Non-identical Particle Correlations Research Articles

Pion–kaon femtoscopy and the lifetime of the hadronic phase in Pb−Pb collisions at [formula omitted] TeV

In this paper, the first femtoscopic analysis of pion–kaon correlations at the LHC is reported. The analysis was performed on the Pb–Pb collision data at sNN=2.76 TeV recorded with the ALICE detector. The non-identical particle correlations probe the spatio-temporal separation between sources of different particle species as well as the average source size of the emitting system. The sizes of the pion and kaon sources increase with centrality, and pions are emitted closer to the centre of the system and/or later than kaons. This is naturally expected in a system with strong radial flow and is qualitatively reproduced by hydrodynamic models. ALICE data on pion–kaon emission asymmetry are consistent with (3+1)-dimensional viscous hydrodynamics coupled to a statistical hadronisation model, resonance propagation, and decay code THERMINATOR 2 calculation, with an additional time delay between 1 and 2 fm/c for kaons. The delay can be interpreted as evidence for a significant hadronic rescattering phase in heavy-ion collisions at the LHC.

Effects of Ptot gates and velocity gates on light-particle momentum correlation in intermediate-energy heavy-ion collisions

Momentum correlation functions at small relative momenta are calculated for light particles $\left(n, p, d, t\right)$ emitted from $^{197}$Au + $^{197}$Au collisions at different impact parameters and beam energies within the framework of the isospin-dependent quantum molecular dynamics model complemented by the $Lednick\acute{y}$ and $Lyuboshitz$ analytical method. We first make sure our model is able to reproduce the FOPI data of proton-proton momentum correlation in a wide energy range from 0.4$A$ GeV to 1.5$A$ GeV. Then we explore more physics insights through the emission times and momentum correlations among different light particles. The specific emphasize is the effects of total pair momentum among different light particles, impact parameters and in-medium nucleon-nucleon cross section. Both two-deuteron and two-triton correlation functions are anti-correlation due to the final state interaction, and they are affected by in-medium nucleon-nucleon cross section for the higher total momentum of the particle pairs, but not for the lower ones. In addition, impact parameter and in-medium nucleon-nucleon cross section dependences of the emission source radii are extracted by fitting the momentum correlation functions. The results indicate that momentum correlation functions gating with total pair momentum is stronger for the smaller in-medium nucleon-nucleon cross section factor $\left(\eta\right)$ or impact parameter $\left(b\right)$. Non-identical particle correlations ($np, pd, pt, $ and $dt$) are also investigated by the velocity-gated correlation functions which can give information of the particles' emission sequence, and the result indicates that heavier ones $\left(deuteron/triton\right)$ are, one the average, emitted earlier than protons, in the small relative momentum region.

Pion-kaon femtoscopy in Au+Au collisions at STAR

In non-identical particle correlations, e.g. pion-kaon femtoscopy, one can obtain information about source size and asymmetry in emission processes of pions and kaons. Such asymmetry give us knowledge of which type of particles is emitted first/second and/or from which region of the source. The studies of non-identical particle femtoscopy for Beam Energy Scan energies give us the opportunity to study how the source size and asymmetry in particle emission depend on the initial conditions of the collision. It also allows one to examine these parameters in the vicinity of the theoretical critical point. In these proceedings, we present STAR results of pion-kaon femtoscopy at mid-rapidity in Au+Au collisions at = 7.7, 19.6 and 39 GeV.

Pion-kaon femtoscopy in Au+Au collisions at STAR

Femtoscopy analysis allows us to extract information about the properties of particle emission source created after collision. From HBT of two correlated pions one can calculate source sizes; in addition, from the non-identical particle correlations, e.g. pion-kaon femtoscopy, one can obtain information not only about source sizes but the asymmetry in the emission processes of particles of different types as well. Such asymmetry gives knowledge of which kind of particles are emitted first/second and/or from which region of the source. The studies of non-identical particle femtoscopy for different collision energies gives us the opportunity to study how the source size and asymmetry in particle emission depend on the initial conditions of the collision. In these proceedings, we will present STAR results of pion-kaon femtoscopy at mid-rapidity in Au + Au collisions from the Beam Energy Scan program.

Prediction of non-identical particle correlations for the Beam Energy Scan program

Femtoscopy of two non-identical particles in heavy ion collisions enables one to study the space-time asymmetry in the particle's emission process. Theoretical studies based on EPOS model performed for collision energies from the Beam Energy Scan program in STAR allow us to investigate the dependence of source sizes and dynamics effects. Obtained information will enable us to predict the collective behaviour of femtoscopic particle's source.

Plans for correlation studies for BES program at RHIC

We present an overview of the main concepts concerning correlation studies for the Beam Energy Scan Program at STAR. QGP signatures at higher RHIC energies are the most obvious example of the creation of a new state of matter. In order to learn more about the transition to this state and to find a possible location of a critical point between a first-order transition and cross-over area, a new program dedicated to such analyses is formulated. Correlation studies are one of the most important obervables of the scanning of unknown region of the phase diagram. Measurements of elliptic flow, local parity violation in strong interactions, azimuthally-sensitive correlations as well as two-proton femtoscopy and nonidentical particle correlations are discussed in this paper.

Nonidentical-particle femtoscopy atsNN=200GeV in hydrodynamics with statistical hadronization

Non-identical particle femtoscopy probes not only the size of the emitting system, but also the emission asymmetries between particles of different mass, which are intimately related with the collective behavior of matter. We apply the technique to the simulations from the {\tt THERMINATOR}+Lhyquid model of the heavy-ion collisions at sqrt{s_{NN}}=200 AGeV. We present predictions for all common pair combinations and discuss their interpretation. Emphasis is put on extracting unique information about collective behavior of matter from the non-identical particle correlations and understanding the role of particles coming from decays of hadronic resonances. We also present, in detail, the technical aspects of the non-identical particle femtoscopy technique applied to data from the heavy-ion collisions. We list the sources of systematic errors coming from the method itself and the usual assumptions. We describe robust analysis methods and discuss their limitations.

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.

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.

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 $\bar{p}-\bar{\Lambda}$.

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.