Statistical Model Of Particle Production Research Articles

Σ0 production in proton nucleus collisions near threshold

The production of Σ0 baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to sNN=3.18 GeV) is studied with the detector set-up HADES at GSI, Darmstadt. Σ0s were identified via the decay Σ0→Λγ with subsequent decays Λ→pπ− in coincidence with a e+e− pair from either external (γ→e+e−) or internal (Dalitz decay γ⁎→e+e−) gamma conversions. The differential Σ0 cross section integrated over the detector acceptance, i.e. the rapidity interval 0.5<y<1.1, has been extracted as ΔσΣ0=2.3±(0.2)stat±(−0.6+0.6)sys±(0.2)norm mb, yielding the inclusive production cross section in full phase space σΣ0total=5.8±(0.5)stat±(−1.4+1.4)sys±(0.6)norm±(1.7)extrapol mb by averaging over different extrapolation methods. The Λall/Σ0 ratio within the HADES acceptance is equal to 2.3±(0.2)stat±(−0.6+0.6)sys. The obtained rapidity and momentum distributions are compared to transport model calculations. The Σ0 yield agrees with the statistical model of particle production in nuclear reactions.

Bose--Einstein Correlations and Thermal Cluster Formation in High-energy Collisions

The blast wave model is generalized to include the production of thermal clusters, as suggested by the apparent success of the statistical model of particle production at high energies. The formulae for the HBT correlation functions and the corresponding HBT radii are derived.

Statistical hadronization phenomenology in K/π fluctuations at ultra-relativistic energies

We discuss the information that can be obtained from an analysis of fluctuations in heavy-ion collisions within the context of the statistical model of particle production. We then examine the recently published experimental data on ratio fluctuations, and use it to obtain constraints on the statistical properties (physically relevant ensemble, degree of chemical equilibration, scaling across energies and system sizes) and freeze-out dynamics (amount of reinteraction between chemical and thermal freeze-out) of the system.

Phenomenology of strangeness enhancement in heavy-ion collisions

We give an overview of the phenomenology of strangeness enhancement in heavy-ion collisions, within the paradigm of the statistical model of particle production. We argue that, while strangeness enhancement data are suggestive of a phase transition, the mechanism triggering enhancement is still elusive. We study the feasibility to constrain this mechanism by determining the scaling variable of strangeness enhancement. We further argue that to test the applicability of the statistical model generally, and to confirm our interpretation of the statistical physics responsible for strangeness enhancement, the scaling of strange particle fluctuations (K/π and other particles) w.r.t. yields has to be explored.

Fluctuations of particle ratios as a freeze-out probe

We explain how event-by-event fluctuations of particle ratios can constrain and falsify the statistical model of particle production in heavy-ion collisions, using K/π fluctuations as an example. We define an observable capable of determining which statistical model, if any, governs freeze-out in ultrarelativistic heavy-ion collisions. We calculate this observable for K/π fluctuations, and show that it should be the same for RHIC and LHC energies, as well as independent of centrality, if the grand canonical statistical model is an appropriate description and chemical equilibrium applies. We describe what happens in case of deviations from this scenario, such as light quark chemical non-equilibrium, strange quark over-saturation and local conservation (canonical ensemble) for strange quarks. We also introduce a similar observable capable, together with the published K*/K measurement, of ascertaining if an interacting hadron gas phase governs the system between thermal and chemical freeze-out, and of ascertaining its duration and impact on hadronic chemistry

Overview of results from PHOBOS experiment at RHIC

An overview of results for interactions of Au+Au ions at centre-of-mass energies of √sNN = 56, 130 and 200 GeV obtained by the PHOBOS collaboration at RHIC is given. Measurements of primary charged particle density near mid-rapidity indicate that particle production grows logarithmically with collision energy and faster than linearly with the number of interacting nucleons. Elliptic flow is found to be much stronger at RHIC than at SPS energy. The effect is strongest in peripheral events and decreases for more central collisions and emission angles |η| > 1. The measured anti-particle to particle ratios of production rates for pions, kaons and protons in central Au+Au interactions at √sNN = 130 GeV are compatible with the statistical model of particle production, showing an increasingly baryon-free region in mid-rapidity with the increase of collision energy.

THREE-DIMENSIONAL STATISTICAL MODEL FOR DENSITY FLUCTUATIONS IN HEAVY ION COLLISIONS

A statistical model of particle production is presented using a Gaussian functional in three dimensions. Identifying the field with the particle density fluctuation results in zero cumulant correlations of order three and higher, while the second order correlation function is of a Yukawa form. The model predicts a parameter-free asymptotic slope of unity for the three-dimensional vertical cumulant. A detailed scheme for projecting the theoretical three-dimensional correlation illustrates how theoretical predictions are tested against experimental moments in the different dimensions. Examples given using NA35 rapidity and p⊥ distributions should be testable against future NA35 and other data.

A statistical interpretation of large-angle elastic scattering

The statistical model of particle production makes definite predictions about «compound-elastic» scattering cross-sections. Such predictions are available in a numerical form for π-N and p-p collisions with primary energy (laboratory-system) between zero and about 20 to 30 GeV. The result is that the «compound-elastic» cross-section for π-N should show the following dependence on the total centre-of-momentum energyE (measured in GeV):\(4\pi \frac{{d\sigma _{e1} }}{{d\Omega }}|_{large angles} \equiv \left\langle {\sigma _E } \right\rangle \approx \sigma _{ine1} ^ - \exp \left[ { - 3.17\left( {E - 1.40} \right) \cdot f\left( E \right)} \right]\) wheref(E) is a slowly varying function representing the «inelasticity». Experimental results are compared to this prediction and qualitative agreement is found.

Resonant statistical model of particle production

The statistical model modified to include resonant interaction is discussed. It is shown that arbitrary mass-squared distributions calculated from Lorentz invariant phase space can be expressed as a product of two phase-space factors. Expressions arising in the modified model are reduced to either products of phase-space factors or simple integrals over such products. Application to nucleon-antinucleon annihilation into pions is given. Results are presented for the reaction p+-p→ 2π++2π-+π0 at antiproton momentum 1.61 GeV/c, and the observed three-pion mass distributions are fitted with a half-width for the ω resonance of (10.1±2.9) MeV.

A new technique in the statistical model of particle production

A new method is introduced to account for conservation laws in the. statistical model of particle production. The approach becomes exact in the limit of high multiplicities: it leads to simple analytical expressions which allow immediate estimates of the influence of the various conservation laws under different circumstances. Momentum conservation is shown to have little influence on the energy spectra of the emitted particles; its consequences for the angular correlation of particles are studied. The statistical weight factors, which result from the coupling of the isospin vectors of the emitted particles with isospin conservation imposed, are shown to be well represented by semi-classical expressions; the dependence of the weight factors on total isospin and multiplicity becomes obvious. The general effects of angular momentum conservation in the statistical model are studied; the angular distributions are forward-backward symmetric in the c.m. system, a prediction specific to the model and a suitable test to its validity. In the classical approximation the angular distribution is forward-backward peaked, though not more than a limiting distribution 1/sinθ, whereθ is the angle of the particle with the beam direction. Angular momentum conservation leaves energy spectra nearly unchanged, while multiplicities are strongly affected by it; the effective interaction volumes in nucleon-antinucleon annihilation and nucleon-nucleon collisions are shown to be approximately the same, when this effect is taken into account.