• Origin of mass and flavor
• Search for new symmetries of nature
• Neutrino physics
• CP violation
• Heavy quarks
• Extra dimensions
• Effective field theory
• Strong interaction field theory
Broadly stated, the aim of the experimental particle physics group at the University of Pittsburgh is to understand the fundamental constituents of matter by searching for new subatomic particles and by measuring precisely the properties of the known particles and interactions.
The group’s longest-running effort has been with the CDF experiment at Fermilab’s Tevatron, which collides protons and antiprotons at what has been the highest energy available in the world. At the Tevatron, the University of Pittsburgh group (Joseph Boudreau and Paul Shepard) has played a leading role in the commissioning and operation of the CDF silicon microvertex detectors and in the development of core software. The group has been involved in the studies of heavy quark physics and in the investigations of CP violation and its role during baryogenesis in creating the current asymmetry between matter and antimatter.
In 2009, the energy frontier moved to the Large Hadron Collider (LHC), located at the CERN laboratory in Switzerland, which has seven times the energy of the Tevatron. The detectors surrounding LHC’s four interaction regions, where the two intense proton beams collide, are instrumented with millions of sensors to record traces of the particles emerging from the collisions. Some of them may be the decay products of ephemeral heavy particles such as the long-sought Higgs boson, which is related to the origin of mass. The University of Pittsburgh group (Boudreau, Bill Cleland [emeritus], James Mueller, Vladimir Savinov, and Vittorio Paolone) is involved in the ATLAS experiment at LHC. The group has built the interface between ATLAS calorimeters and the Level-1 trigger, and it is responsible for maintaining that branch of the electronics. The group also plays a leading role in the development of object-oriented detector simulation software for the experiment.
The data that will be collected at the LHC are expected to help answer important questions about fundamental forces and the evolution of the universe right after the Big Bang. The University of Pittsburgh ATLAS group is involved in the studies of heavy quark physics and the search for supersymmetric particles and leptoquarks, hypothetical particles predicted by new physics models. The discovery of leptoquarks would help to elucidate the full symmetry group of nature and the mechanisms responsible for its breakdown; it also would indicate that the energy scale at which these mechanisms turn on is within the reach of the LHC. Supersymmetric models could provide an explanation for the dark matter that binds together the galaxies in the universe. Such models also predict the existence of several varieties of Higgs bosons and hypothetical intermediate vector bosons. The group also is involved in the search for heavy Majorana neutrinos and any new intermediate vector bosons. Should new heavy neutrinos be discovered at LHC, they could be used to explain the masses of the three known neutrinos via the seesaw mechanism. Possible CP violation in the decays of these heavy neutrinos could help to explain baryogenesis. In addition, the group is involved in the analysis of generic final states with electrons and muons of high momenta. The detection of such particles in the data could indicate the existence of more than three spatial dimensions, and could signal the unification between gravity and the rest of the fundamental forces at a much lower energy scale than is normally expected. If such discoveries are made, short-lived microscopic black holes could be detected and studied at LHC.
Similar issues also are addressed from another perspective by studying neutrinos. At the same time, fundamental properties of neutrinos such as mass and mixing angles are still poorly understood. The discovery of neutrino oscillations/masses in 1998 and the close connection between neutrino issues and cosmology have made neutrino physics a vibrant field of research. The neutrino group at the University of Pittsburgh (Steven Dytman, Donna Naples, and Vittorio Paolone) has a long history of involvement in neutrino experiments, including DONUT (experimental confirmation of the tau neutrino), NuTeV (extensive new information about structure functions, a precise measurement of the Weinberg angle, and searches for exotic particles), and MINOS (improved limits on oscillations and searches for exotic effects such as CPT violation).
Present efforts of the group include the MINOS, MINERvA, and T2K experiments. They are the first of a new generation of more sensitive experiments. The group is responsible for the anti-neutrino mixing analysis in MINOS. MINERvA (Fermilab) will measure low-energy neutrino interactions as a way to significantly improve the accuracy of neutrino oscillation experiments and to study the strong dynamics of the nucleon and nucleus that affect the interactions. The next important step in understanding neutrino properties is the T2K (Tokai to Kamioka) experiment in Japan, which is designed to compare and study the properties of an accelerator-generated beam of neutrinos sampled at the Tokai “near detector” (280 m downstream from where the neutrinos are produced) and the Super Kamiokande “far detector” (295 km from the near detector). The experiment will make precision measurements of the oscillation of one type of neutrino into another to measure better the mass differences and mixing parameters. The group is responsible for the readout electronics and part of the calibration effort of both of the new experiments.
The descriptions of these research programs make clear that, in the years ahead, graduate students who join any of the experimental particle physics groups will be working with large, international teams of scientists on collecting and analyzing data. Upon completion of course-related requirements, graduate students will typically take up residence at the laboratory where the experiment is being conducted.
Six faculty members (Daniel Boyanovsky [also astrophysics and cosmology and condensed matter physics], H. Anthony Duncan, Ayres Freitas, Adam Leibovich, Ralph Roskies, and Eric Swanson) conduct research in theoretical particle physics, covering a range of topics centered on exploring the properties of, and the physics beyond, the Standard Model. The studies of the Standard Model deal largely with the emergent properties of strongly interacting quantum field theory, top quark physics, and electroweak precision constraints.
The research on models beyond the Standard Model focuses on analyzing collider signatures expected from LHC, determining constraints from current experimental data, and searching for dark matter candidates. Furthermore, the cosmology of the early universe is studied, with emphasis on inflation and phase transitions. A variety of tools are employed in this research, including novel perturbative and nonperturbative methods of quantum field theory and statistical mechanics, model building, lattice field theory, and effective field theory. The theoretical particle physics group is working in collaboration with many national and international partners, thereby creating a vibrant working environment for graduate students.