# ar X iv : n uc l - th / 9 80 20 74 v 1 2 4 Fe b 19 98 Partial U A ( 1 ) Restoration from Bose - Einstein Correlations

• Published 1998

#### Abstract

The effective intercept parameter of the two-pion Bose-Einstein Correlation function, λ∗, is found to be sensitive to partial restoration of UA(1) symmetry in ultra-relativistic nuclear collisions. An increase in the yield of the η meson, proposed earlier as a signal of partial UA(1) restoration, is shown to create a “hole” in the low pt region of λ∗. A comparison with NA44 data [1] for central S+Pb collisions at 200 AGeV is made and implications for forthcoming heavy ion experiments are discussed. Introduction: Intensity interferometry is a useful method for studying the space-time geometry of high energy nucleus-nucleus collisions and elementary particle reactions (for recent reviews, see ref [2,3]). In particular, pion interferometry has proved useful in studying the space-time dependence of pion emission as was first shown experimentally by Goldhaber, Goldhaber, Lee and Pais [4]. The method of intensity interferometry, known also as Hanbury-Brown-Twiss (HBT) correlations, was introduced by Hanbury-Brown and Twiss [5] in measuring the angular diameters of main sequence distant stars. The purpose of this letter is show that pion interferometry can be used to detect the axial UA(1) restoration and the related increase of the η production. As was shown in several papers [6,7], at incident beam energies of 200 AGeV at the CERN 1 SPS, the space-time structure of pion emission in high energy nucleus-nucleus collisions can be separated into two separate regions: the core and the halo. The pions which are emitted from the core or central region consist of two types. The first type is produced from a direct production mechanism such as the hadronization of wounded string-like nucleons in the collision region. These pions re-scatter as they flow outward with a re-scattering time on the order of 1 fm/c. The second type is produced from the decays of short-lived hadronic resonances such as the ρ, N, ∆ and K, whose decay time is also on the order of 1-2 fm/c. This core region is resolvable by Bose-Einstein correlation (BEC) measurements. The halo region, however, consists of the decay of long-lived hadronic resonances such as the ω, η, η and K S whose lifetime is greater than 20 fm/c. This halo region is not resolvable by BEC measurements. However, as will be summarized below, this region still affects the Bose-Einstein Correlation function. In recent papers [8,9], it was argued that the partial restoration of UA(1) symmetry of QCD and related decrease of the η mass [10–12], in regions of sufficiently hot and dense matter should manifest itself in the increased production of η mesons. Estimates of ref [8] show that the corresponding production cross section of the η should be enhanced by a factor of 3 up to 50 relative to that for p+p collisions. Let us now show that the effective intercept parameter, λ∗, can be written in terms of the one-particle invariant momentum distributions of the core and halo pions and thus is sensitive to the abundance of the long-lived hadronic resonances such as the η. Qualitative Estimate: The effective intercept parameter, λ∗, can be written in terms of one-particle invariant momentum distributions [6,7]. To see this, consider the two-particle Bose-Einstein correlation function. The two-particle Bose-Einstein correlation function is defined as C(K,∆k) = N2(p1,p2) N1(p1)N1(p2) , (1) where the inclusive n-particle invariant momentum distribution is given as Nn(p1, ...,pn) = 1 σin E1...En dσ dp1...dpn , (2)

### Cite this paper

@inproceedings{Vance1998arXI, title={ar X iv : n uc l - th / 9 80 20 74 v 1 2 4 Fe b 19 98 Partial U A ( 1 ) Restoration from Bose - Einstein Correlations}, author={Stephen E. Vance and Tam{\'a}s Cs{\"{o}rgő and Dmitri E. Kharzeev}, year={1998} }