Vertex-primitive s-arc-transitive digraphs admitting a Suzuki or Ree group

The investigation of s-arc-transitivity of digraphs can be dated back to 1989 when the third author showed that s can be arbitrarily large if the action on vertices is imprimitive. However, the situation is completely different when the digraph is vertexprimitive and not a directed cycle. In 2017 the second author, Li and Xia constructed the first infinite family of G-vertex-primitive 2-arc-transitive examples, and asked if there is an upper bound on s for G-vertex-primitive s-arc-transitive digraphs that are not directed cycles. In 2018 the second author and Xia showed that if there is a largest such value of s then it will occur when G is almost simple. So far it has been shown that s <= 2 for almost simple groups whose socle is an alternating group or a projective special linear group. The contribution of this paper is to prove that s <= 1 in the case of the Suzuki groups and the small Ree groups. We give constructions with s = 1 to show that the bound is sharp.