Multidimensional HBT correlations in pp collisions at [formula].

We analyse second moments R2 of like-sign pion pairs in the two-dimensional (qL,qT) and three-dimensional (qO,qS,qL) 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 two-component 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. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]