The new particle, called "Xi_b^0", fits a hole in the group representation graph of ground-state baryons with J=1/2. You can see it in the graph on the right. Of all states in the middle level (ones containing one bottom quark) only the Xi_b^0 was still missing. By the way: none of the baryons of the top level have yet been observed.
I will add some information in this same post in a while, but I wish to wait for Pat Lukens' seminar before I do. You can follow it live at this site.
In the meantime, let me also mention that b-baryons are hot in CDF these days: a new paper just released in the arxiv describes the observation of a flavour-changing neutral current decay of lambda_b baryons (the one in black in the graph above), which is observed to decay into lambda baryons (then in turn producing a pion and a proton) and a pair of muons, with a significance of 5.8 standard deviations. Please get the paper here. I will blog about that result too, soon.