Sources In Heavy-ion Collisions Research Articles

Kaon Femtoscopy with Lévy-Stable Sources from sNN=200 GeV Au+Au Collisions at RHIC

Femtoscopy has the capacity to probe the space-time geometry of the particle-emitting source in heavy-ion collisions. In particular, femtoscopy of like-sign kaon pairs may shed light on the origin of non-Gaussianity of the spatial emission probability density. The momentum correlations between like-sign kaon pairs are measured in data recorded by the STAR experiment, from sNN=200 GeV Au+Au collisions at RHIC, BNL. Preliminary results hint at the possible existence of non-Gaussian, Lévy-stable sources, with the likely presence of an anomalous diffusion process in the signal for the identically charged kaon pairs so produced. More statistically significant studies at lower centre-of-mass energies may contribute to the search for the critical end point of QCD.

Strange hadron correlations in heavy-ion collisions at RHIC energies and below

Geometry and dynamics of the particle-emitting source in heavy-ion collisions can be inferred via the femtoscopy method. Two-particle correlations at small relative momentum exploit Quantum Statistics and the Final State Interactions (Coulomb and strong), which allow one to study the space-time characteristics of the source of the order of 10−15 m and 10−23 s. Femtoscopic measurements allow one also to study FSI, especially the strong one, which is unknown for many two-particle systems. The RHIC program covers a significant part of the QCD phase diagram using collisions of Au nuclei for several beam energies from 7.7 to 200 GeV for which baryon-rich region is studied via femtoscopy. These measurements complement those obtained from AGS, SPS, and SIS experiments. Strange hadron measurements together with nonstrange ones provide complementary information about source characteristics. Strangeness is a significant observable for many regimes of collision energies providing a complete view of strangeness production in heavy-ion collisions. These proceedings shows the femtoscopic measurements of various strange particle combinations at different collision energies and centralities of the collision.

Shape Analysis of HBT Correlations at STAR

To study the nature of the quark-hadron phase transition, it is important to investigate the space-time structure of the hadron-emitting source in heavy-ion collisions. Measurements of HBT correlations have proven to be a powerful tool to gain information about the source. In these proceedings, we report the current status of the analysis of source parameters obtained from L\'evy fits to the measured one-dimensional two-pion correlation functions in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.

Electromagnetic fields from quantum sources in heavy-ion collisions

We compute the electromagnetic field created by an ultrarelativistic charged particle in vacuum at distances comparable to the particle Compton wavelength. The wave function of the particle is governed by the Klein-Gordon equation, for a scalar particle, or the Dirac equation, for a spin-half particle. The produced electromagnetic field is essentially different in magnitude and direction from the Coulomb field, induced by a classical point charge, due to the quantum diffusion effect. Thus, a realistic computation of the electromagnetic field produced in heavy-ion collisions must be based upon the full quantum treatment of the valence quarks.

Classical electromagnetic fields from quantum sources in heavy-ion collisions

Electromagnetic fields are generated in high energy nuclear collisions by spectator valence protons. These fields are traditionally computed by integrating the Maxwell equations with point sources. One might expect that such an approach is valid at distances much larger than the proton size and thus such a classical approach should work well for almost the entire interaction region in the case of heavy nuclei. We argue that, in fact, the contrary is true: due to the quantum diffusion of the proton wave function, the classical approximation breaks down at distances of the order of the system size. We compute the electromagnetic field created by a charged particle described initially as a Gaussian wave packet of width 1 fm and evolving in vacuum according to the Klein–Gordon equation. We completely neglect the medium effects. We show that the dynamics, magnitude and even sign of the electromagnetic field created by classical and quantum sources are different.

PHENIX Results on Bose--Einstein Correlation Functions

Measurement of Bose-Einstein or HBT correlations of identified charged particles provide insight into the space-time structure of particle emitting sources in heavy-ion collisions. In this paper we present the latest results from the RHIC PHENIX experiment on such measurements.

Two- and three-pion quantum statistics correlations in Pb-Pb collisions atsNN=2.76 TeV at the CERN Large Hadron Collider

Correlations induced by quantum statistics are sensitive to the spatio-temporal extent as well as dynamics of particle emitting sources in heavy-ion collisions. In addition, such correlations can be used to search for the presence of a coherent component of pion production. Two and three-pion correlations of same and mixed-charge are measured at low relative momentum to estimate the coherent fraction of charged pions in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV at the LHC with ALICE. The genuine three-pion quantum statistics correlation is found to be suppressed relative to the two-pion correlation based on the assumption of fully chaotic pion emission. The suppression is observed to decrease with triplet momentum. The observed suppression at low triplet momentum may correspond to a coherent fraction in charged pion emission of 23% $\pm$ 8%.

Particle production sources at LHC energies

Particle production sources at RHIC and LHC energies are investigated in pseudorapidity space. A nonequilibrium-statistical relativistic diffusion model with three sources is applied to the analysis of charged-hadron distributions in AuAu collisions at RHIC energies, in PbPb collisions at the current LHC energy of 2.76 TeV, in pPb at 5.02 TeV, and in pp. The size of the midrapidity source relative to the fragmentation sources in heavy-ion collisions is investigated as function of incident energy. At LHC energies, the midrapidity value is mostly determined by particle production from gluon–gluon collisions.

Two-Pion Interferometry for the Granular Source in Heavy Ion Collisions at LHC Energies

The space-time characters of the pion-emitting sources produced in the heavy ion collisions at the Large Hadron Collider (LHC) energies are investigated in a granular source model of quark-gluon plasma droplets. The results of two-pion interferometry indicate that the longitudinal interferometry radius is sensitive to the initial breakup time of the system. For a larger breakup time the values of the longitudinal interferometry radius for the LHC source are larger than that of the source produced in the collisions at the Relativistic Heavy Ion Collider's (RHIC) top energy. However, the values of the longitudinal radius are smaller if the source fragments at a smaller breakup time with a higher initial temperature of the droplets. The values of the transverse interferometry radius in the “side" direction for the LHC sources are larger than those for the RHIC source. The imaging analyses for the characteristic quantities of the granular sources are consistent with the interferometry radii.

Interferometry imaging for the evolving source in heavy ion collisions at HIRFL-CSR energy

Imaging analysis of two-pion interferometry is performed for an evolving particle-emitting source in heavy ion collisions at HIRFL-CSR energy. The source evolution is described by the relativistic hydrodynamics in (2+1) dimensions. The model-independent characteristic quantities of the source are investigated and compared with the interferometry results obtained by the usual Gaussian formula fit. It is found that the first-order source function moments can describe the source sizes. The ratio of the normalized standard deviation σ̃ to the first-order moment R̃, σ̃/R̃, is sensitive to the shape of the source function.

Transport model study of the [formula omitted]-scaling for Λ, K, and π HBT-correlations

Based on the microscopic transport model UrQMD in which hadronic and string degrees of freedom are employed, the HBT parameters in the longitudinal co-moving system are investigated for charged pion and kaon, and Λ sources in heavy ion collisions (HICs) at SPS and RHIC energies. In the Cascade mode, RO and the RL at high SPS and RHIC energies do not follow the mT-scaling, however, after considering a soft equation of state with momentum dependence (SM-EoS) for formed baryons and a density-dependent Skyrme-like potential for “pre-formed” particles, the HBT radii of pions and kaons and even those of Λs with large transverse momenta follow the mT-scaling function R=3/mT fairly well.

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1–2A GeV

Angular distributions of pions and kaons produced in heavy ion collisions at the low-energy end of high energies (1–2A GeV) have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.

Correlation search for coherent pion emission in heavy ion collisions

The methods allowing to extract the coherent component of pion emission conditioned by the formation of a quasi-classical pion source in heavy ion collisions are suggested. They exploit a nontrivial modification of the quantum statistical and final state interaction effects on the correlation functions of like and unlike pions in the presence of the coherent radiation. The extraction of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation functions and single--pion spectra is discussed in detail for large expanding systems produced in ultra-relativistic heavy ion collisions.

Reconstructing the source in heavy ion collisions from particle interferometry

The preliminary CERN SPS NA 49 Pb+Pb 158 GeV / A one- and two-particle h −-spectra at mid-rapidity are consistent with a source of temperature T ≈ 130 MeV, lifetime τ 0 ≈ 9fm/c, transverse flow η f ≈ 0.35, and a transverse geometric size which is twice as large as the cold Pb nucleus.

Comment on “Measurement of the space-time extent of the hard-photon emitting source in heavy-ion collisions at 100 MeV/nucleon”

In a recent paper [Phys. Rev. C 55, 2521 (1997)] two-photon coincidences were studied for three nuclear reactions. From a correlation analysis, the authors evaluated the size and lifetime of the emitting source. In this Comment we correct some arguments used in the comparison of the extracted and estimated sizes, and show that the parametrization of the relative-momentum correlations leads to values which should not be assigned to the space-time extent of the source.

Reply to “Comment on ‘Measurement of the space-time extent of the hard-photon emitting source in heavy-ion collisions at 100 MeV/nucleon’ ”

Reply to “Comment on ‘Measurement of the space-time extent of the hard-photon emitting source in heavy-ion collisions at 100 MeV/nucleon’ ”

Measurement of the space-time extent of the hard-photon emitting source in heavy-ion collisions at 100 MeV/nucleon

The correlation between the couples of high-energy photons ${(E}_{\ensuremath{\gamma}}g30\mathrm{MeV})$ detected in the reactions induced by a ${}^{36}\mathrm{Ar}$ beam on ${}^{27}\mathrm{Al},$ ${}^{112}\mathrm{Sn},$ and ${}^{197}\mathrm{Au}$ targets at 95 MeV/nucleon has been analyzed with the intensity interferometry technique. Both the size and lifetime of the emitting source have been quantitatively evaluated. Results support the nucleon-nucleon picture as the dominant hard-photon production mechanism.

Multiplicity Dependence of Pion Source Size in Heavy Ion Collisions

HBT interferometry is a well known technique to study the space-time extent of the particle source in heavy ion collisions. The NA44 experiment measures one and two particle spectra of identified pions, kaons and protons around mid-rapidity produced in heavy ion collision at the CERN SPS. We present the relation between charged multiplicity density and the HBT radius parameters in S + Pb collisions at 200 A GeV and Pb + Pb collisions at 158 A GeV. The HBT radius parameter increases as a function of charged multiplicity density in Pb + Pb collisions in a similar way to that found previously in S + Pb collisions. We will discuss what we can learn about the condition at freeze-out using these experimental results.

Stopped Delta -matter source in heavy-ion collisions at 10 GeV/nucleon?

We predict the formation of highly dense baryon-rich resonance matter in Au+Au collisions at AGS energies. The final pion yields show observable signs for resonance matter. The Delta(1232) resonance is predicted to be the dominant source for pions of small transverse momenta. Rescattering effects -- consecutive excitation and deexcitation of Deltas -- lead to a long apparent lifetime (> 10 fm/c) and rather large volumina (several 100 fm^3) of the Delta-matter state. Heavier baryon resonances prove to be crucial for reaction dynamics and particle production at AGS.

Antinucleon sources in heavy-ion collisions

As recently measured in relativistic heavy-ion collisions, the antideuteron formation rate, which is the ratio of the antideuteron production cross section to the antiproton cross section squared at the same momentum per nucleon, is substantially smaller than the formation rate of deuterons. This happens because the shape of the antinucleon source is different from the nucleon one. In the case of baryon-rich sources, the nucleons are emitted from the whole source volume while antinucleons are emitted predominantly from the surface due to antinucleon absorption in the baryon environment.