The first photograph of the sun taken by "neutrino light". Exposure 503.8 days and nights by Super-Kamiokande

Table of Contents Introduction Experimental Particle Astrophysics Super-Kamiokande GLAST JACEE The ALEPH Detector at CERN The ATLAS Experiment at LHC (CERN) The DØ Experiment at the Tevatron Run II (Fermilab) Faculty UW Physics Department Home Page

Research pursued by this group seeks an understanding of the structure of matter and the forces that govern its behavior. Our experiments are carried out at particle accelerators and astrophysical observatories around the world. Using detectors and advanced data-acquisition equipment, much of it designed and built in our laboratories on campus, faculty members and graduate students make measurements that address these fundamental aspects of our natural world. Most of what is currently known about elementary particles is described by the "Standard Model" of particle physics. Recent work in this field has concentrated on testing the Standard Model in efforts to find the extent to which it can be extended to cover phenomena involving higher energies, or shorter distances. Although it is known that the theory must fail at sufficiently short distances, to date it has proven with few exceptions to be remarkably robust. We have entered an era in which more sensitive astrophysical experiments and new, higher energy accelerators will provide the means to make critical tests that will illuminate aspects of particle behavior that are not explained by the Standard Model. We have already made a definitive measurement of the existence of non-zero neutrino mass which breaks some Standard Model symmetries.

Outstanding issues in the Standard Model include the origin of mass and the mechanism of "symmetry-breaking". The Standard Model posits three distinct families of quarks and leptons, all of which have now been discovered. However, it contains no clue as to why the heaviest quark has a mass many thousands of times heavier than the lightest quark. The model also postulates the well established high energy amalgamation of the weak nuclear force (responsible for the decay of radioactive particles) and electromagnetism into a simple force called the "electroweak" force. However, it has no explanation of why or how the underlying symmetry between these two forces is broken to produce the very different phenomena (radioactivity on the one hand, and electromagnetism on the other) that we observe at low (normal) energies. Intriguing arguments involving larger symmetry groups for quarks and leptons have been made with the prediction that the nucleons must be unstable with very long lifetimes. Our group is participating in the efforts to find answers to these intriguing questions.

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Experimental Particle Astrophysics

Faculty: Wilkes

The Experimental Particle Astrophysics group mainly uses natural cosmic radiation as a source of elementary particles to study the character of the fundamental interactions, and the structure and evolution of large-scale astrophysical systems. Current projects include the world's largest neutrino detector, a long base line neutrino experiment with a neutrino source from the KEK proton accelerator (the K2K experiment), a satellite born gamma ray observatory, and the use of balloon-borne detectors to extend direct observations of the primary cosmic ray spectrum to the highest accessible energy range.

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Faculty: Wilkes

Super-K, the world's largest and most sensitive underground neutrino and muon experiment, has been taking data since April, 1996. At the Neutrino 98 International Conference, Super-Kamiokande announced the exacting evidence for the existence of neutrino oscillations. The implications are that neutrinos have non-zero mass and is the first solid evidence for physics beyond the Standard Model.

The experiment is very large imaging Cherenkov detector comprised of a stainless-steel tank, 40 meters across and 40 meters tall, containing 50,000 tons of ultra-purified water and instrumented with 14,000 photomultiplier tubes, located 1000 meters underground near Kamioka, Japan.

The mission of Super-K is to measure the neutrino flux as a function of energy and direction with unprecedented precision and statistical accuracy with the goal of measuring the flavour oscillation of neutrinos without the necessity of verifying any particular model of neutrino flux generation. The neutrino sources that have been examined are the solar neutrinos produced by fusion in the sun and the neutrinos produced by cosmic rays in the earth's atmosphere. The other goals of this experiment are to search for nucleon decay (post-standard model physics) and to measure the physics at the core of a supernovae during the important first few seconds.

Our group plays an active role in operating and maintaining the detector and in the most interesting physics analysis efforts. Having established the existence of neutrino oscillations we are embarked on a new project to make a precision determination of the oscillation parameters for the neutrinos. In 1999, we will produce neutrinos at a beam at KEK (National Accelerator laboratory in Japan) and direct it towards the Super-K experiment. The precise measurement of the proper time from neutrino birth to detection will permit us to make a precise determination of the neutrino flavour oscillation parameters.

A view of the interior of Super-K during its fill with ultra pure water

An artists view of the Super-K experiment.

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Faculty: Burnett

The Gamma-ray Large Area Space Telescope (GLAST) will begin a new epoch of space-based physics investigation. By measuring celestial gamma rays in the 10 MeV to 300 GeV portion of the electromagnetic spectrum, GLAST can use the most powerful particle accelerators in the universe as cosmic laboratories to explore the link between gravitational and quantum physics in the extreme environments of supermassive black holes, neutron stars, and gamma-ray bursts. On cosmological scales, GLAST can explore the era of star formation, the physics of dark matter, and the creation and evolution of galaxies.

Our group is involved in software development for this instrument, which is scheduled for launch in 2005. Software plays two important roles: simulation of the physics of particles traversing the instrument, and the electronic responses, allows an understanding of the capabilities and optimization of the design. On board software is also a crucial to the functioning of the instrument.

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Faculty: Wilkes

The Japanese-American Cooperative Emulsion Experiment (JACEE) is an ongoing US-Japan collaboration studying the fluxes and interactions of ultra-high energy primary cosmic ray protons and nuclei.The detailed structure of cosmic ray spectra as a function of energy and atomic number provides information on their production and acceleration, and thus on particle interactions at energies far higher than attainable with particle accelerators.

Most ultra-high energy cosmic ray detectors are ground based and have to infer spectra from observations of particle cascades induced in the atmosphere by cosmic ray interactions at high altitudes. JACEE uses balloon borne detectors and has been very successful in extending the energy range of directly-measured cosmic ray fluxes.For the nuclear composition of primary cosmic rays up toward the knee in the spectrum around 1015 eV, the JACEE measurements are the world standard reference.In recent years, we have carried out a series of long-duration balloon flights in Antarctica, with more flights planned. Space Station experiments aboard the Japanese Experimental Module are also likely extensions of the JACEE program

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Faculty: Rothberg, Wasserbaech, Williams

Members of our group have made significant contributions to the design and construction of the ALEPH detector operating at the Large Electron Positron (LEP) collider at CERN and continue to lead important efforts to analyze data collected over the past decade. Some 5 million hadronic events recorded at the mass of the intermediate vector boson Z0 have provided a large range of tests for the Standard Model of particle physics. A new program at LEP2, an upgrade of LEP, will employ energies above the W+W threshold and continue into the 21st century. Searches for the Higgs particle and for super-symmetric particles, and details of the electroweak coupling will be the main focal points at LEP2. Members of our group have a particular interest in the nature and interactions of the tau lepton (the heavy analog of the electron and muon in the third lepton family). We expect to increase our participation during the coming years.

The Aleph Detector

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Faculty: Burnett, Lubatti, Rothberg, Zhao

The Large Hadron Collider (LHC), under construction at CERN, is expected to begin data-taking in 2005. Atlas is one of two very large detectors being built to operate at LHC. Physicists from around the world are collaborating in the design and construction of the detector. Our group is leading the US effort to design and construct a high precision muon detector that surrounds the region where counter-rotating, very high energy (7 TeV) protons will collide. Starting in early 1998 we will be building and testing the high precision muon detector proportional tubes and will be setting up a prototype electronic control system for the muon detectors. Many challenging hardware and software design problems are currently being solved in our laboratories by our faculty and students. Between now and the turn-on of LHC there will be numerous beam tests of detector elements and Monte Carlo modeling of the physics we will explore with the new accelerator. This experiment opens a new energy frontier that will provide opportunities to search for answers to the outstanding questions of particle physics: the origin of mass, and the mechanism of symmetry breaking.

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Faculty: Burnett, Lubatti, Zhao, Watts

The Tevatron RunII has been successfully taking data since 2001, after a complete upgrade of the Run I detectors that discovered the top quark in 1995. The DØ detector has been performing extremely well since then with added tracking capabilities and a new data acquisition system which is in part responsibility of the University of Washington group. The group is also participating in the construction of an innermost layer support for the silicon detector to be installed in 2005. We are actively involved in the analysis of top quark physics and have ample experience on searches for supersymmetric Higgs bosons. We currently have more than three times the data collected during Run I at a greater energy of 2 TeV and expect to increase this to at least forty times by the time the LHC comes online. This unprecedented data sample will allow to do precision electroweak physics and search for physics beyond the standard model while preparing the way for the type of physics to be seen at the LHC. Graduate students collaborate on the day-to-day data tacking activities and data analysis on site, near Chicago, in an active and international environment such as Fermilab.

The DØ Collaboration

Dijet event in DØ

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Professor Thompson Burnett, Ph.D., University of California (San Diego), 1968
Professor Henry J. Lubatti, Ph.D., University of California (Berkeley), 1966
Emeritus Research Professor Paul M. Mockett, Ph.D., Massachusetts Institute of Technology, 1965
Professor Joseph Rothberg, Columbia University, 1963
Associate Professor Gordon T. Watts, Ph.D., University of Rochester, 1994
Professor (WOT) Jeffrey Wilkes, Ph.D., University of Wisconsin, 1974
Research Associate Professor Tianchi Zhao, Ph.D., Columbia University, 1987

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UW Department of Physics