Non-identical Particle Research Articles

Non-identical particle femtoscopy in models with single freeze-out

We present femtoscopic results from hydrodynamics-inspired thermal models with single freeze-out. Non-identical particle femtoscopy is studied and compared to results of identical particle correlations. Special emphasis is put on shifts between average space-time emission points of non-identical particles of different masses. They are found to be sensitive to both the spatial shift coming from radial flow, as well as average emission time difference coming from the resonance decays. The Therminator Monte-Carlo program was chosen for this study because it realistically models both of these effects. In order to analyze the results we present and test the methodology of non-identical particle correlations.

Selected results on strong and coulomb-induced correlations from the STAR experiment

Using recent high-statistics STAR data from Au+Au and Cu+Cu collisions at full RHIC energy I discuss strong and Coulomb-induced final state interaction effects on identical ($\pi-\pi$) and non-identical ($\pi-\Xi$) particle correlations. Analysis of $\pi-\Xi$ correlations reveals the strong and Coulomb-induced FSI effects allowing for the first time to estimate space extension of $\pi$ and $\Xi$ sources and average shift between them. Source imaging technique providing clean separation of these effects from effects due to the source function itself is applied to one-dimensional relative momentum correlation function of identical pions. For low momentum pions and/or non-central collisions large departure from a single-Gaussian shape is observed.

Correlations of neutral and charged particles in 40Ar- 58Ni reaction at 77 MeV/u

The measurement of the two-particle correlation function for different particle species allows to obtain information about the development of the particle emission process: the space-time properties of emitting sources and the emission time sequence of different particles. The single-particle characteristics and two-particle correlation functions for neutral and charged particles registered in forward direction are used to determine that the heavy fragments (deuterons and tritons) are emitted in the first stage of the reaction (pre-equilibrium source) while the majority of neutrons and protons originates from the long-lived quasi-projectile. The emission time sequence of protons, neutrons and deuterons has been obtained from the analysis of non-identical particle correlation functions.

Studying spacetime structure of multi-strange baryon source using non-identical particle correlations

We present preliminary results on π–Ξ correlations in Au+Au collisions at = 200 GeV as measured by the STAR experiment at RHIC. The technique of spherical decomposition is used to access the emission asymmetry due to flow of multi-strange baryons and compare with theoretical calculations.

Non-identical particle correlations at 62 and 200 GeV at STAR

We report on STAR analyses of p − Λ , p ¯ − Λ ¯ , p − Λ ¯ , p ¯ − Λ , p − p ¯ and π − Ξ correlations in Au+Au collisions at s N N = 62 and 200 GeV. Measured source sizes in p ( p ¯ ) − Λ ( Λ ¯ ) and p − p ¯ are shown to be in qualitative agreement with flow expectations. Interaction potential between p − Λ ¯ , p ¯ − Λ ¯ was investigated by measuring scattering length, thus showing that correlation analyses in heavy-ion collisions can be used to study strong interaction potential between hadrons. We present also analyses of π − Ξ correlations addressing independently on previous measurements the issue of Ξ flow in heavy-ion collisions.

Correlation Functions: Getting into Shape

The ability to measure characteristics of source shapes using non-identical particle correlations is discussed. Both strong-interaction induced and Coulomb induced correlations are shown to provide sensitivity to source shapes. By decomposing correlation functions with spherical or Cartesian harmonics, details of the shapes can be especially well isolated.

Proton–Lambda Correlations in Au–Au Collisions at v{ NN __

The space-time evolution of the source of particles formed in the collision of nuclei can be studied through particle correlations. The STAR experiment is dedicated to study ultra-relativistic heavy ions collisions and allows to measure non-identical strange particle correlations. The source size can be extracted by studying $p-\Lambda$, $\bar{p}-\bar{\Lambda}$, $\bar{p}-\Lambda$ and $p-\bar{\Lambda}$ correlation functions. Strong interaction potential has been studied for these systems using an analytical model. Final State Interaction (FSI) parameters have been determined and has shown a significant annihilation process present in $\bar{p}-\Lambda$ and $p-\bar{\Lambda}$ systems not present in $p-\Lambda$ and $\bar{p}-\bar{\Lambda}$.

Inhomogeneous cellular automata modeling for mixed traffic with cars and motorcycles

This paper develops inhomogeneous cellular automata models to elucidate the interacting movements of cars and motorcycles in mixed traffic contexts. The car and motorcycle are represented by non-identical particle sizes that respectively occupy 6×2 and 2×1 cell units, each of which is 1.25×1.25 meters. Based on the field survey, we establish deterministic cellular automata (CA) rules to govern the particle movements in a two-dimensional space. The instantaneous positions and speeds for all particles are updated in parallel per second accordingly. The deterministic CA models have been validated by another set of field observed data. To account for the deviations of particles' maximum speeds, we further modify the models with stochastic CA rules. The relationships between flow, cell occupancy (a proxy of density) and speed under different traffic mixtures and road (lane) widths are then elaborated.

Non-Identical Particle Correlations in STAR

Non-identical particle correlations offer new methods of probing the dynamics of heavy-ion collision. In STAR we have performed a correlation analysis of pion-kaon and pion-proton systems for √sNN = 130 AGeV Au+Au collisions. The results show that average emission space-time points of pions, kaons and protons are not the same. These results are studied with the help of heavy-ion collision models. The asymmetries appear as a consequence of space-momentum correlations produced by transverse radial expansion of the system. The effects of emission time differences, coming from the decay of resonances are also investigated, and found to explain only part of the asymmetry.

Non-identical particle correlations in 130 and 200 A GeV collisions at STAR

STAR has performed correlation analyses of pion–kaon and pion–proton pairs for and and kaon–proton, proton–Lambda and pion–Cascade pairs for AuAu collisions . They show that average emission spacetime points of pions, kaons and protons are not the same. These asymmetries are interpreted as a consequence of transverse radial expansion of the system; emission time differences explain only part of the asymmetry. Therefore our measurements independently confirm the existence of transverse radial flow. Furthermore, correlations of strange hyperons are investigated by performing proton–Lambda and pion–Cascade analyses, giving estimates of source size at high mT. The strong interaction potential between (anti-)proton and lambda as well as kaon and proton is investigated.

The Reconstructed Final State of Au + Au Collisions from PHENIX and STAR Data at [ s ] 1/2 = 130 AGeV - Indication for Quark Deconfinement at RHIC

The final state of Au+Au collisions at √s=130 AGeV at RHIC has been reconstructed within the framework of the Buda-Lund hydrodynamical model, by performing a simultaneous fit to final data on twoparticle Bose-Einstein correlations of the STAR and PHENIX Collaboration, and final identified single-particle spectra as measured by the PHENIX Collaboration. The results indicate a strongly three dimensional expansion, with a four-velocity field that is almost a spherically symmetric Hubble flow. We find large transverse geometrical source sizes, R G=9.8±1.2 fm, relatively short mean freeze-out time, τ0=6.1±0.3 fm/c and a short duration of particle emission, Δτ=0.02±1.5 fm/c. Most strikingsly, we find an indication for a hot central part of the hydrodynamically evolving core, characterized by a central temperature T 0=202±13 MeV that is close to (or even above) the deconfinement temperature of the quark-hadron phase transition. The best fit indicates a cold surface temperature T s=110±16 MeV. When the possibility of the hot center is excluded, the confidence level of the fit decreases from 28.9% to 1.0%. Predictions are made for the rapidity dependence of the slope parameters and for the transverse mass depedence of the rapidity width of the single-particle spectra, and the transverse mass dependence of the non-identical particle correlations.

Non-identical particle correlation analysis as a probe of transverse flow

Non-identical two particle correlation functions probe asymmetries between the average space-time emission points of different particle species. The system collective expansion would produce such asymmetry because massive particles, such as protons, are on average more pushed towards the edge of the system, than lighter ones, i.e. pions. Measuring pion-kaon, pion-proton and kaon-proton correlation functions, using the STAR detector, we show that the data are consistent with the effect of transverse flow in Au Au collisions at S N N = 130 GeV.

Mid-rapidity multi-strange baryon production at √sNN = 130 GeV

We report preliminary results on production of multi-strange Ξ− and their anti-particles, +, at mid-rapidity in √sNN = 130 GeV Au + Au collisions from the STAR experiment. An exponential fit to the Ξ− transverse mass spectrum for the 14% most central collisions results in an inverse slope parameter T = 346 ± 7 MeV, an invariant yield dN/dy = 3.07 ± 0.13 (stat) and a non-identical particle ratio Ξ−/Λ = 0.244 ± 0.011. The multi-strange baryon production with respect to negative hadrons is found to be Ξ−/h− = 0.0122 ± 0.0006.

The contribution of orbiting to elastic total cross section

A simple formulation of orbiting is provided by using the Regge theory. A closed formula for the elastic total cross section is given, both for identical and non-identical particle collisions. It is shown that a single Regge pole can reproduce quantitatively an entire structure of orbiting resonances for a wide range of energy. This is supported by detailed calculation on the system H2-Kr, for which the total cross section has been measured. The resulting expressions are used to calculate explicitly the effect of velocity averaging of the total cross section.