The Color String Percolation Model (CSPM) is used to determine the shear viscosity to entropy ratio ($η/s$) of the Quark-Gluon Plasma (QGP) produced in Au-Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at RHIC and Pb-Pb at $\sqrt{s_{NN}}$ = 2.76 TeV at LHC. The relativistic kinetic theory relation for $η/s$ is evaluated using CSPM values for the temperature and the mean free path of the QGP constituents. The experimental charged hadron transverse momentum spectrum is used to determine the percolation density parameter $ξ$ in Au-Au collisions (STAR). For Pb-Pb at $\sqrt{s_{NN}}$ = 2.76 TeV $ξ$ values are obtained from the extrapolation at RHIC energy. The value of $η/s$ is 0.204$\pm$0.020 and 0.262$\pm$0.026 at the CSPM initial temperatures of 193.6$\pm$3 MeV (RHIC) and 262.2 $\pm$13 MeV (LHC) respectively. These values are 2.5 and 3.3 times the AdS/CFT conjectured lower bound $1/4π$. We compare the CSPM $η/s$ analytic expression with weak coupling (wQGP) and strong coupling (sQGP) calculations. This indicates that the QGP is a strongly coupled fluid in the phase transition region.
We review the current status of jet measurements in heavy-ion collisions at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). We discuss how the current measurements provide information about the quark-gluon plasma and discuss near future opportunities at both RHIC and the LHC.
In this article, we briefly review the recent progress related to extracting the quark-gluon plasma (QGP) specific shear viscosity from the flow data measured at Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC).
The progress over the 30 years since the first high-energy heavy-ion collisions at the BNL-AGS and CERN-SPS has been truly remarkable. Rigorous experimental and theoretical studies have revealed a new state of the matter in heavy-ion collisions, the quark-gluon plasma (QGP). Many signatures supporting the formation of the QGP have been reported. Among them are jet quenching, the non-viscous flow, direct photons, and Debye screening effects. In this article, selected signatures of the QGP observed at RHIC and the LHC are reviewed.
Thermalization and collective flow of charm (c) and bottom (b) quarks are evaluated from elastic parton scattering via "D"- and "B"-meson resonances in an expanding, strongly interacting quark-gluon plasma at RHIC. Pertinent drag and diffusion coefficients are implemented into a relativistic Langevin simulation to compute transverse-momentum spectra and azimuthal flow asymmetries (v_2) of c- and b-quarks. Upon hadronization (including coalescence and fragmentation) and semileptonic D- and B-decays, the resulting electron spectra (R_{AA} and v_2) are compared to recent RHIC data.
The Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the QGP produced in central Au-Au collisions at $\sqrt{s_{NN}}$ = 200 A GeV using STAR data at RHIC. When the initial density of interacting colored strings exceeds the 2D percolation threshold a cluster is formed, which defines the onset of color deconfinement. These interactions also produce fluctuations in the string tension which transforms the Schwinger particle (gluon) production mechanism into a maximum entropy thermal distribution. The single string tension is determined by identifying the kno…
Polarization of $Λ$ hyperons and their antiparticles is calculated in a 3+1 dimensional viscous hydrodynamic model with initial state from UrQMD hadron/string cascade. We find that, along with recent results from STAR, the mean polarization at fixed centrality decreases as a function of collision energy from 1.5% at $\sqrt{s_{\rm NN}}=7.7$ GeV to 0.2% at $\sqrt{s_{\rm NN}}=200$ GeV. We explore the effects which lead to such collision energy dependence, feed-down corrections and a difference between $Λ$ and $\barΛ$.
The specific shear viscosity (eta/s)_QGP of quark-gluon plasma (QGP) can be extracted from elliptic flow data in heavy-ion collisions by comparing them with the dynamical model VISHNU which couples a viscous fluid dynamic description of the QGP with a microscopic kinetic description of the late hadronic rescattering and freeze-out stage. A robust method for fixing (eta/s)_QGP from the collision centrality dependence of the eccentricity-scaled charged hadron elliptic flow is presented. The systematic uncertainties associated with this extraction method are discussed, with specific attention to …
Possible phase transition of strongly interacting matter from hadron to a quark-gluon plasma state have in the past received c onsiderable interest. It has been suggested that this problem might be treated by percolation theory. The clustering of color sources with percolation (CSPM) is used to determine the equation of state (EOS) and the transport coefficient of the Quark-Gl uon Plasma (QGP) produced in central A-A collisions at RHIC and LHC energies.
We study the stochastic dynamics of c and b quarks in the hot plasma produced in nucleus-nucleus collisions at RHIC and LHC, providing results for the nuclear modification factor R_AA and the elliptic flow coefficient v_2 of the single-electron spectra arising from their semi-leptonic decays. The initial QQbar pairs are generated using the POWHEG code, implementing pQCD at NLO. For the propagation in the plasma we develop a relativistic Langevin equation (solved in a medium described by hydrodynamics) whose transport coefficients are evaluated through a first-principle calculation. Finally, at…
When heavy ions with high energy collide, a hot and dense matter is produced. As the matter expands, the matter undergoes cross-over phase transition from partonic matter to hadronic matter. Jets are created by high pT partons in the early phase of the collisions. Leptons and photons can penetrate the matter without strong interaction. For that reason, jets, leptons and photons are good probes to study the partonic matter in the early phase of the collisions. We report about two probes associated with photon and their results for PHENIX.
The relativistic heavy ion collider (RHIC) was constructed to achieve an asymptotic state of nuclear matter in heavy ion collisions, a near-ideal gas of deconfined quarks and gluons denoted quark-gluon plasma or QGP. RHIC collisions are indeed very different from the hadronic processes observed at the Bevalac and AGS, but high-energy elementary-collision mechanisms are also non-hadronic. The two-component model (TCM) combines measured properties of elementary collisions with the Glauber eikonal model to provide an alternative asymptotic limit for A-A collisions. RHIC data have been interpreted…
Potential near- and long-term physics opportunities with jets, heavy flavors and electromagnetic probes at the Relativistic Heavy Ion Collider (RHIC) are presented. Much new physics remains to be unveiled using these probes, due to their sensitivity to the initial high density stage of RHIC collisions, when quark-gluon plasma (QGP) formation is expected. Additional physics will include addressing deconfinement, chiral symmetry restoration, properties of the strongly-coupled QGP and a possible weakly-interacting QGP, color glass condensate in the initial state, and hadronization. To fully reali…
We discuss recent developments in assessing heavy-quark interaction in the Quark-Gluon Plasma (QGP). While induced gluon radiation is expected to be the main energy-loss mechanism for fast-moving quarks, we focus on elastic scattering which prevails toward lower energies, evaluating both perturbative (gluon-exchange) and nonperturbative (resonance formation) interactions in the QGP. The latter are treated within an effective model for D- and B-meson resonances above T_c as motivated by current QCD lattice calculations. Pertinent diffusion and drag constants, following from a Fokker-Planck equa…
The initial temperature $T_{i}$, energy density $\varepsilon_{i}$, and formation time $τ_{i}$ of the initial state of the QGP formed in the heavy ion collisions at RHIC and LHC energies are determined using the data driven Color String Percolation Model (CSPM). Multiparticle production by interacting strings stretched between projectile and target form a spanning cluster at the percolation threshold. The relativistic kinetic theory relation for $η/s$ is evaluated as a function of $\it T$ and the mean free path ($λ_{mfp}$) using data and CSPM. $η/s$($T_{i}$, $λ_{mfp}$) describes the transition …
We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate.
Possible phase transition of strongly interacting matter from hadron to a Quark-Gluon Plasma (QGP) state have in the p ast received considerable interest. It has been suggested that this problem might be treated by percolation theory. Th e Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the QGP produced in central Au-Au collisions at RHIC energies. The bulk thermodynamic quantities- energy density, entropy density and t he sound velocity- are obtained in the framework of CSPM. It is shown that the results are in excellent agreement with the recent latt…
Thermalization and collective flow of charm (c) and bottom (b) quarks in ultra-relativistic heavy-ion collisions are evaluated based on elastic parton rescattering in an expanding quark-gluon plasma (QGP). We show that resonant interactions in a strongly interacting QGP (sQGP), as well as the effects of parton coalescence, can play an essential role in the interpretation of recent data from the Relativistic Heavy-Ion Collider (RHIC), and thus illuminate the nature of the sQGP and its hadronization. Our main assumption, motivated by recent findings in lattice computations of Quantum Chromodynam…
We take the experimental data for transverse momentum spectra of identified charged hadrons in different centrality classes for nucleus-nucleus (A+A) collisions at various Relativistic Heavy-Ion Collider (RHIC) energies measured by the STAR collaboration. We analyse these data in the framework of color string percolation model (CSPM) in order to extract various percolation parameters at different centralities at RHIC energies to study the effect of collision geometry and collision energy. We use these parameters to study the centrality dependent behaviour of initial temperature of the percolat…
Within a covariant parton cascade, we discuss the impact of both finite shear viscosity $η$ and freeze-out dynamics on the elliptic flow generated at RHIC. We find that the enhancement of $η/s$ in the cross-over region of the QGP phase transition cannot be neglected in order to extract the information from the QGP phase. We also point out that the elliptic flow $v_2(p_T)$ for a fluid at $η/s \sim 0.1-0.2$ is consistent with the one needed by quark number scaling drawing a nice consistency between the nearly perfect fluid property of QGP and the coalescence process.
Quarks of heavy flavors are useful tool to study quark-gluon plasma created in heavy-ion collisions. Due to their high mass and early production time, heavy quarks experience the entire evolution of the system created in these collisions. Open heavy flavor meson measurements are sensitive to the energy loss in the QGP, while quarkonia are sensitive to the temperature of the QGP as they dissociate because of Debye-like screening of color charges. This presentation is a summary of the latest heavy flavor studies performed at RHIC. Results from both STAR and PHENIX experiments are presented, comp…
We propose a novel relation between the low-mass enhancement of dielectrons observed at PHENIX and transport coefficients of QGP such as the charge diffusion constant $D$ and the relaxation time $τ_{\rm J}$. We parameterize the transport peak in the spectral function using the second-order relativistic dissipative hydrodynamics by Israel and Stewart. Combining the spectral function and the full (3+1)-dimensional hydrodynamical evolution with the lattice EoS, theoretical dielectron spectra and the experimental data are compared. Detailed analysis suggests that the low-mass dilepton enhancement …
A major goal of experiments in heavy-ion physics is the characterization of the quark gluon plasma (QGP) produced in the collision of heavy ions at high energy. Direct photons are a particularly good probe of the produced medium because they do not interact strongly and so can escape the medium unmodified, carrying information about when the photon was produced. It is expected that direct photon contributions from different sources (QGP radiation, hard scattering, hadron gas radiation) dominate at different transverse momentum ranges. Low momentum direct photons are dominated by thermal radiat…
We study the production of bottomonium states in heavy-ion reactions at collider energies available at RHIC and LHC. We employ an earlier constructed rate equation approach which accounts for both suppression and regeneration mechanisms in the quark-gluon plasma (QGP) and hadronization phases of the evolving thermal medium. Our previous predictions utilizing two limiting cases of strong and weak bottomonium binding in the QGP are updated by (i) checking the compatibility of the pertinent spectral functions with lattice-QCD results for euclidean correlators, (ii) adapting the initial conditions…
sPHENIX is a new collaboration and future detector project at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). It seeks to answer fundamental questions on the nature of the quark gluon plasma (QGP), including its temperature dependence and coupling strength, by using a suite of precision jet and upsilon measurements that probe different length scales of the QGP. This will be achieved with large acceptance, $|η| < 1$ and $0$-$2π$ in $ϕ$, electromagentic and hadronic calorimeters and precision tracking enabled by a $1.5$ T superconducting magnet. With the increased lumino…
At the Relativistic Heavy Ion Collider (RHIC) collisions of heavy ions at nucleon-nucleon energies of 200 GeV appear to have created a new form of matter thought to be a deconfined state of the partons that ordinarily are bound in nucleons.We discuss the evidence that a thermalized partonic medium, usually called a Quark Gluon Plasma (QGP), has been produced. Then we discuss the effect of this high-density medium on the production of jets and their pair correlations. Next we look at direct photons as a clean electro-magnetic probe to constrain the initial hard scatterings. Finally we review th…
Recently, transport coefficients viz. shear viscosity, electrical conductivity etc. of strongly interacting matter produced in heavy-ion collisions have drawn considerable interest. We study the normalised electrical conductivity ($σ_{\rm el}$/T) of hot QCD matter as a function of temperature (T) using the Color String Percolation Model (CSPM). We also study the temperature dependence of shear viscosity and its ratio with electrical conductivity for the QCD matter. We compare CSPM estimations with various existing results and lattice Quantum Chromodynamics (lQCD) predictions with (2+1) dynamic…
The J/psi is considered to be among the most important probes for the deconfined quark gluon plasma (QGP) created by relativistic heavy ion collisions. While the J/psi is thought to dissociate in the QGP by Debye color screening, there are competing effects from cold nuclear matter (CNM), feed-downs from excited charmonia (chi_c and psi') and bottom quarks, and regeneration from uncorrelated charm quarks. Measurements that can provide information to disentangle these effects are presented in this paper.
At top RHIC and LHC energies the suppression of high transverse momentum ($p_{\mathrm{T}}$) hadrons provides evidence for partonic energy loss in QGP. We study partonic energy loss in the RHIC Beam Energy Scan (BES) by investigating the centrality dependence of the binary-collision-scaled high-$p_{\mathrm{T}}$ yields. Observing a decrease of the scaled yield in more central collisions is proposed as a possible signature for jet quenching. Even at energies and centralities where this signature is lost a QGP may still be formed since competing phenomena responsible for enhancements may overwhelm…
Nonextensive statistics in a Blast-Wave model (TBW) is implemented to describe the identified hadron production in relativistic p+p and nucleus-nucleus collisions. Incorporating the core and corona components within the TBW formalism allows us to describe simultaneously some of the major observations in hadronic observables at the Relativistic Heavy-Ion Collider (RHIC): the Number of Constituent Quark Scaling (NCQ), the large radial and elliptic flow, the effect of gluon saturation and the suppression of hadron production at high transverse momentum (pT) due to jet quenching. In this formalism…
The presence of thermal gluons reduces the stimulated gluon emission off a heavy quark propagating in the quark-gluon plasma (QGP) while absorption causes reduction of the radiative energy loss. On the other hand, the chromo-electromagnetic field fluctuations present in the QGP lead to collisional energy gain of the heavy quark. The net effect of the thermal gluon absorption and field fluctuations is a reduction of the total energy loss of the heavy quark, prominent at the lower momenta. We consider both kind of the energy gains along with the usual losses, and compute the nuclear modification…
Recent experimental advances at the Relativistic Heavy Ion Collider (RHIC) and the large center-of-mass energies available to the heavy-ion program at the Large Hadron Collider (LHC) will enable strongly interacting matter at high temperatures and densities, that is, the quark-gluon plasma (QGP), to be probed in unprecedented ways. Among these exciting new probes are fully-reconstructed inclusive jets and the away-side hadron showers associated with a weakly or electromagnetically interacting boson, or, tagged jets. Full jet reconstruction provides an experimental window into the mechanisms of…
Properties of bottomonia (Upsilon, chi_b and Upsilon') in the Quark-Gluon Plasma (QGP) are investigated by assessing inelastic reaction rates and their interplay with open-bottom states (b-quarks or B-mesons) and color-screening. The latter leads to vanishing quarkonium binding energies at sufficiently high temperatures (close to the dissolution point), which, in particular, renders standard gluo-dissociation, g+Upsilon -> b + b-bar, inefficient due to a substantial reduction in final-state phase space. This problem is overcome by invoking a "quasifree" destruction mechanism, g,q,q-bar + Upsil…
We study the emission characteristics of thermal photons at RHIC and LHC as affected by both the space-time evolution of the bulk medium and the thermal emission rates. For the former we compare the results of two evolution models (expanding fireball and hydrodynamics). For the latter, we detail the influence of hadronic emission components and study a speculative scenario by upscaling the default QGP and hadronic rates around the pseudo-critical region.
We summarize the di-hadron correlation results from RHIC, focusing on the high $p_T$ region and lower $p_T$ region for the away-side. The former is consistent with fragmentation of jets that surviving the medium, while the latter suggests the redistribution of the energy from the quenched jets. We also discuss the role of the jet in the intermediate $p_T$.
With the new viscous hydrodynamic + hadron cascade hybrid code VISHNU, a rather precise (O(25%)) extraction of the QGP shear viscosity (eta/s)_QGP from heavy-ion elliptic flow data is possible if the initial eccentricity of the collision fireball is known with <5% accuracy. At this point, eccentricities from initial state models differ by up to 20%, leading to an O(100%) uncertainty for (eta/s)_QGP. It is shown that a simultaneous comparison of elliptic and triangular flow, v_2 and v_3, puts strong constraints on initial state models and can largely eliminate the present uncertainty in (eta/s)…
Massachusetts Institute of Technology（麻省理工学院）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Brookhaven National Laboratory（布鲁克海文国家实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
The study of correlations and fluctuations can provide evidence for the production of the quark-gluon plasma (QGP) in relativistic heavy ion collisions. Various theories predict that the production of a QGP phase in relativistic heavy ion collisions could produce significant event-by-event correlations and fluctuations in, transverse momentum, multiplicity, etc. Some of the recent results using STAR at RHIC will be presented along with results from other experiments at RHIC. The focus is on forward-backward multiplicity correlations, balance function, charge and transverse momentum fluctuation…
Over the past 15 years, an extensive program of high energy nuclear collisions at BNL and CERN has been devoted to the experimental search for the quark-gluon plasma predicted by QCD. The start of RHIC this year will increase the highest available collision energy by a factor 10. This seems a good time for a critical assessment: what have we learned so far and what can we hope to learn in the coming years?
We calculate the elliptic flow of thermal photons from Au+Au collisions at RHIC energies for a range of values for the formation time $τ_0$ but fixed entropy (or particle rapidity density). The results are found to be quite sensitive to $τ_0$. The $v_2$ for photons decreases as $τ_0$ decreases and admits a larger contribution from the QGP phase which has a smaller $v_2$. The elliptic flow coefficient for hadrons, on the other hand, is only marginally dependent on $τ_0$.
Direct photon production in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV has been measured. The result is compared to several theoretical calculations, and found that it is not inconsistent with ones including thermal radiation from QGP or jet-photon conversion process on top of a NLO pQCD expectation. The direct photon contribution in dilepton measurement is also evaluated.
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.
Quark-Gluon Plasma (QGP), a QCD state of matter created in ultra-relativistic heavy-ion collisions, has remarkable properties, including, for example, a low shear viscosity over entropy ratio. By detecting the collection of low-momentum particles that arise from the collision, it is possible to gain quantitative insight into the created matter. However, its fast evolution and thermalization properties remain elusive. Only using high momentum objects as probes of QGP can unveil its constituents at different wavelengths. In this review, we attempt to provide a comprehensive picture of what was, …
The Relativistic Heavy Ion Collider (RHIC) studies nuclear matter under a variety of conditions. Cold nuclear matter is probed with deuteron-gold collisions, while hot nuclear matter(possibly a quark-gluon plasma (QGP)) is created in heavy-ion collisions. The distribution of spin in polarized nucleons is measured with polarized proton collisions, and photoproduction is studied using the photons that accompany heavy nuclei. The deuteron-gold data shows less forward particle production than would be expected from a superposition of $pp$ collisions, as expected due to saturation/shadowing. Partic…
We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au+Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, e…
We analyze high multiplicity proton-proton ($pp$) collision data in the framework of the String Percolation Model (SPM) that has been successful in describing several phenomena of multiparticle production, including the signatures of recent discovery of strongly interacting partonic matter, the Quark Gluon Plasma (QGP), in relativistic heavy-ion collisions. Our study in terms of the ratio of shear viscosity and entropy density ($η/s$) and the (LQCD) predicted signature of QCD change of phase, in terms of effective number of degrees of freedom ($ε/T^4$), reiterates the possibility of strongly i…
In this paper we show azimuthal particle correlations in three different small-system collisions with different intrinsic initial geometries. The simultaneous constraints of $v_2$ and $v_3$ in $p/d/^3$He$+$Au collisions definitively demonstrate that the $v_n$'s are correlated to the initial geometry. In addition, we find that hydrodynamical models which include QGP formation describe simultaneouly the elliptic and triangular flow data in a statistically acceptable manner in all three systems.
At the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, heavy nuclei are collided at high energies to create matter that is hot enough and dense enough to dissolve hadrons into a quark-gluon-plasma (QGP). In this lecture, dedicated to the memory of Aditya Sambamurti, I present an introduction to heavy-ion collisions and highlights from the first decade of RHIC results.
Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor ($R_\text{AA}$), directed flow ($v_1$) and elliptic flow ($v_2$) coefficients of heavy mesons and their decayed electrons at the RHIC energy. We find that the counter-clockwise tilt of the nuclear matter in the reaction plane results in a positive (negative) heavy flavor $v_1$ in the ba…
High-energy heavy-ion collisions generate extremely strong magnetic field which plays a key role in a number of novel quantum phenomena in quark-gluon plasma (QGP), such as the chiral magnetic effect (CME). However, due to the complexity in theoretical modellings of the coupled electromagnetic fields and the QGP system, especially in the pre-equilibrium stages, the lifetime of the magnetic field in the QGP medium remains undetermined. We establish, for the first time, a kinetic framework to study the dynamical decay of the magnetic field in the early stages of a weakly coupled QGP by solving t…
The study of heavy flavor production in relativistic heavy ion collisions is an extreme experimental challenge but provides important information on the properties of the Quark-Gluon Plasma (QGP) created in Au+Au collisions at RHIC. Heavy-quarks are believed to be produced in the initial stages of the collision, and are essential on the understanding of parton energy loss in the dense medium created in such environment. Moreover, heavy-quarks can help to investigate fundamental properties of QCD in elementary p+p collisions. In this work we review recent results on heavy flavor production and …
Direct photons have been proposed as a promising signature for the quark-gluon plasma (QGP) formation in relativistic heavy-ion collisions. Recently WA98 presented the first data on direct photons in Pb+Pb-collisions at SPS. At the same time RHIC started with its experimental program. The discovery of the QGP in these experiments relies on a comparison of data with theoretical predictions for QGP signals. In the case of direct photons new results for the production rates of thermal photons from the QGP and a hot hadron gas as well as for prompt photons from initial hard parton scatterings have…
Heavy flavor production is an ideal tool to study the properties of the Quark Gluon Plasma (QGP). The heavy flavor production at the Relativistic Heavy Ion Collider (RHIC) has its unique kinematic coverage and different production mechanisms from the Larger Hadron Collider (LHC) measurements. Heavy flavor products created in heavy ion collisions experience the whole evolution of nuclear medium. It's critical to measure both open and closed heavy flavor products in different collision systems to isolate cold/hot nuclear medium effects and initial/final state interactions. We report recent heavy…
Measurements of $π^0$, identified charged hadrons, direct-single-$γ$, direct single-$e^{\pm}$ and jets are expected to be important probes of the Quark Gluon Plasma (QGP) at LHC as they are at RHIC. Recent results from RHIC will be presented, with implications, possibly grave, for LHC. Issues of soft-physics, such as $E_T$ distributions, will be discussed with questions as to: whether the soft multipicity or sum-transverse energy ($E_T$), may be the only quantity at LHC to exhibit number of collision scaling? or whether the anisotropic flow ($v_2$) will exceed the hydrodynamic limit?
Isothermal compressibility ($κ_{\rm T}$) is an important thermodynamic observable which gives information about the deviation of a system from perfect fluid behavior. In this work, for the first time we have estimated the isothermal compressibility of QCD matter formed in high energy hadronic and nuclear collisions using color string percolation model (CSPM), where we investigate the change in $κ_{\rm T}$ as a function of final state charged particle multiplicity and initial percolation temperature across various collision species. The estimated initial percolation temperature for different co…
A brief overview of direct-photon measurements in p+p and Au+Au collisions at sqrt(s_NN) = 200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is given. Direct-photon yields for pT > 4 GeV/c and photon-hadron azimuthal correlations were determined with the aid of an electromagnetic calorimeter. By detecting e+e- pairs from the internal conversion of virtual photons direct-photon yields were measured between 1 < pT < 4 GeV/c. In Au+Au collisions thermal photons from a quark-gluon plasma (QGP) are expected to contribute significantly to the total direct-photon yield …
At RHIC, a suppression, $R_{AA}\approx 0.2$ relative to binary-scaling, for $π^0$ with $5\leq p_T\leq 20$ GeV/c was discovered in central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV, and surprisingly also for single-electrons from the decay of heavy quarks. Both these results have been confirmed in Pb+Pb collisions at the LHC at $\sqrt{s_{NN}}=2.76$ TeV. In this $p_T$ range, the LHC results for pions nearly overlap the RHIC results but the flatter spectrum at LHC implies that the energy loss in the medium must be $\sim 40$% larger than at RHIC. At LHC, the unique and beautiful measurement of t…
