Regular Article – Experimental Physics
Femtoscopy in p+p vs. heavy ion collisions in STAR
Department of Physics, The Ohio State University, Columbus, OH, 43210, USA
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Published online: 28 November 2006
The geometric substructure of the particle-emitting source has been characterized via two-particle interferometry by the STAR collaboration for several energies and colliding systems at RHIC. In heavy ion collisions the mT dependence of femtoscopic radii has been observed for all particle types by several experiments at different collision energies. This dependence has been thought to arise from space-momentum correlations generated by collective flow. On the other hand, there are several reports of a similar mT dependence by experiments measuring elementary particle collisions. Here, quite different physical mechanisms – including resonances, strings, and uncertainty arguments – have been proposed to explain the dependence. Determining the differences or similarities in the space-time physics driving the signal in heavy ion versus p+p collisions requires a direct comparison of mT dependence of the radii. Such a comparison has, until now, been sorely lacking. STAR data allow, for the first time, such a direct comparison between A+A, d+A, and p+p collisions, at the same energy, measured in the same detector, and using the same analysis techniques. Surprisingly, our preliminary results indicate an mT-independent scaling of the femtoscopic radii with overall system size. Possible physics implications of these observations will be discussed, and the importance of long-range non-femtoscopic correlations for low multiplicity collisions will be emphasized.
© Springer-Verlag Berlin Heidelberg, 2007