What is high energy physics? Go to a beach, pick up a grain of sand and ask yourself, "What is inside this insignificant piece of matter?" During the last 50 years, this age old question about the structure of matter has led physicists through a series of discoveries of "elementary" particles of ever decreasing size. A combination of experimental measurements and theoretical understanding of structure at various length scales has revealed fundamental symmetries about particle "types" and about the forces that govern their interactions. The search for further symmetry has guided us to predict "sub-structure" at even smaller length scales. Current theories like spontaneous symmetry breaking, supersymmetry and technicolor provide a rich spectrum of new particles that the experimenters in high energy physics hope to discover and continue on our path towards understanding the nature of fundamental forces.

How do you do it? The task of probing very small length scales requires collidingparticles with very highenergies. Professor Tripathi's projects at particle accelerator facilities have included the H1 Experiment at the DESY Lab in Hamburg, Germany and the Dě Experiment at Fermilab in Batavia, Illinois. For the past decade, we have been gearing up to work on the CMS Experiment at the Large Hadron Collider at CERN in Geneva, Switzerland. In order to measure particles at these state-of-the-art machines, we need to construct highly complex detectors. The effort at UCD is focused on muon detection for which we have produced several important components. Find out more details about UCD involvement in the CMS experiment.

How else can you do it? One can also look for signatures of massive particles that were produced within the high energy densities that existed in the early universe. Some of these particles could still be around. One such remnant could be the neutralino, which is the lightest supersymmetric particle (and hence, stable) and a candidate for dark matter in the universe. Annihilations of neutralinos will produce high energy gamma rays. Professor Tripathi is operating the Solar Two ACT to search for a neutralino remnant and also to look for clues that will help solve some mysteries in the gamma-ray spectrum of active galactic nuclei.

What is needed in order to do it? Constructing complex detectors for high energy physics experiments requires development of detection techniques. Professor Tripathi's efforts in detector development have mostly been in the area of silicon detectors and front-end electronics. One such device is a silicon pixel detector that has minute detection elements (about 100 microns in each dimension) and is able to measure a large flux of particles (about 10^6 particles/cm^2/s). In order to design and fabricate this device, we have had to acquire and/or develop various techniques, for example, custom integrated circuit design, indium bump-bonding, silicon wafer-bonding, single photon counting detectors and characterization of custom chips. Find out more about Electronics Development and Linear Collider R&D work at UCD.

How can you get a job after doing it? Most of Professor Tripathi's students have continued in academics by moving on to postdoctral positions at other universities, while others have moved into industrial R&D positions. Some of the technical work is done in collaboration with the electrical engineering department and national laboratories. This interplay between physics and engineering provides graduate students with a rich atmosphere for developing their own ideas and choosing for themselves a variety of career directions to pursue.

E-mail mani@physics.ucdavis.edu

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