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Unformatted text preview: Lecture 1, January 29 2004 1 A theorist’s view of collider phenomenology The principal questions are: For any given model of new physics, • What are the discovery signatures? • What is the discovery reach of collider X? • How do we distinguish this model from the rest? In order to answer these questions, we follow the recipe. 2 Recipe 2.1 Define the theory In order to define the theoretical framework, we need to specify: • The new particles and their quantum numbers (spin, charge, color, etc.) • Their interactions at the relevant energy scale , i.e. the Lagrangian describing the new physics, with parameters given at the collider energy scale. Often the new physics input parameters are given at higher energies, e.g. the GUT scale or the Planck scale, in which case we need to RGE evolve them down to the electroweak scale. But sometimes we need to RGE evolve up , as in the case of the fermion Yukawa couplings. The set of new physics input parameters forms the “parameter space” of the new physics model. • We also need to identify potentially interesting regions of the parameter space. For example, certain regions may already be ruled out from direct searches, from indirect constraints (precision electroweak data, flavor-changing neutral current processes) or simply because of theory bias, e.g. they do not have a good dark matter candidate or are fine-tuned. • Given the Lagrangian, we can derive the Feynman rules for the new physics model and do some preliminary computations of relevant particle properties, for example the mass spectrum of the new particles (at tree-level or one-loop, as appropriate) and their widths (lifetimes). 2.2 Production cross-sections of new particles Next we have to compute the production cross-sections of the new particles, as they determine the expected total number of events in which new particles are present: N total = σ S L, (1) 1 where σ S is the cross-section for a particular final state, and L is the total integrated lumi- nosity of the data collected in the collider experiment. For example, during the Tevatron Run I each experiment collected about 110 pb- 1 , while in Run II there is hope for something like 8 fb- 1 . In the initial stages of the LHC the data taking rate will be 10 fb- 1 per year....
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- Spring '12
- Particle Physics, NS, Higgs boson, new particles, new physics