Bimodality in spectator fragmentation

The fluctuations of the largest fragment charge of a partition and of the charge asymmetries of the two or three largest fragments in spectator decays following 197Au + 197Au collisions at 1000 MeV per nucleon are investigated. The observed bimodal distributions at specific values of the sorting variable Z_bound exhibit features known from percolation theory where they appear as finite-size effects. The underlying configurational fluctuations seem generic for fragmentation processes in small systems.
Comment: 10 pages, 7 figures, to appear in Proceedings of the XLVth International Winter Meeting on Nuclear Physics}, Bormio, Italy, January 2007 (one reference added after submission)