Global QCD Analysis and Precision Electroweak Physics in High Energy Collider Phenomenology

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This award funds the research activities of Professors Jon Pumplin, Daniel Stump and C.-P. Yuan at the Michigan State University (MSU).Support for this project will contribute to understanding the fundamental nature of the physical universe--the particles that comprise it and their interactions--as revealed by experiments in high energy physics. Current understanding of high energy physics is embodied in the Standard Model (SM). Protons and neutrons, and all other strongly interacting particles, are composed of fundamental particles called partons (quarks and gluons). Interactions between the partons are described by the theory of Quantum Chromodynamics (QCD). The proposed research involves the interplay between QCD theory and experimental data from many experiments, including recent experiments at the CERN Large Hadron Collider (LHC). This global analysis of data is necessary to deepen the understanding of QCD, and to determine the probability distributions of the partons in the proton. By understanding these distributions, it is possible to take interactions of protons with protons (which is what happens at the LHC) and determine the underlying quark-quark, quark-gluon and gluon-gluon interactions. This is essential for determining the underlying physics of the process, and was necessary for extracting, for example, the Higgs boson signal. These probability distributions are called "CTEQ Parton Distribution Functions", where CTEQ means "Coordinated Theoretical-Experiment Project of QCD". The project trains graduate students and postdoctoral fellows in theoretical high energy physics at MSU and at CTEQ summer schools. It also provides opportunities for undergraduate students to participate in forefront research through the REU program, and for high school teachers and middle school students to experience physics through summer programs sponsored by MSU and the State of Michigan.As noted, the resulting CTEQ Parton Distribution Functions have been essential to the interpretation of experiments at the world's leading high energy collider facilities: Fermilab (Batavia, IL), RHIC (Brookhaven, NY), DESY (Hamburg, Germany), and CERN (Geneva, Switzerland). Although the colliders at Fermilab and DESY have been turned off, data from those facilities are still important; in particular, final data from HERA run II are still to be incorporated in the present analysis when they become available. The proposed research will continue the PIs' world-leading contributions to lepton-hadron and hadron-hadron collider phenomenology. Complementary to the research on QCD, the group will also study the Electroweak (EW) sector of the SM, which is extremely successful in explaining and predicting experimental data spanning a range in energy from the atomic scale to the Z boson and top quark masses. Measurements of W, Z, top quark pair, single top quark and Higgs boson productions at the LHC, including both inclusive rates and relevant kinematical distributions, will provide major new input to the understanding of parton distributions during the next few years. At the same time, refinements of the parton distributions are necessary for progress in the EW sector, both for testing the SM in greater precision and for probing New Physics effects in high energy colliders.