ion collisions, since they are mainly produced in hard-scattering processes and hence in shorter timescales compared to the QGP. Measurements of charm-hadron production in nucleus-nucleus collisions are therefore useful to study the properties of the in-medium charm-quark energy loss via…
Heavy-flavour hadrons are effective probes to study the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions. The ALICE Collaboration measured the D-mesons (D$^{0}$, D$^{+}$, D*$^{+}$ and D$^{+}_{\text s}$) production in Pb-Pb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV. The in-medium energy loss can be studied by means of the nuclear modification factor ($R_{\text{AA}}$). The comparison between the D$^{+}_{\text s}$ and the non-strange D-meson $R_{\text{AA}}$ can help to study the hadronisation mechanism of the charm quark in the QGP. In semi-central collisions the m…
One of the key signatures of the Quark Gluon Plasma (QGP) is the modification of hadron and direct photon spectra in heavy-ion collisions as compared to proton-proton (pp) collisions. Suppression of hadron production at high transverse momenta in heavy-ion collisions can be explained by the energy loss of the partons produced in the hard scattering processes which traverse the hot and dense QCD matter. The dependence of the observed suppression on the transverse momentum (pT) of the measured hadron towards higher pT is an important input for the theoretical understanding of jet quenching effec…
We study vector meson photoproduction from the deuteron at high momentum transfer, accompanied by break-up of the deuteron into a proton and neutron. The large $-t$ involved allows one of the nucleons to be identified as struck, and the other as a spectator to the $γN\rightarrow VN$ subprocess. Corrections to the plane wave impulse approximation involve final state interactions (FSIs) between the struck nucleon or the vector meson, either of which is energetic, with the slow spectator nucleon. In this regime, the eikonal approximation is valid, so is employed to calculate the cross-section for…
One of the key signatures of the Quark-Gluon Plasma (QGP) is the modification of hadron transverse momentum differential cross-sections in heavy-ion collisions (HIC) as compared to proton-proton (pp) collisions. Suppression of hadron production at high transverse momenta ($p_{\rm T}$) in HIC has been explained by the energy loss of the partons produced in the hard scattering processes which traverse the deconfined quantum chromodynamic (QCD) matter. The dependence of the observed suppression on the $p_{\rm T}$ of the measured hadron towards higher $p_{\rm T}$ is an important input for the theo…
We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of a Boltzmann transport approach. Non-perturbative interaction between heavy quarks and light quarks have been taken into account through a quasi-particle approach in which light partons are dressed with thermal masses tuned to lQCD thermodynamics. Such a model is able to describe the main feature of the non-perturbative dynamics: the enhancement of the interaction strength near $T_c$. We show that the resulting charm in-medium evolution is able to correctly predict simultaneously the nuclear suppression fact…
One of the key signatures of the Quark-Gluon Plasma (QGP), is the modification of hadron transverse momentum differential cross-sections in heavy-ion collisions (HIC) as compared to proton-proton (pp) collisions. Suppression of hadron production at high transverse momenta (\pt)~in HIC has been explained by the energy loss of the partons produced in the hard scattering processes which traverse the deconfined quantum chromodynamic (QCD) matter. The dependence of the observed suppression on the \pt~ of the measured hadron towards higher \pt~ is an important input for the theoretical understanding…
Heavy-flavour hadrons are recognised as a powerful probe for the characterisation of the deconfined medium created in heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of ${\rm D}^{0}$, ${\rm D}^{+}$, ${\rm D}^*$ and ${\rm D_s}^{+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02~{\rm TeV}$. The measurement of the nuclear modification factor ($R_{\rm AA}$) provides a strong evidence of the in-medium parton energy loss. The comparison between the ${\rm D_s}^{+}$ and the non-strange D-meson $R_{\rm AA}$ can help to study the hadronisation m…
We present the measurements of strange hadron elliptic flow at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The transverse momentum and collision centrality dependence of elliptic flow is presented. At the intermediate transverse momentum $Ω$ baryon and $ϕ$-meson show baryon-meson separation effect similar to proton and pion for minimum-bias Au+Au collision at $\sqrt{s_{NN}}$ =200 GeV. This indicates formation of collective flow at the early partonic phase. The separation between baryons and mesons at intermediate tra…
