James T. Linnemann

Jim Linnemann
Professor
High Energy Experimental
linnemann At pa.msu.edu

Office: 3245 BPS
(517) 355-9200 extension 2125

Department of Physics and Astronomy
Michigan State University
3245 Biomedical Physical Sciences
East Lansing, MI 48824-2320

Teaching

Currently, I'm teaching Physics 191, an introduction to quantitative measurement for physics majors, engineers, and other scientists. I'm also teaching PHY 232, the second semester of a 2-term introduction to physics for science majors using algebra and trigenometry, rather than calculus. I particularly enjoy that we include material from 20th century physics, rather than stopping in the late 1800's as is too often the case in survey courses. We are now using Lon-CAPA to allow web-based individualized graded homework, as well as quizzes and exams

In the past, I've coordinated CBI Physics, which is part of project PHYSNET. CBI physics is a self-paced approach to learning physics which allows flexibility of scheduling and fosters student independence as learners. In addition, I am associated with project LITE, a major project in the college of natural science to develop a framework for production and presentation of online courses. I hope to use my background in computing, which is an important part of my research, to find links between these projects. I'll be working with Dr. Pete Signell, who pioneered CBI and has been blazing this particular trail for some time. It will be interesting to see similarities and differences of these projects with CAPA, another style of computer-intensive instruction which has linked with project LITE.

In recent years I've also taught Physics 252.This is the second introductory physics laboratory class. It starts with basic DC electrical circuits and moves on to AC circuits. The electrical experiments culminate in a lab where we wire everybody up and measure the electrical signals due to heartbeats! Then we turn to optical experiments, where we simulate the myopic eye with lenses, study ray optics, diffraction and interference with lasers. Finally, we use a prism spectrometer to measure the wavelengths of light emitted by atoms undergoing quantum changes of state (this is how quantum mechanics got its start), and then study the basis of color vision by observing white light spectra and how color filters absorb ranges of wavelengths to differently stimulate the eye's color receptors. Along the way, we learn how to estimate uncertainties and use them to test whether observations match theory.

Research

I'm an experimenter in High Energy Physics and Astroparticle Physics. My main effort has been in the D0 experiment, a collider experiment at the Fermilab Tevatron. I often work intensively with computers, particularly in the area of triggering. A hadron collider can produce as many as a million proton-antiproton collisions in a second. Since our apparatus records more than 1/4 Megabyte of information about each interaction, they can't be all recorded and analyzed in detail. "Triggering" the apparatus is deciding which of these interactions is interesting enough to keep. In our previous data run, recorded 2 events per second. The rejection of "less interesting" events takes place in 3 levels of triggering. The first level lasts a few microseconds (millionths of a second), and requires sophisticated custom hardware. Luckily, our electronics shop and its talented designers (Dan Edmunds and Philippe Laurens) specialize in just this sort of thing, and MSU built a large fraction of the trigger for D0. The second level of triggering is more relaxed in pace, allowing up to 100 microseconds per event. This usually is carried out in a mixture of specialized hardware and carefully written software on very fast processors. The third level takes place in more conventional computers, albeit in somewhat rigorous conditions with strict requirements on memory usage and speed. Here the time scale is 50-200 milliseconds per event for a decision.

In our previous data run, I was in charge of the physics algorithms for the third level trigger selecting events online: we had 200 milliseconds to decide which of the 2% of events to keep. Our programs ran in an array of 48 microcomputers, and processed more than a 10⁹ events. Looking for a further challenge, I've moved up to the second level trigger for the next run (2000-2003 or so), and expect to have a hand in examining nearly 10¹² events. Postdoc Roger Moore will be writing code (in C++, with a specially modified version of the Linux operating system) for special versions of PC processors to control data flow and carry out the triggering decisions. The level 2 trigger is the first opportunity to carefully match up information from different parts of the apparatus. This allows us to verify whether a set of signals is really consistent with, for example, the track of a high energy electron, which would be a good tipoff that this event is interesting and unusual. Real trigger decisions will involve several such conditions, in up to 128 different combinations.

In the course of this work, I've also developed interests in software engineering, the art of making reliable programs to do physics. I have also developed a fascination with statistics, the basis for many of the techniques we use both to tell signal from background events, and to analyze our data. Since the interactions we measure are directly governed by quantum mechanics, and since we often seek rare occurrences, we almost always use statistical techniques to measure rates, test theories, and set limits on occurrences of rare processes. Dennis Gilliland and Raoul LePage of the MSU statistics department are among the people I've worked with on these problems.

I've been involved with several different analyses of D0 data. I had the great pleasure and excitement of participating in the discovery of the top quark in 1995. Jim McKinley, the first Ph.D. thesis student I supervised, measured the Drell-Yan process, a rare QCD process producing pairs of electrons from proton-antiproton collisions (MSU theorist C.P. Yuan, a member of the CTEQ phenomenology collaboration, is one of the world experts in the theory of this process) . My second student, Rich Genik, did a thesis on a search for supersymmetric (SUSY) particles, in particular, squarks and gluinos decaying into electrons or muons. You can look at some of the relevant theory papers here. We applied a systematic framework for interpreting the results to set limits on the possible parameters to supersymmetric models, which would extend and unify the standard model of particle physics. Maybe next run (we started in March 2001), we'll find SUSY instead of setting limits; that's what my current graduate student, Adam Yurkewicz, hopes. In the meantime, you can see some of the physics highlights from the last physics run.

In 2003, I spent a 7-month sabbatical leave in New Mexico. As a result, I joined the Milagro experiment, which searches for cosmic rays, high enegy particles from space which hit the earth constantly. The particular kind we'll be looking for come in the form of extremely high energy photons . TeV gamma rays is the techical jargon --particles of light packing more energy than one of the protons in the Fermilab TeVatron collider beams I usually work with. These photon cosmic rays are a rarer by a factor of a thousand than the usual cosmic rays of the same energy, most of which are protons, not photons. But the photons are interesting, because their direction isn't confused by magnetic fields in the galaxy, and they can point back to interesting astrophysical sources. And there's a good professional challenge in using statistical techniques to separate out these interesting signals. Recently, graduate student Aws Abdo joined me in this exciting project.

If we don't find supersymmetric particles at the Tevatron, I intend to continue the search at the next-generation collider in Europe with the Atlas experiment, scheduled to start in 2007 at the CERN accelerator complex in Geneva Switzerland, where I did my postdoctoral work.

CERN, by the way, is the particle physics lab where the World Wide Web was invented as a tool to help communication within international collaborations to do particle physics, such as D0 and Atlas. Now that's what I call a spinoff!

Life outside of physics

The best part is spending time with my wife and my daughter. My daughter is a curious nine year old who gives us the privilege of seeing the world through new eyes. She enjoys singing, drawing, making things of paper, dancing, and singing, and playing piano.  For me, music, especially jazz , is a great pleasure. Of the sites listed, I especially enjoy Michael Zwerin's and WNUR. I serve on the board of Happendance, a local professional modern dance troupe with an excellent company school.  Happendance not only performs for the public, but also has an active outreach program, performing and teaching motion in schools.

Updated August 20, 2002