We report BRAHMS results from RHIC d+Au and p+p collisions at √{sNN} = 200 GeV. A remarkable change in the nuclear modification factor RdAu is seen as the pseudorapidity of the detected charged hadrons changes from zero at mid-rapidity to 3.2 at the most forward angle studied during the 2003 run. For pseudorapidity η > 1 the suppression of the Rcp factor is more pronounced in the sample of central events in contrast to the behavior at mid-rapidity where the central events show higher enhancement compared to a semi-central sample. These results are consistent with a saturated Au wave function strongly affected by quantum evolution at higher values of rapidity.
The J/ψπ → ]]>]]>]]>]]>]]>\bar{\rm D}{\rm D}^*$, D$\bar{\rm D}^*$, $\bar{\rm D}$D and $\bar{\rm D}^*$D$^*$ cross sections as a function of √{s} are evaluated in a QCD sum rule calculation. We find that our results are compatible with the J/ψπ → charmed mesons cross sections obtained with models based on meson exchange if a cut-off of order of 1 GeV is used.
We present a detailed study of chemical freeze-out in nucleus–nucleus collisions at beam energies of 11.6, 30, 40, 80 and 158A GeV. By analyzing hadronic multiplicities within the statistical hadronization approach, we have studied the chemical equilibration of the system as a function of center of mass energy and of the parameters of the source. Additionally, we have tested and compared different versions of the statistical model, with special emphasis on possible explanations of the observed strangeness hadronic phase space under-saturation.
A critical discussion of the present status of the CERN experiments on charm dynamics and hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A GeV: here the hydrodynamic model has predicted the collapse of the v1-flow and of the v2-flow at ∼10A GeV; at 40 A GeV it has been recently observed by the NA49 Collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as evidence for a first order phase transition at high baryon density ρB. A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Here, hadronic rescattering models can explain <30% of the observed elliptic flow, v2, for pT>2GeV/c. This is interpreted as evidence for the production of superdense matter at RHIC with initial pressure far above hadronic pressure, p>1GeV/fm3. We suggest that the fluctuations in the flow, v1 and v2, should be measured in future since ideal hydrodynamics predicts that they are larger than 50% due to initial state fluctuations. Furthermore, the QGP coefficient of viscosity may be determined experimentally from the fluctuations observed. The connection of v2 to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the away-side jet suppression can only partially (<50%) be due to hadronic rescattering. We, finally, propose upgrades and second generation experiments at RHIC which inspect the first order phase transition in the fragmentation region, i.e., at μB≈400MeV (y≈4–5), where the collapse of the proton flow should be seen in analogy to the 40 A GeV data. The study of Jet-Wake-riding potentials and Bow shocks—caused by jets in the QGP formed at RHIC—can give further information on the equation of state (EoS) and transport coefficients of the quark–gluon plasma (QGP).
We present the first measurement of directed flow (v1) at the Relativistic Heavy Ion Collider (RHIC). v1 is found to be consistent with zero at pseudorapidities η from -1.2 to 1.2, then rises to the level of a couple of percent over the range 2.4 < |η| < 4. The latter observation is similar to that from NA49 if the SPS rapidities are shifted by the difference in beam rapidity between RHIC and SPS. We studied the evolution of elliptic flow from p+p collisions through d+Au collision, and onto Au+Au collisions. Measurements of higher harmonics are presented and discussed.
We present measurements of dynamical net charge fluctuations in Au+Au collisions at √{sNN} = 0, 130 and 200 GeV using the measure ν+-, dyn. The dynamical fluctuations are finite and exhibit a rather modest dependence on beam energy. We also find they violate the trivial 1/N scaling expected for nuclear collisions consisting of independent nucleon–nucleon interactions. We speculate this may be due to a combination of thermalization and radial flow effects.
We present preliminary results of the STAR experiment at RHIC on exotic particle searches in minimum bias Au+Au collisions at √{sNN} = 200 GeV. We observe a narrow peak at 1734 ± 0.5 ± 5 MeV in the Λ K0 s invariant mass with width consistent with the experimental resolution of about 6 MeV within the errors. The statistical significance can be quantified between 3 and 6 σ depending on cuts and methods. If this peak corresponds to a real particle state it would be a candidate for the N0 or the Ξ0 I = ˝ pentaquark states.
We discuss the hadron production in heavy ion collisions by the recombination and fragmentation model. We propose the elliptic flow as the useful tool for exploring final interactions for resonances, hadron structure for exotic particles and phase structure.
Preliminary strangeness enhancement factors measured in pp, d–Au and Au–Au collisions at RHIC will be discussed and compared to model predictions. The impact of elementary collision effects, such as Cronin enhancement and jet production, on collective parameters measured in Au–Au collisions, e.g. radial expansion and <pt> distributions, will be discussed.
We here give an overview of the main results for heavy quark energy loss in a hot QCD matter. The results are used to compute charm quark suppression and elliptic flow at RHIC. Our numerical estimates predict only small suppression of high p⊥ charm quarks.
This paper reviews recent results on directed and elliptic flow from the PHOBOS experiment using data taken during Au+Au runs at RHIC. The systematic dependence of flow on pseudorapidity, energy, transverse momentum and centrality is discussed.
This contribution presents general features of the hadron physics program developed at the Thomas Jefferson Laboratory. This is made using the EM and Weak probes provided by the electron beams of the CEBAF accelerator and address mostly the non-perturbative regime of QCD.
Measurements using the finely segmented EM Calorimeter in PHENIX are presented. The issue of whether these are sufficient to claim discovery of the Quark Gluon Plasma is discussed.
Directed and elliptic event anisotropy parameters measured in the experiments at relativistic heavy-ion collider are presented. The possible origin of the measured elliptic anisotropy parameter $v_2$ and its sensitivity to the early phase of the high-energy heavy-ion collisions are discussed.
The LHC will collide protons at √{s} = 14 TeV and lead ions at √{sNN} = 5.5 TeV. These energies are much higher than with the Fermilab Tevatron or RHIC. Huge experiments are being assembled at four interaction points along the 27 km LHC ring. Although it is a large step into the unknown, there have been extensive calculations predicting data rates for a wide variety of processes to be observed by these experiments. Here we consider primarily the results of lead collisions as will be observed by the CMS experiment.
The properties of jets produced in p+p, d+Au and Au+Au collisions at sqrts_NN=200 GeV are studied using the method of two particle correlations. The trigger particle is assumed to be a leading particle from a high p_T jet while the associated particle is assumed to come from either the same jet or the away jet. From the angular width and yield of the same and away side correlation peaks, the parameters characterizing the jet properties are extracted.
Several correlation analysis techniques are applied to p-p and Au-Au collisions at RHIC. Strong large-momentum-scale correlations are observed which can be related to local charge and momentum conservation during hadronization and to minijet (minimum-bias parton fragment) correlations.
In this contribution the energy dependence of various hadronic observables as measured by the NA49 experiment in the beam energy range between 20 and 158 AGeV is presented. These include mt and rapidity distributions, particle ratio fluctuations, as well as HBT radii. The data are put in the context of results from the AGS and RHIC.
Investigation of the final hadronic state properties of ultra-relativistic pp and Au+Au collisions supplies information on freeze-out conditions at RHIC and possible insights into early stages of these collisions. A variety of particle spectra measured by STAR are studied within the framework of chemical and local kinetic equilibrium models. Here we present the extracted chemical and final kinetic freeze-out temperatures, strangeness saturation factor, final collective flow velocity, and the inferred flow velocity at chemical freeze-out. In light of those measurements we discuss dynamical evolution of the collision system.
