Bring poaching water, salt and bay leaf to a gentle simmer. Add shrimp and poach for 3 to 4 minutes until opaque throughout and 145°F in the thickest pieces.
Transfer shrimp to the ice and cold bath water for 3 to 5 minutes until cold, then drain and pat thoroughly dry. Discard poaching liquid and bay leaf.
Chop shrimp into 1/2-inch pieces. Fold with mayonnaise, celery, tarragon, lemon juice and pepper, then cover and refrigerate for 20 minutes until thoroughly cold.
Meanwhile, open rolls gently without cutting through their joined bottoms and butter the inside faces. Toast buttered faces in a skillet over medium heat for 2 to 3 minutes, then cool on a rack for 10 minutes.
Divide cold shrimp salad among the cooled rolls. Serve immediately or refrigerate at 40°F or below, transporting with ice packs; prep time includes cooling and chilling.