Where can I find a specific reference to the minimum length of the blade that may be used for ritual slaughter of cattle?
I thought that this was in the Shulchan Aruch (Yoreh De’ah), but cannot find it.
I think that the minimum length is twice the width of the animal’s neck, but do need the reference.
See Yoreh Deah Siman 8 and the commentaries there. The actual size is smaller, for technical reasons we use the size you described, see ibid.