Brown physicists and collaborators open a new window on nature

A recent announcement from the DZero Collaboration at Fermi National Accelerator Laboratory has created a major stir in the particle physics community, which includes a number of Brown physicists.

On December 8, the lab announced the first evidence that top quarks are produced not only in top-antitop quark pairs through the strong interaction but also as single top quarks and antiquarks through the electroweak interaction.

The announcement is particularly exciting for Associate Professor of Physics Meenakshi Narain, who played a key role in the analysis of data that led to the discovery of this particle 11 years ago.

For this most recent finding, Narain and Leonard Christofek, a postdoctoral research associate in physics, worked with Boston University postdoctoral researcher Shabnam Jabeen and graduate student Monica Pangilinan.

DZero is a major international collaboration that studies proton-antiproton collisions at Fermilab's Tevatron collider, the world's fastest energy accelerator. Brown physicists were founding members of DZero; Professor David Cutts, Associate Professor Greg Landsberg, and Professor Richard Partridge continue to have major roles, with responsibilities for key components of the detector such as data acquisition and luminosity monitor. They also have held leadership positions in the physics analysis of the data collected. With Narain, they shared the excitement of the top quark discovery in 1995. At the time, Partridge also lead an analysis group with a direct role in this discovery.

The heaviest known elementary particle, the top quark has the same mass as a gold atom and is one of the fundamental building blocks of nature. In this case the top quarks were produced in high-energy collisions of protons and antiprotons at Fermilab's Tevatron particle accelerator.

Discovering and measuring this new production process for the top quark is important. The analysis may reveal unexpected properties of the heaviest quark. Measuring how often top quarks are produced in this way can also tell physicists whether even more massive and so far undetected quarks exist. Study of single top decays can also help in the search for another particle that theorists have predicted to exist - the Higgs Boson, believed to be responsible for generating the mass we associate with elementary particles.

Physicists had been looking for the single top quark production process for many years. The signature of single top quark production is hard to distinguish from many other processes that occur in proton-antiproton collisions. Only with new analysis techniques, used to study the large amounts of new data collected at the Tevatron, were physicists in DZero finally able to detect this process.