International Journal of Modern Physics E

We briefly describe two statistical hadronization models, based respectively on the presence and absence of light quark chemical equilibrium, used to analyze particle yields in heavy ion collisions. We then try to distinguish between these models using K/π fluctuations data. We find that while the non-equilibrium model provides an acceptable description of fluctuations at top SPS and RHIC energies, both models considerably under-estimate fluctuations at low SPS energies.

Similarities between cosmological scenarios on the Universe evolution after “Big Bang” and the behavior of the highly excited nuclear matter formed in relativistic nuclear collisions, immediately after collisions, are considered to do an estimation of a “microscopic Hubble parameter/constant” for the expansion rate in relativistic nuclear collisions, similar with the cosmological Hubble constant. Temporal connections between the evolution of the nuclear matter after impact and the scenarios on the Universe evolution after “Big Bang” are introduced. Experimental results on participants, fireball sizes (identical particle interferometry), densities, particle spectra and temperatures have been used. A “Hubble scale” for temporal evolution can be obtained. Satisfactory agreement with Buda-Lund model estimations has been obtained.

The STAR experiment at RHIC has measured identified π^±, K^± and spectra and ratios from and 200 GeV Cu+Cu collisions. The new Cu+Cu results are studied with hydro-motivated blast-wave and statistical model frameworks in order to characterize the freeze-out properties of this system. Along with measurements from Au+Au and p+p collisions, the obtained freeze-out parameters are discussed as a function of collision energy, system size, centrality and inferred energy density. This multi-dimensional systematic study reveals the importance of the collision geometry and furthers our understanding of the QCD phases.

Elliptic flow is easy to compute in hydrodynamics. However experimentally it is obtained in an indirect way. The question we address in this paper (using the hydrodynamical code NeXSPheRIO) is how comparable are these two approaches. We find that there is a disagreement between both methods of 15–30% for η = 0 and 30% for p⊥ = 0.5 GeV.

Nuclear stopping has been measured at a range of different energies in heavy ion experiments. In this contribution proton data from the BRAHMS experiment at RHIC running at are presented. Furthermore data from AGS, SPS and RHIC are used to estimate the stopping, energy loss and multiplicity at LHC.

The pixel detector of CMS can be used to reconstruct very low p_T charged particles down to about 0.1 GeV/c. This can be achieved with high efficiency, good resolution and a negligible fake rate for elementary collisions. In the case of central PbPb collisions the fake rate can be kept low for p_T > 0.4 GeV/c. In addition, the detector can be employed for identification of neutral hadrons (V0s) and converted photons.

We study degree of coherence of pion sources by making use of two- and three-particle momentum intensity correlation functions in S+Pb, Pb+Pb, and Au+Au collisions at SPS and RHIC. For each system, we calculate a chaotic fraction ε and the number of coherent sources α from the chaoticity λ of the two-pion correlation function and the weight factor ω of the three-pion correlator. We take account of long-lived resonance decay contribution to the λ factor by making a correction with the help of a statistical model. The result gives strong constraints on the source and shows roughly increasing number of coherent sources as multiplicity increases.

We use a model of quark-gluon plasma granular droplets that evolve hydrodynamically to investigate pion elliptic flow and Hanbury–Brown–Twiss interferometry. We find that the data of pion transverse momentum spectra, elliptic flows, and HBT radii in Au + Au collisions at RHIC can be described well by an expanding source of granular droplets with an anisotropic velocity distribution.

We present the STAR preliminary results of inclusive photon v₂ as a function of p_T in AU+AU collisions. Photons are identified in the STAR Barrel Electromagnetic Calorimeter (BEMC). Non-flow effects are suppressed by obtaining the event plane in different pseudo-rapidity regions. The v₂ of π⁰ decay products is calculated from the known v₂ and spectra of hadrons and is compared to the inclusive photon v₂. The comparison indicates that direct photon v₂ is small.

The energy and system size dependence of pseudorapidity (η) and multiplicity distributions of photons are measured in the region −2.3 ≤ η ≤ −3.7 for Cu + Cu collisions at and 62.4 GeV. Photon multiplicity measurements at forward rapidity have been carried out using a Photon Multiplicity Detector (PMD) in the STAR experiment. Photons are found to follow longitudinal scaling for Cu + Cu collisions for 0–10% centrality. A Comparison of pseudorapidity distributions with HIIJING model is also presented.

We have performed the first measurement of elliptic flow (v₂) fluctuations in nucleus-nucleus collisions. In this paper, we describe the analysis method we have developed for this measurement. In this method, v₂ is determined event-by-event by a maximum likelihood fit. The non-statistical fluctuations are determined by unfolding the contribution of statistical fluctuations and detector effects using Monte Carlo simulations. Application of this method to measure dynamical fluctuations in events from a different Monte Carlo event generator is presented.

Multiparticle production at high energies is described in terms of color strings stretched between the projectile and target. As the string density increases, overlap in the transverse plane leads to cluster formation. At some critical density a macroscopic cluster appears, spanning the entire system. This marks the percolation phase transition. Data from p+p, d+Au and Au+Au collisions at RHIC has been analyzed using the STAR detector to obtain the percolation density parameter, η. The particle p_T spectrum from 200 GeV p+p data is parametrized using a power law. Values of the fit parameters are used in the d+Au and Au+Au analysis. For 200 GeV Au+Au collisions, the value of η is found to lie above the critical percolation threshold, while for other collision systems and energies, it is below the critical value. This supports the idea of string percolation, which at high enough string density is a possible mechanism to explore the hadronic phase transition to a quark-gluon plasma.

The PHENIX experiment at RHIC measured ω, η and -meson production at high p_T in p + p, d + Au and Au + Au collisions at . Measurements performed in different hadronic decay channels give consistent results. The measured ratios of all three mesons to π⁰ are found to be flat as a function of p_T in p + p collisions and equal to ω/π⁰ = 0.81 ± 0.02 ± 0.07, η/π⁰ = 0.48 ± 0.02 ± 0.02 and . Nuclear modification factor measured for ω-mesons in central Au+Au collisions is R_AA = 0.4 ± 0.15.

The directed flow v₁, elliptic flow v₂ and the fourth order anisotropic flow v₄ of Ω, p, K and π have been studied in the framework a parton cascade model, namely A Multi-Phase Transport (AMPT) model for ¹⁹⁷Au + ¹⁹⁷Au collisions at . Transverse momentum (p_T) dependence of v₂ and v₄ and rapidity dependence of v₁ are presented. The results show that the v₂ of Ω obeys the constituent quark number scaling which has been observed for other mesons and baryons. It is seen that is scaled better by 1.2 than 0.5. The comparisons of Ω elliptic flow v₂ among the default version of AMPT, the melting version of AMPT and RQMD model calculation shows that parton scattering process is important to reproduce the sizeable v₂, and the string melting AMPT model preferably reproduces Ω elliptic flow v₂.

We investigate the effect of chemical freeze-out on identified particle spectra at 200 A GeV Au-Au Collisions at RHIC, by utilizing a full three-dimensional hydrodynamical calculation. The hydrodynamical code SPheRIO we employed is based on the smoothed particle hydrodynamic algorithm. In order to describe the spectra of strange hadrons, the code has been further improved by explicitly incorporating the strangeness conservation and a chemical freeze-out mechanism. In our model, strange hadrons such as Λ, Ξ, Ω and φ undergo the chemical freeze-out immediately after the hadronization, and their multiplicities are fixed thereafter. At a lower temperature the thermal freeze-out takes place for all the particles. It is shown that the present model provides a reasonably good description for the spectra of identified particles, in particular, considerable improvement is observed for those of strange hadrons.

The influence of Bose–Einstein statistics on multi-particle production characterized for various systems and energies by the STAR collaboration provides interesting information about the space-time dynamics of relativistic heavy-ion collisions at RHIC. We present the centrality and transverse mass dependence measurements of the two-pion interferometry in Au+Au collisions at and Cu+Cu collisions at and 200 GeV. We compare the new data with previous STAR measurements from p+p, d+Au and Au+Au collisions at . In all systems and centralities, HBT radii decrease with transverse mass in a similar manner, which is qualitatively consistent with collective flow. The scaling of the apparent freeze-out volume with the number of participants and charged particle multiplicity is studied. Measurements of Au+Au collisions at same centralities and different energies yield different freeze-out volumes, which mean that N_part is not a suitable scaling variable. The multiplicity scaling of the measured HBT radii is found to be independent of colliding system and collision energy.

The freeze out of the expanding systems, created in relativistic heavy ion collisions, will be discussed. We combine kinetic freeze out equations with Bjorken type system expansion into a unified model. Such a model is a more physical generalization of the earlier simplified non-expanding freeze out models. We shall see that the basic freeze out features, pointed out in the earlier works, are not smeared out by the expansion.

We present preliminary results for Cu+Cu collisions at at the BRAHMS experiment from charged hadron spectra and nuclear modification factors as a function of centrality and pseudo-rapidity. Deviations from binary scaling at intermediate and high-p_T reveal themselves as a suppression in the transverse momentum distribution of produced particles. The observed suppression depends on the volume of the interaction region through which produced hadrons have to travel. While there is still significant suppression, R_cp seems to depend very little on pseudo-rapidity.

In this analysis we measure the azimuthal angle (φ) dependence of hadrons with respect to the reaction plane (Ψ_RP) in events that were triggered by a high-p_T π⁰ of 5-10 GeV. Fitting the distribution of hadrons with a function of the type ξ(1 + 2v₂cos (2(φ − Ψ_RP))), we observe that there is no significant statistical difference between v₂ inclusive hadrons and those hadrons from hard scattering events. We also compare the near-side jet widths using PYTHIA simulations with h^±−h^± correlations in Au+Au at .

A parton and hadron cascade model, PACIAE, is applied to follow the particle transport in both the partonic and hadronic stages of the 0–5% most central Au+Au collisions at . We have determined the specific heat of π⁺ + π⁻ in pure hadronic scenario (hadonic final state) and the specific heat of in pure partonic scenario (partonic initial state). The specific heat of π⁺ + π⁻ in hadronic scenario is nearly a factor of 1.2 smaller than that of in partonic scenario. However, the specific heat of is very hard to survive the hadronization.

Specific heat capacities of π meson and different quarks after parton cascade AMPT model in Au+Au collisions at have been tentatively extracted from the event-by-event temperature fluctuations in the region of low transverse mass. The specific heat capacity of π meson shows a slight dropping trend with increasing impact parameter. The specific heat capacities of different quarks increase with the mass of quark, and the sum of up and down quark's specific heat capacities was found to be approximately equal to that of π meson.

At the Relativistic Heavy Ion Collider (RHIC) elliptic flow signals (v₂) appear to be stronger than those measured at lower center-of-mass energies. With the beginning of heavy ion beams at the Large Hadron Collider (LHC) it is important to have a reliable tool for simulating v₂ at the LHC Pb–Pb center-of-mass energy of 5.5 A TeV. In this work we used the heavy ion simulation tool HYDJET to study elliptic flow at the event generator level. The generator level elliptic flow v₂ for Pb–Pb collisions was two-particle and four-particle cumulants.

In this work we compare the nuclear modification factors in proton (deuteron) — nucleus collisions at CERN SPS, FNAL and RHIC energies in a wide p_T range. In these experiments the nuclear modification factor has shown an enhancement at p_T ≈ 4 GeV/c. The height of this “Cronin peak” depends on the c.m. energy of the collision, as it is subject to stronger shadowing at higher energies. One of the aims of this contribution is to analyze the shadowing phenomenon at lower (2 GeV/c ≲ p_T ≲ 4 GeV/c) and intermediate (4 GeV/c ≲ p_T ≲ 8 GeV/c) transverse momentum. Different shadowing parametrizations are considered and the obtained Cronin peaks are investigated at RHIC and LHC energies.

A gluon or quark jet traversing through a quark-gluon plasma can be converted into a quark or gluon jet through scatterings with thermal partons. Their conversion rates due to two-body elastic and inelastic scattering as well as scatterings involving gluon radiation are evaluated in the lowest order in Quantum Chromodynamics (QCD). Including both energy loss and conversions of quark and gluon jets in the expanding quark-gluon plasma produced in relativistic heavy ion collisions, we find a net conversion of quark jets to gluon jets. This reduces the difference between the nuclear modification factors for quark and gluon jets in central heavy ion collisions and thus enhances the p/π⁺ and ratios at high transverse momentum. Using the larger QCD coupling constant from lattice QCD calculations than that given by the perturbative QCD further enhances the net quark to gluon jet conversion rate, leading to a closer similarity between these ratios at high transverse momentum in central Au+Au collisions at and in p+p collisions at same energy as observed in experiments.

Large transverse momentum jets provide unique tools to study dense QCD matter in high-energy heavy-ion collisions. Results from RHIC on suppression of high transverse momentum particles in Au+Au collisions indicate a significant energy loss of leading partons in the dense and strongly interacting matter formed in these collisions. The LHC will collide Pb ions at , where the cross section of hard scattering will increase dramatically. Large production rates, the large acceptance of the CMS calorimeters and tracking system, combined with the capability of triggering on jets, will extend the transverse momentum reach of charged particle spectra and nuclear modification factors up to p_T > 200 GeV/c.

We present the transverse momentum spectra for charged hadrons as well as for identified particles produced in Au + Au and p + p collisions at for different event centralities (minimum bias spectra for p + p) in narrow rapidity ranges (±0.1), for midrapidity and high rapidities (up to 3.8). Nuclear modification factor R_AA for identified baryons and mesons, as well as for inclusive charged hadrons, at rapidities from 0 to 3.8 will be shown and discussed.

An important tool in quark-gluon plasma studies at RHIC has been the measurement of dijets investigated via leading hadron correlations. With much higher rates for hard processes at the Large Hadron Collider, studies of Z⁰-tagged jets become possible. A clear experimental signature is provided by the measurement of muon pairs from the Z⁰ decays, for which CMS is an ideally suited detector. Instead of measuring back-to-back correlations of two strongly interacting particles, one side is replaced by an electromagnetic probe which propagates through the plasma undisturbed and provides a measurement of the energy of the initial hard scattering. We propose to use lepton-pair tagged jets to study medium-induced partonic energy loss and to measure in-medium parton fragmentation functions. The lepton pairs from semileptonic decays of heavy meson pairs ( and ) are a background source for the tagged dilepton-jet signal. We present the calculated signal rates (using PYTHIA) and background rates (using HVQMNR). We also discuss strategies for maximizing the signal-to-background ratio.

A vigorous debate has recently concerned the quenching of jets by the expanding hot and dense medium created in high-energy nuclear collisions accompanied by Mach-cone-like structures at STAR and PHENIX.^1,2 Large angle (w.r.t. the jet axis) peaks in the angular distribution of the particles created in the jet show up in both, 2- and 3-particle correlations. It is assumed that this reflects the interaction of the jet with the medium.^3,4 However, the jet interactions with the medium are theoretically not understood well enough. Therefore, we present a first ideal (3+1)dimensional hydrodynamics approach with a sudden jet-energy deposition. Clearly, the hydrodynamical evolution strongly depends on the underlying equation of state (EoS) of the medium and therefore the influcence of the EoS on the evolution of the jet through the medium is of great interest for probing the EoS, the nature of the phase transition.

We present a method based on three-particle azimuthal correlation cumulants for the study of the interaction of jets with the medium produced in heavy ion collisions at RHIC and LHC where jets cannot be reconstructed on an event-by-event basis with conventional jet finding algorithms. The method is specifically designed to distinguish a range of jet interaction mechanisms such as Mach cone emission, gluon Cerenkov emission, jet scattering, and jet broadening. We discuss how anisotropic flow background conti-butions of second order (e.g. ) are suppressed in three-particle azimuthal correlation cumulants, and discussed specific model representations of di-jets, away-side scattering, and Mach cone emission.

The yield of charged hadrons at intermediate p_T (2-5 GeV/c) on the away-side of a high p_T hadron trigger is known to be suppressed in central relativistic heavy-ion collisions. The mechanism by which the jet opposite the trigger has its redistributed is not yet fully understood. Although rarer than dijets, direct photon-jet pairs may provide additional constraints on parton energy loss models. The benefits of direct photon triggers are two-fold. In contrast to dijet systems where the jet energy is known only after full jet reconstruction, the direct photon carries approximately the full energy of the jet. Also, the trigger photons do not suffer from the same geometrical bias that causes high p_T hadrons from jets to be produced predominately near the surface of the collision region. This poster discusses the method by which the direct photon correlation signal can be separated from the decay photon correlation signal. We present the results of two particle correlation studies of charged hadrons associated with high p_T photon triggers in p−p collisions. The results are compared to data from Au−Au collisions and expectations from the PYTHIA event generator.

In non-central high energy heavy ion collisions, the initial spatial anisotropy is transferred to the final momentum anisotropy due to a pressure gradient in the collision participants. We present the p_T and centrality dependence of the azimuthal anisotropy for charged hadrons in different energies and collision systems measured by the PHENIX experiment at RHIC. The relation of initial geometrical eccentricity to the azimuthal anisotropy will also be discussed.

Recent experimental investigations have focussed on the abnormal spatial distribution of away side jet fragments as signals of significant medium induced effects. A variety of theoretical models including recent string-theory based efforts have supported the notion of Mach Cone like effects in the low viscosity QGP fluid. However, the presence of significant flow fields may deflect the fragmentation direction producing a significantly differing type of jet topology from that of the Mach cone. Three particle correlation functions constitute a powerful method whereby the predominance of one or the other type of mechanism can be differentiated. In this work the use of such an approach will be demonstrated via simulations and the results of its application to RHIC data will be presented.

Two-particle azimuthal correlations have allowed detailed study of the modification to di-jets in the hot, dense medium created in RHIC collisions. Light can be shed by such correlations on many novel effects discovered at RHIC such as the enhanced p/π⁺ ratio and conical structure of events with energy loss. Using π⁰ triggers to reduce the effect of recombination we utilize high-p_T correlations to explore the away-side structure.

An important ingredient for studying non-equilibrium evolution of partons at RHIC and LHC is to have physical initial conditions for the partonic system. In this paper we investigate the initial conditions with chemical non-equilibrium at RHIC. Considering the parton production, we studied evolution of the partonic medium with chemical non-equilibrium toward a fully equilibrated partonic system. By using a set of rate equations which describe the chemical equilibration of gluons and quarks, and putting different initial conditions, we obtained the transverse energy production dE_T/dy and particle multiplicities dN/dy. Comparing the experimental data of dE_T/dy and dN/dy with numerical results, we get following initial conditions for the formation of partonic system: the initial temperature is around 550 MeV and the initial fugacity λ_g is from 0.4 to 0.75. It is shown that, until the partonic medium freezes out the partonic system hasn't been totally chemical equilibrated.

We present the results of the two-particle Δφ correlation between high p_T π⁰ and charged hadrons in Cu+Cu collisions at . Clear away-side jet signals are seen in central Cu+Cu collisions at all associated hadron p_T, albeit suppressed by factor of 2 above 2 GeV/c. This level is similar to the suppression seen for inclusive hadrons at high p_T (> 7 GeV/c). However, this agreement is argued to be the result of a cancellation between a flatter away-side parton spectra due to the requirement of high p_T triggers and a bigger energy loss due to a longer path length traversed by the away-side jet.

We present results from STAR on 3-particle azimuthal correlations for a 3 < p_T < 4 GeV/c trigger particle with two softer 1 ≤ p_T ≤ 2 GeV/c particles. Results are shown for pp, d+Au and high statistics Au+Au collisions at . We observe a 3-particle correlation in central Au+Au collisions which may indicate the presence of conical emission. In addition, the dependence of the observed signal angular position on the p_T of the associated particles can be used to distinguish conical flow from simple QCD-Čerenkov radiation. An important aspect of the analysis is the subtraction of combinatorial backgrounds. Systematic uncertainties due to this subtraction and the flow harmonics v₂ and v₄ are investigated in detail.

Hard-scattering of point-like constituents (or partons) in p-p collisions was discovered at the CERN-ISR¹ in 1972 by measurements utilizing inclusive single or pairs of hadrons with large transverse momentum (p_T). Due to the steeply falling power-law p_T spectrum of the hard-scattered partons, the inclusive single particle (e.g. π⁰) p_Tt spectrum from parton fragmentation to a jet is dominated by trigger fragments with large z_t ~ 0.7–0.8, where z_t = p_Tt/p_Tjet is the fragmentation variable. It was generally assumed, following Feynman, Field and Fox,² as shown by data from the CERN-ISR experiments, that the p_Ta distribution of away side hadrons from a single particle trigger [with p_Tt], corrected for z_t, would be the same as that from a jet-trigger and follow the same fragmentation function as observed in e⁺e⁻ or DIS. PHENIX³ attempted to measure the fragmentation function from the away side x_E ~ P_Ta/p_Tt distribution of charged particles triggered by a π⁰ in p−p collisions at RHIC and showed by explicit calculation that the x_E distribution is actually quite insensitive to the fragmentation function. Illustrations of the original arguments and ISR results will be presented. Then the lack of sensitivity to the fragmentation function will be explained, and an analytic formula for the x_E distribution given, in terms of incomplete Gamma functions, for the case where the fragmentation function is exponential. The away-side distribution in this formulation has the nice property that it both exhibits x_E scaling and is directly sensitive to the ratio of the away jet to that of the trigger jet, , and thus can be used, for example, to measure the relative energy loss of the two jets from a hard-scattering which escape from the medium in A+A collisions. Comparisons of the analytical formula to RHIC measurements will be presented, including data from STAR^4,5 and PHENIX,^3,6 leading to some interesting conclusions.

We present a systematic analysis of azimuthal correlations between inclusive photons detected in the STAR Barrel Electromagnetic Calorimeter and tracks measured in the Time Projection Chamber in p+p and d+Au collisions. These measurements provide insight in basic properties of jet fragmentation in p+p and d+Au collisions at RHIC energies and also serve as a reference for medium-modified fragmentation in nuclear collisions. The on-line trigger on high-p_T photons in the Barrel Calorimeter provides a substantial sample of triggered events with photons at high-p_T. Even at this p_T, the photon sample is dominated by π₀ decays, allowing to explore jet fragmentation with a leading π₀ in detail.

Strong di-jet correlations have been observed in p+p and d+Au collisions at . It is important to study how this jet-correlation is affected by the hot, dense medium produced in heavy-ion collisions at RHIC. In this contribution we will study the two particle correlation and probe how the di-jet shape evolves as a function of centrality in Cu+Cu collisions comparing to p+p, specifically using the near-side width and p_Tout. We will use high p_T reconstructed π⁰ as our identified trigger in tagging jets.

It has been observed a “Mach-like” structure of di-hadron azimuthal correlations in Au + Au central collisions at in the framework of a multi-phase transport model (AMPT) with both partonic and hadronic interactions. In this paper, we will show centrality, transverse momentum (p_T) and pseudorapidity (η) dependences of “Mach-like” structure. The splitting parameter D, i.e. half distance between two splitting peaks on away side, decreases with the impact parameter b (corresponding to centrality) and slightly increases with transverse momentum of associated hadrons , which from string melting AMPT version is consistent with experimental results. And the splitting parameter D is flat in mid-pseudorapidity region and rapidly decreases with the increasing of high-|η^assoc|.

The measurement of strangeness is a valuable tool for understanding the reaction mechanism of nuclear collisions since all the strange particles need to be created during the reaction. Also, strangeness enhancement is one of the predicted signals of the QGP. In the present work we will discuss the behaviour of the strangeness production (i.e. K/π ratio) with rapidity and baryo-chemical potential in Au+Au collisions at 62.4 A GeV. In this particular reaction, BRAHMS is able to identify particles over 3.5 rapidity units and thereby cover a wide range of ratios, including the fragmentation region. We will show spectra and ratios of identified particles as a function of p_T and rapidity.

The effects of heavy quarks energy loss on the transverse momentum spectra of single muons are studied. The energy loss of heavy quarks when traversing the medium formed in PbPb collisions at is calculated by implementing the collision geometry and the quenching weights. The medium density is assumed to decrease at forward pseudo-rapidity and to be proportional with pseudo-rapidity multiplicity dN/dη. Muons from W decays can be used as a medium-blind reference to quantify the effect of heavy quarks energy loss on the single muon production.

The charm quark thermalization in quark-gluon plasma is described by a transport model in relaxation time approximation. Combining the transport equation for charm quarks with the hydrodynamic description for the medium, we calculated the charm quark transverse momentum distribution and discussed its dependence on the relaxation time.

Transverse momentum spectra of Λ and particles are presented for Cu+Cu at collisions observed at STAR, and compared to Au+Au measurements at the same energy. For both systems, a number of observables are shown to increase at mid-rapidity (|y| < 0.5) with increasing centrality. These are the integrated Λ and yields, the integrated ? and yields per participating nucleon, and mid-p_T(1 GeV/c → 4.5 GeV/c) ratios. The R_CP ratio is found to be higher for the Λ yields at mid-p_T compared to the yields for both the Cu+Cu and Au+Au data. In contrast, when similar numbers of participating nucleons are considered for the Cu+Cu and Au+Au data, an indication of increased bulk strangeness production and a higher mid-p_T(1 GeV/c → 4.5 GeV/c) ratio are found, for Cu+Cu.

J/ψ production is closely related to the production of the strongly interacting Quark-Gluon Plasma (sQGP) in relativistic heavy ion collisions. To study the effects of charm quark dynamics on J/ψ production, the phase space distributions of charm and anti-charm quarks are generated using A Multi-Phase Transport (AMPT) model. These charm quarks then coalesce into J/ψ particles. The production and flow of J/ψ show strong sensitivity to final state charm interactions. The results are compared to charm quark and D meson results from the AMPT model and recent predictions from other models.

J/ψ azimuthal distribution relative to the reaction plane has been studied Pb-Pb collisions at 158 A GeV/c. Different absorption mechanisms are expected to induce J/ψ azimuthal anisotropy at this energy. The present analysis has been performed on the data sample of 100 000 J/ψ's collected in year 2000 by the NA50 Collaboration. The reaction plane is estimated from the azimuthal distribution of the neutral transverse energy measured by the electromagnetic calorimeter. The numbers of J/ψ's in different bins of azimuthal angle relative to the reaction plane as well as the Fourier coefficients and (uncorrected for event plane resolution) are presented in this paper.

A strong suppression of non-photonic electrons in Au+Au collisions is observed at Rhic. This is in disagreement with the expected dominance of the energy loss via gluon radiation, which predicts a much weaker suppression of heavy flavours due to the dead cone effect. However, collisional energy loss is also important, as demonstrated recently by the Soft Colour Interaction Jet Quenching model. Based on this model we show that collisional energy loss of charm quarks gives a suppression of electrons of the observed magnitude, but the contribution from beauty decays, which dominates at intermediate and large p⊥, results in a somewhat weaker overall suppression of electrons than observed.

In this work we calculate the J/ψ production in the initial stage of hadronic and nuclear collisions at RHIC and LHC energies, taking into account the high parton density regime of Quantum Chromodynamics (QCD), where the physics of parton saturation is expected to be dominant. We perform a quantitative analysis of the rapidity distributions in these collisions with the Color Glass Condensate (CGC) approach. The ratio between distributions with or without saturated gluons shows that this mechanism produces a suppression of the J/ψ yield in the forward region only at very high energies.

Quark matter produced in relativistic nuclear collisions is thermally equilibrated. A phenomenological model is used to calculate the yield of strange quark pairs at AGS, SPS and RHIC, which is comparable to the results from the experiments. In addition, analysis with this model indicates that there is a signal of phase transition where the cms energy is approximately 7.5 GeV.

Strange particle production has always been an important probe to study various aspects of the high density, strong interacting matter created in ultra-relativistic heavy-ion collisions. Yields and spectra of strange hadrons have been measured by the STAR experiment for center of mass energies of 62.4 GeV, 130 GeV and 200 GeV per nucleon pair for Au+Au, p+p and d+Au collisions. We have now measured Cu+Cu collisions at 62.4 GeV and 200 GeV, complementing the study of the system size dependence initiated with the centrality dependence study of Au+Au data. We will present preliminary results on Ξ, Ω and their anti-particles produced in Cu+Cu collisions. Yields and ratios are compared to results from Au+Au collisions normalized by the equivalent number of participants. The nuclear modification factor of the measured particles from Cu+Cu data also shows the same suppression effects in the high transverse momentum region and a baryon/meson difference in the intermediate momentum region.

Open charm mesons produced in high energy A-A interactions are expected to be powerful probes to investigate the medium produced in the collision. In this context it is important to measure the production of as many charmed hadrons as possible, such as D⁰, D⁺, and Λ_c, because the measurement of their relative yield can provide information on the hadronization mechanism and is necessary to reduce the systematic error on the absolute cross section. The ALICE experiment at the LHC is designed to perform such measurements at midrapidity down to p_T below 1 GeV/c, mainly by means of the silicon vertex and tracker detector, the time projection chamber and the time of flight detector. One of the main channels for the detection of charm production in ALICE is the exclusive reconstruction of the D⁺ meson through its three charged body decay K⁻π⁺π⁺ in Pb-Pb and pp collisions. The selection strategies for this analysis and the results of a feasibility study on Monte Carlo events will be presented together with the perspectives for the study of D⁺ quenching and azimuthal anisotropy measurements.

Short-lived resonances are useful tools to probe the property of the matter created in heavy ion collisions. Measurements of their production yields and elliptic flow allow us to understand particle production mechanisms as well as the system evolution after hadronization. We report the measurements of transverse momentum (p_T) spectrum and anisotropic parameter v₂ of K* resonance from a high statistics data set of Au+Au collisions at taken by the STAR experiment in year 2004. The K* are measured up to intermediate p_T region p_T < 5 GeV/c at mid-rapidity through its hadronic decay channel. Its nuclear modification factor as well as elliptic flow are compared with corresponding results for and Λ up to intermediate p_T to check the number of constituent quark scaling for resonances. Combined with the K*/K and φ/K* yield ratios, the production mechanism of K* is discussed. The first results on K* m_T spectra from Au+Au 62.4 GeV are presented to understand the energy dependence of K* production.

We present preliminary results of ϒ production in p+p collisions at at central rapidity. This measurement was performed at the STAR experiment through the ϒ → e⁺ e⁻ decay channel. In this manuscript we describe the experimental details, from the development of a specially designed trigger setup to the analysis methods used to discriminate electrons from hadrons. The production cross-section obtained pb is compatible with our expectations based on pQCD calculations.

The experimental data obtained by the Relativistic Heavy Ion Collider (RHIC) have shown surprisingly large elliptic flow and small correlation (Hanbury-Brown-Twiss, HBT) radii. Quark-Gluon String Model (QGSM) is found to reproduce well many of the flow features in heavy-ion collisions, whereas the models based on the longitudinal excitation of strings essentially underpredict the elliptic flow seen at RHIC. Our aim is to study the HBT correlations within the same QGSM approach. The transverse momentum dependence of correlation radii R_long, R_out and R_side obtained in the QGSM is compared with the UrQMD transport model calculations and the experimental STAR data at for the central Au + Au collisions. It appears that the correlation radii obtained in the QGSM from the analysis of all pions are essentially smaller than the experimental ones, while for pions coming from the decay of resonances the agreement with the experimental data is very good.

We demonstrate by using Wiedemann's gluon radiative spectrum that heavy quark radiative energy loss spectrum can be factorized as the light quark radiative energy loss spectrum times a dead cone factor in the absence of medium effect. The availability of factorial approach with a dead cone approximation in medium is studied by Djordjevic-Gyulassy (D-G) and GLV (M.Gyulassy, P.Levai and I.Vitev) formulas. The numerical results show that the factorial method with a dead cone approximation is more suitable for charm quarks than bottom quarks at both RHIC and LHC energies.

The energy loss of heavy quarks traversing color dense matter is calculated with an analytical formula derived within the light-cone path integral (LCPI) approach. We find that the energy loss mechanism is dominated by gluon radiation and induces a suppression pattern of charm quark different from the suppression of light quarks. We find also that this radiative energy-loss is proportional to L² for energetic quarks, but changes to a L dependance with decreasing quark energy, where L is the length of the traversed medium.

The CMS Zero Degree Calorimeters, ZDCs, will measure photons and neutrons emitted with |η| ≥ 8.6 from Pb+Pb, p+Pb and p+p collisions at , 8.8 and 14 TeV respectively. The calorimeter consists of an electromagnetic part segmented in the horizontal direction and an hadronic part segmented into four units in depth. In addition CMS will have access to data from a segmented shower maximum detector being built for luminosity measurements. We will present detailed results from tests beam measurements taken at the CERN SPS. These data will be used to extrapolate the utility of the ZDCs to measure photons, and possibly π₀s in p+p and ultra-peripheral heavy-ion collisions. Data from the hadronic section can be used to estimate the number of participants in heavy ion-collisions. In addition we will discuss plans to use the detector to measure the reaction plane, thereby extending the sensitivity of the central detectors in CMS.

We study the pion electromagnetic form factor and the dilepton production rate in hot matter based on the vector manifestation (VM) of chiral symmetry in which the massless vector meson becomes the chiral partner of the pion, giving a theoretical framework of the dropping ρ à la Brown–Rho scaling. The VM predicts a strong violation of the vector dominance (VD) near the phase transition point associated with the dropping ρ. We present the effect of the VD violation to the dilepton production rate and make a comparison to the one predicted by assuming the VD together with the dropping ρ.

We show the preliminary charged-particle pair correlation analyses presented in a poster session at the 2006 International Quark Matter Conference in Shanghai China. The correlation analysis space of Δφ (azimuth) and Δη (pseudo-rapidity) are considered as a function of centrality for minimum bias Au + Au collisions in the mid-transverse momentum range in the STAR detector. The analyses involve unlike-sign charge pairs and like-sign charge pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We use a multiplicity scale to compare the different centralities. We find the signals increase with increasing centrality. A model featuring dense gluonic hot spots as first proposed by van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur. A blast wave model including multiple hot spots motivates the selection of transverse momenta in the range 0.8 GeV/c < p_t < 4.0 GeV/c.

The PHENIX experiment at RHIC is uniquely suitable for systematic studies of light vector mesons, whose mass states are considered as a sensitive probe of partial chiral symmetry restoration and as a signature of deconfined partonic state of matter. Their challengingly small signal to background ratios in multi body decay channels in heavy ion collisions have been extensively attacked. Significant improvements have been recently achieved of signal extraction techniques. The final results on yields, transverse momentum spectra, and possibly mass states of light vector mesons including φ and ω are well in the near future prospects.

Azimuthal anisotropy of direct photons is measured in Au + Au collisions by the PHENIX experiment at RHIC. Direct photons are one of the most effective probes to study properties of hot dense medium at initial state (also QGP state) of heavy ion collisions because photons do not interact strongly with medium once produced. They keep their conditions when they are created. Within statistical and systematic errors, the elliptic flow parameter (v₂) of direct photons is consistent with zero. Direct photons v₂ is measured by the hadron decay photon background v₂ from inclusive photon v₂ in intermediate to high transverse momentum (p_T) region (0 to 10 GeV/c) for 3 centrality selections (20% steps) and minimum bias.

PHENIX has measured high transverse momentum (p_T) identified hadrons in different collision species and energies in the last five RHIC runs. The systematic study of the high P_T hadron production provides an idea on interaction of hard scattered partons and the matter created in relativistic heavy ion collision. The η/π⁰ ratio is measured in Au + Au collisions, which gives a hint on the system thermalization and particle production. A future measurement of hadron and photon measurement is discussed.

The yields of low mass vector mesons via e⁺e⁻ decay channels in Au + Au collisions at have been measured by the RHIC-PHENIX experiment. The measurement provides important information to study chiral symmetry restoration in high temperature medium created in high energy heavy-ion collisions. One of the major difficulties in the measurement is huge backgrounds due to high multiplicity environments. Analysis methods have been improved to reduce the background. The invariant yield of ω mesons is found to scale with the number of participant nucleons. The invariant p_T spectrum of ω mesons in minimum bias collisions is in a good agreement with other decay channels and in other collision systems.

Direct photon production is an important observable in heavy ion collisions, as photons are penetrating and therefore largely insensitive to final state effects. Measurements of the fragmentation component of direct photon yields in p + p and Au + Au collisions will provide important tests of pQCD predictions and of predictions for modifications of this component in heavy ion collisions. By selecting photons associated with jets on the same side using hadron-photon correlations, fragmentation photons can be measured directly.

In the PHOBOS experiment, charged particles are measured in almost the full solid angle. This enables the study of fluctuations and correlations in the particle production over a very wide kinematic range. In this paper, we show results of a direct search for fluctuations identified by an unusual shape of the pseudorapidity distribution. In addition, we use analysis of correlations of the multiplicity in similar pseudorapidity bins, placed symmetrically in the forward and backward hemispheres, to test the hypothesis of production of particles in clusters.

We present the LHC predictions for the WHDG model of radiative, elastic, and path length fluctuating energy loss. We find the p_⊥ dependence of R_AA is qualitatively very different from AWS-based energy loss extrapolations to the LHC; the large p_⊥ reach of the year one data at the LHC should suffice to distinguish between the two. We also discuss the importance of requiring a first elastic scatter before any medium-induced elastic or radiative loss occurs, a necessary physical effect not considered in any previous models.

The predictions of the two-particle correlation by using the relativistic quantum molecular dynamics model are presented for the heavy-ion reactions at HIRFL-CSR energy. The two-proton correlation function with the final state interaction is calculated with the Lednicky code for the U+U collisions at beam energy 520 A MeV. Applying the imaging technique, the relationship between the freeze-out spatial distributions and the results of correlation femtoscopy is investigated. We find that one can reliably reconstruct the source functions from the two-particle correlation functions with ignoring the degree of space-momentum correlations at this energy. The results are useful to the designing the hadron detector at CSR.

The NA49 experiment at CERN SPS has acquired a huge data set of Pb+Pb events over a broad range of energy and centrality during the last several years. This high statistics data set, coupled with a state-of-the-art analysis technique, allows for the first model-independent extraction and energy scan of 3D emission sources for pion pairs at SPS energies. These 3D pion emission sources provide new insights into the nature of a long-range source previously reported by PHENIX at RHIC. The new results indicate that the pion source displays significant non-Gaussian tails in the longitudinal direction at 40 and 158 AGeV and in the outward direction at 158 AGeV.

Long range forward-backward multiplicity correlations have been measured with the STAR detector for Au+Au collisions at . Strong long range correlations are observed in central Au+Au collisions. Based on the Dual Parton model and Color Glass Condensate considerations the data suggests that these long range correlations are due to multiple parton interactions. This suggests that dense partonic matter is created in central Au+Au collisions at .

We report recent HBT measurements of charged pions in Au+Au and Cu+Cu collisions at by PHENIX at RHIC. The 3-D correlation functions are measured for several centrality and pair momentum regions and 3-D HBT radii are obtained by a traditional Gaussian fit function. By comparing the pion 3-D HBT radii with those measured in Au+Au collisions at , we investigate systematic differences in the 3-D HBT radii as functions of centrality and pair momentum for different collision species and energies.

Qualitative comparison of source sizes from π - Ξ correlations analyses in d+Au and Au+Au collisions at and is presented. For the most central Au+Au collisions at we report first quantitative results concerning size of the π - Ξ source and relative shift of the average emission points between π and Ξ showing that the homogeneity region of Ξ source is smaller then that of pion and significantly shifted in the transverse direction.

Finite volume corrections to higher moments are important observable quantities. They make possible to differentiate between different statistical ensembles even in the thermodynamic limit. It is shown that this property is a universal one. The classical grand canonical distribution is compared to the canonical distribution in the rigorous procedure of approaching the thermodynamic limit.

The current status of the analysis of direct photon Bose-Einstein correlations in Au+Au collisions at done by the PHENIX collaboration is summarized. All possible sources of distortion of the two-photon correlation function are discussed and methods to control them in the PHENIX experiment are presented.

In this paper the study of existance of non-statistical fluctuations using the method of scaled factorial, F_q, moments (SFMs) has been utilized to probe the distribution of relativistic shower particles produced in ²⁸Si-emulsion collisions at 14.6 A GeV. The analysis indicates that the anomalous fractal dimension, d_q, does not favour the origin of any exotic phenomenon. Finally, our data do not show a clear evidence for the existence of non-thermal phase transitions.

We investigate the properties of scalar and pseudo-scalar mesons at finite temperature and quark chemical potential in the framework of the Nambu–Jona-Lasinio (NJL) model coupled to the Polyakov loop (PNJL model) with the aim of taking into account features of both chiral symmetry breaking and deconfinement. In the phase of broken chiral symmetry a narrower width for the σ meson is obtained with respect to the NJL case; on the other hand, the pion still behaves as a Goldstone boson.

We study the Anderson Localization effect on the shear viscosity in a system with random medium by Kubo formula. We show that this effect can reduce the shear viscosity nonperturbatively. Then we discuss its possible implementation in heavy-ion collisions, where the created heavy bound states or other collective modes may play the role of the random scatterer underlying Anderson Localization effect.

We calculate the spectral function of the massive quark at finite temperature (T) using a Yukawa model and show that the peak in the negative energy region among the three-peaks found in a previous work for the massless quark is largely suppressed. To explore the underlying mechanism of this behavior, we also investigate the pole structure of the retarded Green function of the quark. We will show the result only for the massless quark. We find the residues of the poles corresponding the three-peaks are all comparable at T ∼ m_b. We also show that the multi-peak structure of the quark spectra is well described in the pole approximation which indicates that the quasi-particle picture is valid in this T region.

Some thermodynamical properties of the interacting meson system and QGP at finite temperature are discussed. For a pure meson gas the Hagedorn limiting temperature is reproduced when the experimentally observed resonances are included. For QGP our results for different numbers of flavors N_f compare very well to the theoretical ones. A transport model based on the mean free path approach is used to simulate the evolution of the system. During the evolution we use the MIT bag model to perform the transition between meson gas and QGP.

We investigate the chiral phase transition of a QCD-like theory, based the shape change of the effective potential near the critical point. The potential is constructed with the auxiliary field method, and a source term coupled to the field is introduced in order to compute the potential shape numerically. We also generalize the potential so as to have two independent order parameters, the quark scalar density and the number density. We find a tri-critical point locating at (T, μ) = (97, 203) MeV, and visualize it as the merging point of three potential minima.

We investigate a spectrum of a fermion, which we call a quark, above the critical temperature of the chiral phase transition in a gauge theory using the Schwinger–Dyson (SD) equation. The SD equation enables us to study the spectrum over a wide range of the gauge coupling. It is shown that the quark spectrum has two sharp peaks which correspond to the normal quasi-quark and the plasmino and is consistent with that obtained in the hard thermal loop approximation in the weak coupling region, while it has also two peaks but with smaller thermal masses and broader widths in the strong coupling region. Temperature-dependence of the quark spectrum is also discussed.

We review briefly the effects of the running coupling strength, the current quark mass, the density and the finite size of the matter on the QCD phase structure and its transition in the framework of Dyson–Schwinger equation approach of QCD. It provides a visual view to understanding the QCD phase transition with respect to the medium effects and the intrinsic characteristics.

We investigate the mixing among σ and π mesons in pion superfluid in the frame of two flavor NJL model. With the calculated σ and π couplings to quarks, we consider the decay process σ → ππ at finite isospin chemical potential.

Energy dependence of nuclear shadowing and nuclear absorption is discussed in the framework of the Glauber–Gribov model and the AGK cutting rules. We calculate gluon shadowing using recent data on diffractive structure functions from HERA. Phenomenological implications for light particle production at SPS and RHIC are described and compared to charged particle production at mid- and forward rapidities. Comparison of the suppression at these energies leaves nevertheless little room for additional suppression phenomena.

We investigate the phase diagram in the plane of temperature and chemical potential mismatch for an asymmetric fermion superfluid with double- and single-species pairings. There is no mixing of these two types of pairings at fixed chemical potential, but the introduction of the single species pairing cures the magnetic instability at low temperature.

In two flavor neutral quark matter the uniform color superconducting state suffers the chromomagnetic instability at zero temperature. While this instability is extended to low temperature, it is fully cured above a turning temperature. There is a continuous phase transition from some non-uniform phase to the uniform 2SC/g2SC phase at the turning temperature. The introduction of the LOFF state removes the strange temperature behavior of the diquark condensate and significantly changes the phase diagram of neutral dense quark matter.

In the Nambu–Jona-Lasinio model with Polyakov loops, we explore the relation between the deconfinement and chiral phase transitions within the mean-field approximation. We focus on the phase structure of the model and study the susceptibilities associated with corresponding order parameters.

In a first order theory of dissipative hydrodynamics, we have simulated hydrodynamic evolution of QGP fluid with dissipation due to shear viscosity only. Simulation confirms that compared to an ideal fluid, energy density or temperature of a viscous fluid evolve slowly. Transverse expansion is also more in viscous fluid. We also study the effect of viscosity on particle production. Particle production is enhanced, more at large p_T. The elliptic flow on the otherhand decreases and shows a tendency to saturate at large p_T.

We investigate the time evolution of the quantum meson modes in the late time of chiral phase transition. In particular, it is shown that there exists a possible solution to the equation of motion for the quantum meson modes, which reveals a parametric resonance and/or resonance through forced oscillation induced by the small oscillation of the chiral condensate. After that, we demonstrate the unstable regions for the quantum meson modes in both the cases of a uniform and spatially expanding system.

We propose a new hadronization mechanism, jet-fluid string (JFS) formation and decay, to understand observables in intermediate to high-p_T regions comprehensively. In the JFS model, hard partons produced in jet lose their energy in traversing the QGP fluid, which is described by fully three-dimensional hydrodynamic simulations. When a jet parton escapes from the QGP fluid, it picks up a partner parton from a fluid and forms a color singlet string, then it decays to hadrons. We find that high-p_Tv₂ values in JFS are about two times larger than in the independent fragmentation model.

We relate the hyperon polarizations in proton-proton and proton-nucleus collisions to the leading particle effect and use the constituent quark-diquark cascade model with SU(6) wave function. We assume that the quantization axis is characterized by the production normal of the leading baryon of the most massive cascade chain and the incident valence diquark tends to pick up a spin down sea quark or conversely a sea diquark preferentially combines with the spin up incident valence quark to form a leading baryon as compared with the spin down valence quark.

A new channel of direct photon production from a quark gluon plasma (QGP) is explored in the framework of high-temperature QCD. This process appears at next-to-leading order, in the presence of a charge asymmetry in the excited matter. The photon production rate from this new mechanism is suppressed compared to the QCD annihilation and Compton scattering at low baryon density but assumes importance in baryon-rich matter.

We discuss some issues about the relativistic BCS-BEC crossover in a boson-fermion model. These include particle number conservation, chemical equilibrium, the derivation of the thermodynamic potential, the regularization of the gap equation and the BCS ratio.

We present a phase diagram for a fermion pairing system with density imbalance, including homogenous and inhomogeneous phases (LOFF and phase separation). The phase structure of neutron-proton condensate in isospin asymmetric nuclear matter is investigated as a realistic example.

We propose to develop a high-energy heavy-ion experimental database and make it accessible to the scientific community through an on-line interface. The database will be searchable and cross-indexed with relevant publications, including published detector descriptions. It should eventually contain all published data from older heavy-ion programs such as the Bevalac, AGS, SPS and FNAL fixed-target programs, as well as published data from current programs at RHIC and new facilities at GSI (FAIR), KEK/Tsukuba and the LHC collider. This data includes all proton-proton, proton-nucleus to nucleus-nucleus collisions as well as other relevant systems and all measured observables. Such a database would have tremendous scientific payoff as it makes systematic studies easier and allows simpler benchmarking of theoretical models to a broad range of experiments. To enhance the utility of the database, we propose periodic data evaluations and topical reviews. These reviews would provide an alternative and impartial mechanism to resolve discrepancies between published data from rival experiments and between theory and experiment. Since this database will be a community resource, it requires the high-energy nuclear physics community's financial and manpower support.

Using an extension of the Iancu-Itakura-Munier model to nuclear targets we look for saturation effects in electron-ion collisions. In previous publications we have made definite predictions. Here we try to compare our results with already existing experimental data on structure functions and on total and diffractive cross sections. Strictly speaking such a comparison is not well justified because the present data are not yet in the saturation domain. Nevertheless our results agree qualitatively with data and, in some cases, even quantitatively.

We propose a novel method for studying the production of anticentauro events in high energy heavy ion collisions utilizing Chebyshev expansion coefficients. These coefficients have proved to be very efficient in investigating the pattern of fluctuations in neutral pion fraction. For the anticentauro like events, the magnitude of first few coefficients is strongly enhanced (≈ 3 times) as compared to those of normal HIJING events. Various characteristics of Chebyshev coefficients are studied in detail and the probability of formation of exotic events is calculated from the simulated events.

We compute pion-nucleon scattering at tree-level within a gauged linear sigma model which contains the nucleon and its chiral partner. Such an investigation in principle allows to make definite predictions as to whether the main contribution to the nucleon mass comes from the chiral condensate or from the mixing with its chiral partner. We find that there seems to be no set of model parameters that allows for a simultaneous description of all experimentally measured scattering lengths and range parameters. This indicates the need to improve the dynamical ingredients of the model.

We study effects of a thermal-quark mass and Landau damping of quarks on the chiral phase transition and its soft modes at finite temperature. For this purpose we employ a simple model with the quark propagator obtained in the hard thermal loop approximation. We show that the chiral phase transition is second order even if quark have a finite thermal mass, and the thermal mass suppresses the chiral condensate. We argue that mesonic spectra have a large width due to scattering between gluons and quarks, and the van Hove singularity at threshold.¹.

We have built an effective Walecka-type hadronic Lagrangian in which the hadron masses and the density dependence of the coupling constants are deduced from the quark dynamics using a Nambu–Jona-Lasinio model. In order to stabilize nuclear matter an eight-quark term has been included. The parameters of this Nambu–Jona-Lasinio model have been determined using the meson properties in the vacuum but also in the medium through the omega meson mass in nuclei measured by the TAPS collaboration. Realistic properties of nuclear matter have been obtained.

This paper gives some results about trigger decision criterion of the ALICE PHOton Spectrometer (PHOS) by Monte Carlo simulations, including four parts: (1) an overview of trigger decision criterion of PHOS; (2) the energy reconstruction performance of PHOS; (3) the selection of trigger threshold and the event trigger efficiency distribution; (4) the photon event trigger rate of PHOS in p–p interactions and Pb–Pb collisions.

The large TPC (95 m³) of the ALICE detector at the CERN LHC was commissioned in summer 2006. The first tracks were observed both from the cosmic ray muons and from the laser rays injected into the TPC. In this article the basic principles of operating the 266 nm lasers are presented, showing the installation and adjustment of the optical system and describing the control system. To generate the laser tracks, a wide laser beam is split into several hundred narrow beams by fixed micro-mirrors at stable and known positions throughout the TPC. In the drift volume, these narrow beams generate straight tracks at many angles. Here we describe the generation of the first tracks and compare them with simulations.

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt will be a dedicated heavy-ion experiment exploring the QCD phase diagram in the region of moderate temperatures but very high baryon densities. The currently foreseen CBM detector setup, physics observables of interest, and first feasibility studies of their measurement will be presented.

We present the production procedure and the quality assurance process of gas gaps for the forward resistive plate chambers of the CMS detector at LHC/CERN. We also present the results from an aging study performed by using a gamma ray source. No significant aging effect was observed because of intense gamma irradiation, equivalent to approximately 12 years of the CMS operation.

The ALICE Forward Multiplicity Detector (FMD) is a silicon strip detector with 51,200 strips arranged in 5 rings, covering the range −3.4 < η < 5.1. It is placed around the beam pipe at small angles to extend the charged particle acceptance of ALICE into the forward regions, not covered by the central barrel detectors.

ALICE, the dedicated heavy ion experiment at the LHC, will also have an important impact on the proton-proton physics program. The physics analyses foreseen with the ALICE muon spectrometer are reviewed. A particular emphasis is placed on heavy flavor measurement.

The Inner Tracking System (ITS) of ALICE consists of six silicon layers. The two innermost (SPD) are made of pixeldetectors. The middle layers (SDD) contain silicon driftdetectors, whereas the two outer layers are made of double-sided silicon stripdetectors. Its layout and performance is described.

Cosmic-rays sometimes produce showers of unusual composition that contain particles with energy-loss profiles different from all known particles. The Large Hadron Collider (LHC) will produce, for the first time, nuclear collisions at the extremely high energy characteristic of the cosmic-ray events. The CASTOR detector, a part of the huge CMS experiment, is designed for detailed studies of the products corresponding to the cores of cosmic-ray showers. It will cover angles of 0.1° to 0.7° from the beam. It will be divided azimuthally into 16 segments and longitudinally into 18 segments. It is assumed that cosmic ray showers are caused by nuclei, protons through iron, hitting the atmosphere. If CASTOR does not find events that can be identified with the anomalous cosmic-ray events, this assumption may need to be reconsidered. Pb-Pb collisions with the LHC will have an energy 28 times that of Au-Au collisions studied at RHIC. With this huge increase in energy a wealth of new phenomena is almost assured. Because of the much larger mass number, Pb-Pb events can be expected to show exotic phenomena that is beyond the reach of cosmic rays.

Using a test TPC, consisting of the ALICE TPC field cage prototype in combination with the final ALICE TPC readout and electronics, the energy loss distribution and resolution were measured for identified protons. The measurements were compared to theoretical calculations and good quantitative agreement was found when detector effects were taken into account. The implications for particle identification are discussed.

The ability of the ALICE detector to reconstruct the K*(892)⁰ resonance in p–p and Pb–Pb collisions at LHC energies has been investigated, by means of a detailed study of simulated events. PYTHIA events for p–p collisions and HIJING events for Pb–Pb collisions have been generated and fully reconstructed. The K*(892)⁰ was identified by its hadronic decay into Kπ through invariant mass analysis. The combinatorial background has been estimated using an event-mixing technique for p–p events and a like-sign technique for the Pb–Pb ones. The role of the particle identification of the decay product is also discussed.

This poster presents an alternate method for the estimation of detector acceptance and efficiency based on PHENIX Run 4 AuAu central spectrometer data sample and its application to J/ψ invariant yield calculation. After some descriptions of the data set used and comparison of results from this method with the published results from PHENIX, we show a very brief comparison of the latter to theoretical calculation.

Time-Of-Flight (TOF) based on Multi-gap Resistive Plate Chamber (MRPC) detectors have been successfully operating at the STAR experiment since 2003.^2,3 The MRPC time resolution is however found to be significantly worse² (80-90 ps) than that previously obtained in beam test (60 ps).⁴ In order to fully understand MRPC working principles and operating requirements, an extensive calibration study is performed using data collected by STAR in 200 GeV Au+Au collisions in 2004. The relation between MRPC timing, signal amplitude, incident angle and momentum are discussed. Contributions from tracking properties of STAR-TPC are also studied by simulation. The intrinsic time resolution of the MRPCs used in STAR-TOF, after taking all factors into consideration, is found to be in good agreement with beam test results.

A Large Ion Collider Experiment – ALICE will become operational with the startup of the Large Hadron Collider – LHC at the end of 2007. One focus of the physics program is the measurement of quarkonia in proton-proton and lead-lead collisions. Quarkonia states will be measured in two kinematic regions and channels: di-muonic decays will be measured in the forward region by the muon arm, the central part of the detector will measure di-electronic decays. The presented studies show the expected performance of the di-electron measurement in proton-proton and central lead-lead collisions.

We present background studies for single muon measurements in Au+Au collisions at . To estimate the background coming from the high multiplicity, we applied the half octant swapping method. The swapped data was compared with the real data, and we know that the background ratio doesn't depend on the vertex distribution as already expected.

The new Time-of-Flight (TOF) subsystem for STAR at RHIC will have 3840 6-pad Multigap Resistive Plate Chambers (MRPC) distributed over 120 trays. Each tray contains 192 channels and three types of electronics cards: “TINO”, “TDIG” and “TCPU”. Every 30 trays send data to a “THUB” card that interfaces to STAR trigger and transmits data over fiber to a STAR DAQ fiber receiver. TINO contains analog front end electronics based on the CERN/LAA NINO custom IC. TDIG digitizes the data using the CERN HPTDC ASIC. TCPU formats and buffers the digital information.

A cosmic ray test system comprised of three plastic scintillators, 4 MRPC modules, and TOF prototype electronics is used to determine the timing resolution to be achieved for the entire TOF system. Overall timing resolution of 80 – 110 ps has been achieved.

The silicon pixel detector of the ALICE experiment at LHC comprises the two innermost layers in the inner tracking system of the apparatus. It contains 1200 readout chips, each of them corresponding to a 8192 pixel matrix. The single chip outputs a digital Fast-OR signal which is active whenever at least one of the pixels in the matrix records a hit.

The 1200 Fast-OR signals can be used to implement a triggering capability: a few details on the pixel trigger system and some of the possible applications for the event selection in p-p collisions are presented.

The Silicon Vertex Tracker (VTX) for the Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) at the Brookhaven National Laboratory (BNL) will be installed into the innermost of PHENIX detector in 2009. The VTX will enhance physics capability of PHENIX. The first read-out and cosmic telescope test for pixel with almost actual read-out system had achieved successfully in last year, 2006.

Transverse momentum spectra of π^± at midrapidity are measured at high p_T in p+p and p+Pb collisions at 158 GeV/nucleon beam energy by the NA49 experiment. This study is complementary to our previous results on the same spectra from Pb+Pb collisions. The nuclear modification factors R_A+A/p+p, R_p+A/p+p and R_A+A/p+A as a function of p_T are extracted and compared to RHIC measurements, thus providing insight into the energy dependence of nuclear modification. The modification factor R_A+A/p+A proved to be consistent with our previous results on the central to peripheral modification factor R_CP.

The limitation of our current p_T range is discussed and planned future upgrades are outlined. Some aspects of the FAIR-CBM experiment are also presented as a natural future continuation of the measurements at very high p_T.

Building of ATLAS is progressing well towards recording first pp collisions at 0.9 TeV in 2007, pp at 14 TeV in 2008 and hopefully PbPb soon later. The complexity of the detector is illustrated and several observables interesting for heavy-ion physics are discussed.

Based on flow measurements at the SPS and RHIC, the expected values of elliptic flow and charged multiplicity have been extrapolated as a function of the impact parameter to LHC energy. Those predictions have been used as an input for ALICE simulation, to develop and test a flow analysis package for the ALICE environment. The Event Plane analysis has provided an estimate of the event plane resolution at the LHC and it has also been applied to Hijing events generated with no genuine elliptic flow. In this kind of environment it has been possible to study the effects on v₂ from pure non-flow effects, and thus get an estimate of the systematics due to non-flow.

PHENIX Vertex Tracker will be installed in 2009 in order to enhance the physics capability in both heavy ion and spin program. It is designed to separate bottom and charm quark production by measuring distance closest approach even in the heavy ion collision and identifying jet in the polarized proton-proton collisions. The detector consists of two inner pixel layers and two outer stripixel layers. The stripixel sensor is single sided two dimensional silicon strip sensor. It will be suffered by the radiation damage up to 4fb⁻¹ of integrated luminosity over 10 years of RHIC running period. In our case the damage will increase leakage current from the sensor and degraded front end electronics performance. This article will describe the radiation damage study for the stripixel sensor.

Multi-gap resistive plate camber (MRPC) has been demonstrated to have good time resolution (less than 100 ps), high detection efficiency (higher than 95%) and will be used to construct a full barrel time-of-flight (TOF) detector for the STAR experiment at RHIC. The cylindrical TOF covers a total area of approximately 64 m² and about 4000 MRPC modules will be produced. Tsinghua University and University of Science and Technology of China (USTC) are responsible for the STAR MRPC production. In this paper we will describe the Tsinghua and USTC MRPC production facilities. Our MRPC manufacture procedures, detector assembly and testing results are also presented.

We will summarize how future measurements of electromagnetic probes at the upgraded Relativistic Heavy Ion Collider (RHIC-II), in connection with theoretical analysis, can advance our understanding of strongly interacting matter at high energy densities and temperatures. Electromagnetic probes have already played a very important role at SPS and RHIC to date. We will try to identify key physics objectives and observables that remain to be addressed. These include measuring the initial temperature and examining the transition properties via continuum radiation, studying the energy loss mechanism in the medium, the system size evolution via photon-photon correlations as well as medium modifications of vector mesons via low-mass dileptons. We will argue that detector upgrades, increased experimental precision, order of magnitude higher statistics than currently achievable, as well as a detailed scan of colliding species and energies are necessary to allow for sufficient discrimination power in theoretical interpretations.