With the upcoming turn-on of the Large Hadron Collider (LHC), high energy physics is on the verge of entering its most exciting period in a generation. How will we reconstruct the fundamental theory of the electroweak scale from LHC data? The major discoveries at hadron colliders in the last thirty years—those of the W and Z bosons and the top quark—were of particles whose properties were exactly predicted by the Standard Model (for the W and Z) or characterized by a single unknown parameter (m_t for the top quark). By contrast, the LHC is so exciting precisely because the answer to the question—what will we see?—has never been more uncertain.

The questions about new physics that must be answered first are therefore big-picture, structural ones: What kinds of particles are being made with what sorts of rates? What pattern of decays do they exhibit? Only with this information can we tackle the fundamental questions: What new physical principles are being manifested at the TeV scale? Is nature supersymmetric? Is the electroweak scale natural? Given the tremendous range of possibilities, a coherent strategy for going from data to a still-unknown theory is necessary.

We propose and develop such a strategy, using On-Shell Effective Theories (OSETs) as an intermediary between LHC data and the underlying Lagrangian. An OSET is a model-independent characterization of new-physics processes in terms of their dominant kinematic structure—the masses, production cross sections, and decay modes of candidate new particles. The success of this approach relies on three interrelated facts that we establish in our preprint:

1. An OSET furnishes a simple, consistent parametrization of any particle model of new physics.
2. OSETs have few parameters, all with transparent physical meaning; these parameters can be scanned efficiently through re-weighting of post-detector-simulated Monte Carlo. By contrast, the relation between Lagrangian parameters and observables is often obscure, and Monte Carlo must be generated separately for every point in the Lagrangian parameter space. Thus, OSETs can be simulated more rapidly than Lagrangians, and are more readily interpreted.
3. An OSET concisely describes many distinct event topologies with correlated rates. Therefore, simple observables and correlations between them place powerful constraints on OSET descriptions of new-physics signals; an OSET in turn strongly motivates the construction of the underlying new-physics Lagrangian. Of course, Lagrangian consistency is a more stringent condition than OSET consistency, and feeds back into this analysis.