  We initiate a study of asymptotic detector operators in weakly-coupled field
theories. These operators describe measurements that can be performed at future
null infinity in a collider experiment. In a conformal theory they can be
identified with light-ray operators, and thus have a direct relation to the
spectrum of the theory. After a general discussion of the underlying physical
picture, we show how infrared divergences of general detector operators can be
renormalized in perturbation theory, and how they give rise to detector
anomalous dimensions. We discuss in detail how this renormalization can be
performed at the intersections of the Regge trajectories where non-trivial
mixing occurs, which is related to the poles in anomalous dimensions at special
values of spin. Finally, we discuss novel horizontal trajectories in scalar
theories and show how they contribute to correlation functions. Our
calculations are done in the example of $\phi^4$ theory in $d=4-\epsilon$
dimensions, but the methods are applicable more broadly. At the Wilson-Fisher
fixed point our results include an explicit expression for the Pomeron
light-ray operator at two loops, as well as a prediction for the value of the
Regge intercept at five loops.
