The assumption of simultaneous chemical and thermal freeze-outs of the hadron gas leads to a surprisingly accurate, albeit entirely conventional, explanation of the recently-measured RHIC p ⊥ -spectra. The original thermal spectra are supplied with secondaries from cascade decays of all resonances, and subsequently folded with a suitably parameterized expansion involving longitudinal and transverse flow. The predictions of this thermal approach, with various parametrizations for the expansion, are in a striking quantitative agreement with the data in the whole available range of 0 ≤ p ⊥ ≤ 3.5GeV. 25.75.Dw, 25.75.Ld In this Letter we offer a very simple explanation of the p ⊥ -spectra recently measured at RHIC [1][2][3]. Our approach has the following ingredients: i) simultaneous chemical and thermal freeze-outs, with the hadron distributions given by the thermal model; in other words, hadrons decouple completely when the thermodynamic parameters reach the freezing conditions, and no particle rescattering after freeze-out is present, ii) these thermal distributions are folded with a suitably parameterized hydrodynamic expansion, involving longitudinal and transverse flow, finally, iii) feeding from resonances, including cascades, is incorporated in a complete way.So far, the thermal approach has been applied successfully in studies of particle ratios measured in relativistic heavy-ion collisions at AGS and SPS [4][5][6][7][8][9][10]. Quite recently, it has also been shown that particle ratios measured at RHIC may be equally well described in the framework of such models [11][12][13]. Description of hadronic p ⊥ -spectra in thermal models is more involved, since the spectra are affected by decays of resonances, hydrodynamic flow, and possibly by other phenomena occurring during the alleged phase transition from the quark-gluon plasma to a hadron gas [14]. The model results presented in this Letter are in a surprising agreement with the experiment in the entire range of the data, 0 ≤ p ⊥ ≤ 3.5GeV, as can be seen in Fig. 1. The model has two free parameters: one controlling the size of the system (overall normalization of the spectra), and the other one the transverse flow. We test two different models (parametrizations) for the freeze-out hypersurface and the hydrodynamic expansion. Both combine the Bjorken expansion [15] with transverse flow [16,17], and follow the spirit of Refs. [18][19][20][21][22].The first model (model I) assumes that the freezeout takes place at a fixed value of the invariant time, τ = t 2 − r 2 z − r 2 x − r 2 y = const, which means that, due to time dilation, the particles in the fluid elements moving farther away from the collision center decouple later than the particles in the fluid elements remaining at rest in the center-of-mass system of the colliding nuclei. Furthermore, we assume that the four-velocity of expansion is proportional to the coordinate,The freeze-out hypersurface is parameterized as [20]where α is the rapidity of the fluid element (v z = r z /t = tanh α ), whereas ...

We explore predictions of the wounded quark model for particle production and properties of the initial state formed in ultrarelativistic heavy-ion collisions. The approach is applied uniformly to A+A collisions in a wide collision energy range, as well as for p+A and p+p collisions at the CERN Large Hadron Collider (LHC). We find that generically the predictions from wounded quarks for such features as eccentricities or initial sizes are close (within 15%) to predictions of the wounded nucleon model with an amended binary component. A larger difference is found for the size in p+Pb system, where the wounded quark model yields a smaller (more compact) initial fireball than the standard wounded nucleon model. The inclusion of subnucleonic degrees of freedom allows us to analyze p+p collisions in an analogous way, with predictions that can be used in further collective evolution. The approximate linear dependence of particle production in A+A collisions on the number of wounded quarks, as found in previous studies, makes the approach based on wounded quarks natural. Importantly, at the LHC energies we find approximate uniformity in particle production from wounded quarks, where at a given collision energy per nucleon pair similar production of initial entropy per source is needed to explain the particle production from p+p collisions up to A+A collisions. We also discuss the sensitivity of the wounded quark model predictions to distribution of quarks in nucleons, distribution of nucleons in nuclei, and to the quark-quark inelasticity profile in the impact parameter. In our procedure, the quark-quark inelasticity profile is chosen in such a way that the experiment-based parametrization of the proton-proton inelasticity profile is properly reproduced. The parameters of the overlaid multiplicity distribution is fixed from p+p and p+Pb data.PACS numbers: 25.75Gz, 25.75.Ld

We present a Monte-Carlo generator for a variety of Glauber-like models (the wounded-nucleon model, binary collisions model, mixed model, model with hot spots). These models describe the early stages of relativistic heavy-ion collisions, in particular the spatial distribution of the transverse energy deposition which ultimately leads to production of particles from the interaction region. The original geometric distribution of sources in the transverse plane can be superimposed with a statistical distribution simulating the dispersion in the generated transverse energy in each individual collision. The program generates inter alia the fixed-axes (standard) and variable-axes (participant) two-dimensional profiles of the density of sources in the transverse plane and their azimuthal Fourier components. These profiles can be used in further analysis of physical phenomena, such as the jet quenching, event-by-event hydrodynamics, or analysis of the elliptic flow and its fluctuations. Characteristics of the event (multiplicities, eccentricities, Fourier coefficients, etc.) are stored in a ROOT file and can be analyzed off-line. In particular, event-by-event studies can be carried out in a simple way. A number of ROOT scripts is provided for that purpose. Supplied variants of the code can also be used for the proton-nucleus and deuteron-nucleus collisions.

Scalar-isoscalar states (J P C = 0 ++ ) are investigated within the large-Nc Regge approach. We elaborate on the consequences of including the lightest f0(600) scalar-isoscalar state into such an analysis, where the position of f0(600) fits very well into the pattern of the radial Regge trajectory. Furthermore, we point out that the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice, provide valuable information on the low-mass spectrum of the scalarisoscalar states on the basis of the scalar-meson dominance in the spin-0 channel. Through the fits to these data we find mσ = 450 − 600 MeV. We compare the predictions of various fits and methods. An analysis of the QCD condensates in the two-point correlators provides further constraints on the parameters of the scalar-isoscalar sector. We find that a simple two-state model suggests a meson nature of f0 (600), and a glueball nature of f0 (980), which naturally explains the ratios of various coupling constants. Finally, we note that the fine-tuned condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states yields a reasonable value for the mass of the lighest glueball state.

We analyze the proton-lead collisions at the CERN Large Hadron Collider energy of √ s NN = 5.02 TeV in the three-stage approach, previously used to successfully describe the relativistic A-A collisions. The approach consists of the early phase, modeled with the Glauber model, the event-by-event viscous 3 + 1 dimensional (3 + 1 D) relativistic hydrodynamics, and the statistical hadronization at freeze-out. We show that features typical of collective dynamics, such as the harmonic flow and the ridge structures in the two-particle correlations in relative azimuth and pseudorapidity, may be naturally explained in our framework. In the proton-nucleus system the harmonic flow is generated from an initially event-by-event deformed system and is entirely due to these initial fluctuations. Notably, fluctuations of strength of the initial Glauber sources which yield the observed distribution of hadron multiplicities and, at the same time, lead to correct values of the elliptic flow coefficients both from the two-and four-particle cumulant method, as measured by the ATLAS collaboration. The azimuthally asymmetric flow is not modified significantly when changing the viscosity coefficient, the initial time for the collective expansion, or the initial size of the fireball. The results present an estimate of the collective component in the two-particle correlations measured experimentally. We demonstrate that the harmonic flow coefficients can be experimentally measured with methods based on large rapidity gaps which reduce some of the other sources of correlations.

We investigate the hydrodynamic evolution of the system formed in ultrarelativistic heavy-ion collisions and find that an appropriate choice of the initial condition, specifically a simple two-dimensional Gaussian profile for the transverse energy, in conjunction with a realistic equation of state, leads to a uniform description of soft observables measured at the relativistic heavy-ion collider. In particular, the transverse-momentum spectra, the elliptic-flow, and the Hanbury-Brown-Twiss correlation radii, including the ratio Rout/Rside as well as the dependence of the radii on the azimuthal angle, are all properly described.

SHARE is a collection of programs designed for the statistical analysis of particle production in relativistic heavy-ion collisions. With the physical input of intensive statistical parameters, it generates the ratios of particle abundances. The program includes cascade decays of all confirmed resonances from the Particle Data Tables. The complete treatment of these resonances has been known to be a crucial factor behind the success of the statistical approach. An optional feature implemented is a Breit-Wigner type distribution for strong resonances. An interface for fitting the parameters of the model to the experimental data is provided.

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