Multidimensional HBT correlations in pp̄ collisions at s = 630 GeV

Abstract

We analyse second moments R 2 of like-sign pion pairs in the two-dimensional (q L , q T ) and three-dimensional (q O , q S , q L ) decompositions of the three-momentum difference. Conventional fit parametrisations such as gaussian, exponential, power-law and Edgeworth fail miserably, while more elaborate ones such as Lévy do well but fail to yield a unique best-fit solution. A twocomponent model using a hard cut to separate small-and large-scale parts appears possible but not compelling. In all cases, the data exhibits a strong and hitherto unexplained peak at small momentum differences which exceeds current fits.

The Shape of the Correlation Function

“…It is therefore important to take note of alternatives to the standard Gaussian parameterization which have been proposed in the literature. Examples include exponential forms [15,16], various types of power laws [19], Edgeworth expansions [18,20], and even mixtures of exponentials and Gaussians [17]. Another popular, somewhat more general form is the Lévy (or Lévy-stable) distribution, which has been explored in connection with sensitivity to enhanced fluctuations near a QCD critical point [4,5].…”