The correlations of identical pions in multibody production

The identical quanta correlations give an information on the spatial and time structure of the production reactions. Their dependence on the multiplicity and average particle energy is estimated and compared with available data.     

Note on Bose-Einstein correlations of three pions in symmetric heavy-ion interactions at 650 a MeV

In a recent article published in this journal it is stated that a specific three-pion effect is found in an experiment studying Au+Au collisions. The aim of this note is to show that these new data are compatible with two-pion effects leaving no room for a specific three-pion effect. This is in accordance with three-pion interferometry results from pp and e⁺ e^? collisions at a high energy.     

Bose-Einstein correlations for pions produced inp p collisions at 360 GeV/c

Zeitschrift für Physik C Particles and Fields - Correlations among identically charged pions were measured for pions produced inp p collisions at 360 GeV/c using the EHS spectrometer. The...     

Bose-Einstein correlations of three charged pions in hadronic Z^{\bf 0} decays

Bose-Einstein Correlations (BEC) of three identical charged pions were studied in hadronic decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of and a strength of . The Coulomb correction was found to increase the value by 9% and to reduce by 6%. The measured corresponds to a value of when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed. Received: 7 May 1998 / Published online: 12 August 1998     

An event mixing technique for Bose-Einstein correlations of two pions in photoproduction around 1 GeV

We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.     

Condensates and Bose-Einstein correlations

We discuss the conditions under which Bose-Einstein correlation can be used to determine the presence of condensates. One starts from the fact that any condensate is a coherent state and uses then the formalism of quantum optics. The case of final state interactions is considered explicitly in a Landau-Ginzburg type approach as used in laser physics. By applying a mean field Hartree approximation for the many mode problem we find that the second order correlation function for identical bosons $\text{C}{}_2\text{(}\text{p}{}_1\text{?}\text{p}{}_2\text{=0)}$ does effectively not depend on the phenomenological coupling constant g and thus C₂(0) can be used to determine the amount of coherence and hence the existence of condensates. On the other hand $\text{C}{}_2\text{(}\text{p}{}_1\text{?}\text{p}{}_2\text{≠0)}$ does depend on g and therefore its measurement provides information about g. The implications of these findings for the determination of the size and lifetime of the source á la Hanbury-Brown-Twiss are discussed. Our conclusions apply both to condensates in nuclear (pion condensates, alpha and deuteron condensates) and hadronic matter.     

Coherence influence on the Bose-Einstein correlations

Two-particle correlations for both like and unlike pion pars are considered using the method of ensemble of sources with partially random phases. The dependence of both the interferometric source size and the coherence parameter on the source size and on the meansquared momentum of the emitted pions is found.     

Bose-Einstein correlations and isospin

Bose-Einstein correlations between pions are analysed in terms of isospin. The lack of Bose-Einstein correlation between π⁺ and π⁰ is explicitly demonstrated.     

Bose-Einstein correlations of pion wavepackets

A wavepacket model for a system of free pions, which takes into account the full permutation symmetry of the wavefunction and which is suitable for any phase space parametrization is developed. The properties of the resulting mixed ensembles and the two-particle correlation function are discussed. A physical interpretation of the chaoticity λ as localization of the pions in the source is presented. Two techniques to generate test-particles, which satisfy the probability densities of the wavepacket state, are studied:

1. A Monte Carlo procedure in momentum space based on the standard Metropolis technique.
2. A molecular dynamic procedure using Bohm’s quantum theory of motion. In order to reduce the numerical complexity, the separation of the wavefunction into momentum space clusters is discussed. In this context the influence of an unauthorized factorization of the state, i. e. the omission of interference terms, is investigated. It is shown that the correlation radius remains almost uneffected, but the chaoticity parameter decreases substantially. A similar effect is observed in systems with high multiplicities, where the omission of higher order corrections in the analysis of two-particle correlations causes a reduction of the chaoticity and the radius. The approximative treatment of the Coulomb interaction between pions and the source is investigated. The results suggest that Coulomb effects on the correlation radii are not symmetric for pion pairs of different charges. For (π^?,π^?) pairs the radius, integrated over the whole momentum spectrum, increases substantially, while for (π⁺,π⁺) pairs the radius remains almost unchanged.

     

Source parameters deduced from Bose-Einstein correlations of two and three soft pions in symmetric heavy-ion interactions at 650 A MeV

The analysis of Bose-Einstein correlations for systems of two and three low-momentum pions in interactions of Au+Au and Nb+Nb at 650 A MeV kinetic energy are presented. The data were taken with the Plastic Ball spectrometer. The pion-emitting source sizes obtained from specific three-pion correlations are significantly smaller than those extracted from two-pion correlations. The dependence of the source parameters on the multiplicity of produced pions was examined. The low-p _t pions are emitted from a larger region than the high-p _t ones.     

Finite-temperature Bose-Einstein distribution functions of identical particles

We study the evolution properties of propagating identical particles produced at a finite temperature in a randomly distributed environment. The lower bound on the spacetime size of the multiparticle production region and the correlation chaoticity are derived.     

Bose-Einstein correlations and color strings

It is shown that correlations between like-sign bosons (the “Bose-Einstein effect”) arise naturally in string fragmentation models for e⁺e⁻ annihilation. Via the area dependence of Wilson loop integrals, the correlation length in momentum space can be related to the string tension.     

Bose-Einstein correlations in thermal field theory

Two-particle correlation functions are calculated for bosons emitted from a localized thermal source (the “glow” of a “hot spot”). In contrast to existing work, non-equilibrium effects up to first order in gradients of the particle distribution function are taken into account. The spectral width of the bosons is shown to be an important quantity: if it is too small, they do not equilibrate locally and therefore strongly increase the measured correlation radius.     

Bose-Einstein correlations in the Lund model

By providing the Lund model fragmentation process with a quantum mechanical framework we extend the results of Andersson and Hofmann [Phys. Lett. B 169 (1986) 364] to situations where there are very many identical bosons. We investigate the features of the weight distributions in some detail and in particular exhibit three-particle BE correlations, the influence on the ϱ-spectrum and the difference between charged and neutral pion correlations.     

Multiparticle azimuthal correlations of negative pions in nucleus-nucleus collisions

Multiparticle azimuthal correlations of ?? ^? mesons have been studied in dC, HeC, CC, CNe, MgMg, (d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis ?? ^? meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile (A _P ) and target (A _T ) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results.