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for how particles will behave at smaller distances than physicists have experimentally studied so far. Measurements provide clues to help us distinguish among competing candidates. We don’t yet know what the new underlying theory is, but we can nonetheless characterize the possible deviations from the Standard Model. By thinking about candidate models for underlying reality and their consequences, we can predict what the LHC should reveal if the models turn out to be right. Our use of models admits the speculative nature of our ideas and recognizes the plethora of possibilities that might agree with existing data and explain as-yet-puzzling phenomena. Only some models will prove correct, but creating and understanding them is the best way to delineate the options and build up a reservoir of compelling ingredients.

Exploring models and their detailed consequences helps us establish what experimenters should search for—whatever might be out there. Models tell experimenters the interesting features that characterize new physical theories so that experimenters can test whether model builders have correctly identified the elements or the physical principles that guide the system’s relationships and interactions. Any model with new physical laws that apply at measurable energies should predict new particles and new relationships among them. Observing which particles emerge from collisions and the properties they have should help determine the type of particles that exist, their masses, and their interactions. Finding new particles or measuring different interactions will confirm or rule out models that have been proposed, and pave the way for better ones.

With enough data, experiments will determine which underlying model is the right one—at least at the level of precision, distance, and energy that we can study. The hope is that at the smallest distance scales that we can probe at LHC energies, the rules for the underlying theory will be simple enough to allow us to deduce and calculate the influence of the associated physical laws.

Physicists have lively discussions about which are the best models to study and what is the most useful way to account for them in experimental searches. I’ll frequently sit down with experimental colleagues and discuss with them how best to use models to guide their searches. Are benchmark points with specific parameters in particular models too specific? Is there a better way to cover all the possibilities?

LHC experiments are so challenging that without definite search targets, the results will be overwhelmed by Standard Model background. Experiments were designed and optimized with existing models in mind, but they are searching for more general possibilities as well. It is critical that experimenters are aware of a big range of models that span the possible new signatures that might emerge, since no one wants specific models to overly prejudice the searches.

Theorists and experimenters are working hard to make sure we don’t miss anything. We won’t know which, if any, of the different suggestions is correct until it is experimentally verified. Proposed models might be the correct description of reality, but even if they are not, they suggest interesting search strategies that tell us the distinguishing features of new as-yet-undiscovered matter. Hopes are the LHC will tell us the answers—no matter what they turn out to be—and we want to be prepared.

CHAPTER SIXTEEN

THE HIGGS BOSON

On the morning of March 30, 2010, I awoke to a flurry of e-mails about the successful 7 TeV collisions that had taken place at CERN the night before. This triumph launched the beginning of the true physics program at the LHC. The acceleration and collisions that had taken place toward the close of the previous year had been critical technical milestones. Those events were important for LHC experimenters who could finally calibrate and better understand their detectors using data from genuine LHC collisions, and not just cosmic rays that had happened to pass through their apparatus. But for the next year