Transverse momentum fluctuations can be understood as resulting from clustering of strings or partons. Data allows to distinguish clustering without percolation, from clustering with percolation. Percolation is clearly favored by data.
@article{arxiv.hep-ph/0308011,
title = {Transverse Momentum Fluctuations from Clustering and Percolation of Strings},
author = {J. Dias de Deus and A. Rodrigues},
journal= {arXiv preprint arXiv:hep-ph/0308011},
year = {2007}
}