Abstract
We investigate identical pion HBT intensity interferometry in central Au+Au collisions at 1.23A GeV. High-statistics π−π− and π+π+ data are measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinally comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy.
Highlights
We investigate identical pion HBT intensity interferometry in central Au + Au collisions at 1.23 A GeV
The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy
Intensity interferometry generally does not yield the proper source size, but rather an effective “length of homogeneity” [1]. It measures source regions in which particle pairs are close in momentum, so that they are correlated as a consequence of their quantum statistics or due to their two-body interaction
Summary
The constructed π 0π 0 correlation radii are derived from cubic spline interpolations of the kt dependence of both the corresponding experimental π −π − and π +π + data This interpolation is necessary because – as result of different detector acceptances – the charged pion pairs exhibit slightly different average transverse momenta, even though they are measured in identical kt intervals. Note that the charge splitting of the source radii was early predicted by Barz [31,32] who investigated the combined effects of nuclear Coulomb field, radial flow, and opaqueness on two-pion correlations for a large collision system such as Au + Au in the 1 A GeV energy regime. In accordance with the overall smooth trend within 2 σ .
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