  In this paper we study stationary last passage percolation (LPP) in
half-space geometry. We determine the limiting distribution of the last passage
time in a critical window close to the origin. The result is a new
two-parameter family of distributions: one parameter for the strength of the
diagonal bounding the half-space (strength of the source at the origin in the
equivalent TASEP language) and the other for the distance of the point of
observation from the origin. It should be compared with the one-parameter
family giving the Baik--Rains distributions for full-space geometry. We finally
show that far enough away from the characteristic line, our distributions
indeed converge to the Baik--Rains family. We derive our results using a
related integrable model having Pfaffian structure together with careful
analytic continuation and steepest descent analysis.
