Applications of QCD in the Standard Model and Beyond

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This grant proposal involves work aimed at elucidating the dynamics of the Standard Model of particle physics, both in the context of the Standard Model itself, and in the context of determinations of Standard Model contributions to processes currently under investigation as part of the intensive, ongoing experimental search for physics beyond the Standard Model either underway at present, or about to start, at major experimental facilities throughout the world. In these processes, a precision understanding of Standard Model contributions is crucial to the success of the very expensive experimental programs since these contributions serve as backgrounds which must be thoroughly and precisely understood if beyond-the-Standard-Model effects are to be identified. Of particular importance in this regard is the determination of the effects of the strong interactions, which, because of their strength (1) can be very numerically significant and (2) are amenable to treatment using a much more limited set of theoretical techniques than are effects produced by the weaker electromagnetic and weak interactions. Strong interaction effects will be evaluated using Quantum Chromodynamics (QCD), the theory of the strong (nuclear and sub-nuclear) interactions, employing a number of rigorous, well-established theoretical techniques, including large scale numerical simulations (lattice QCD). We will use these techniques, in combination with experimental data from various collider facilities, to make state-of-the-art determinations of Standard Model parameters such as the strength of the strong interaction coupling and the up-strange Cabibbo-Kobayashi-Maskawa matrix element, a parameter which describes how rapidly a hadronic state containing a strange quark can decay into states in which the strange quark has been converted into an up quark. A new determination of this latter quantity based on the strange hadronic decays of the heavy tau lepton is of particular interest in view of current indications of the possibility that the weak interactions couple with different strengths to the different leptons, a possibility that would provide unambiguous evidence for the presence of physics beyond the Standard Model. We will also continue previous work on looking for novel ("exotic") states of hadronic matter. Part of the work involved in this proposal will also involve creating a suite of computer programs which will allow experimentalists at the new major Belle II facility in Japan to perform theoretical, QCD-based analyses of experimental data on hadronic decays of the tau lepton that will be generated as part of the multi-year program at the Belle II facility, expected to begin physics runs in 2018. The work in this grant proposal will thus also serve to increase the effectiveness of the collaboration between particle theorists and experimentalists.