Melvyn J. Shochet
Kersten Distinguished Service Professor of Physics
My research involves interactions between elementary particles at the highest manmade energies. For many years, this has been carried out with the Collider Detector at Fermilab (CDF), a massive detector that we built to study collisions between 1000 GeV protons and 1000 GeV antiprotons. With the large accumulated data sample, we have studied the strong and electroweak interactions and searched for new phenomena. Our most important result is the discovery of the top quark and the determination of its mass. Our latest top-quark mass measurement, which employs a new technique for significantly reducing the major systematic uncertainty, is (171.9 ± 2.0) GeV, by far the most precise measurement of the mass of any quark. From this value, one can calculate the top quark’s Yukawa coupling constant, the strength of its interaction with the Higgs Boson, the source of an elementary particle’s mass. The Yukawa coupling constant for the top quark is 0.99 ± 0.01, consistent with 1. This coupling to the source of mass is strong, unlike that of any other elementary particle, making it plausible that the top quark plays a special role in physics.
My group is now working on the ATLAS experiment at the CERN Large Hadron Collider (LHC), which will produce collisions 7 times more energetic than those at Fermilab. We will be analyzing the early data from the experiment, initially to understand the performance of the detector and then to search for new physical phenomena. We are also developing an upgrade to the trigger, which selects interesting collisions in real time for later study. Hadron collider experiments can efficiently and quickly select events that contain electrons, muons, or generic hadron jets. However it is much more difficult to identify heavy elementary particles, the bottom quark and tau lepton, because of very large backgrounds. The new phenomena that should appear at the LHC will likely be characterized by the creation of heavy particles. This makes triggering on bottom quarks and tau leptons a priority. We are designing a set of trigger electronics boards that can identify these objects more than an order of magnitude faster than can otherwise be done. This device is based on the very successful Silicon Vertex Trigger (SVT) that we and our Italian colleagues built for CDF.