D0 announces discovery of new top quark production process
March 09, 2009
The D0 Collaboration at Fermilab has submitted a paper to Physical Review Letters announcing the discovery of a new production process for the top quark. BU Associate Professor Ulrich Heintz, who co-led the top quark physics analysis group of the D0 Collaboration between 2006 and 2008 and postdoc Shabnam Jabeen have contributed directly to the work that resulted in this discovery.
The top quark is the most massive elementary particle known. It was discovered at Fermilab in 1995 by the D0 and CDF experiments. The Tevatron collides protons and antiprotons at an energy of 2 TeV, the highest energy particle collisions ever produced in the laboratory. In some of these collisions top quarks are created, most of the time together with their antiparticle, the anti-top quark, through the strong force, the force that holds together the atomic nucleus. Theorists have predicted that sometimes only a top quark or only an antitop quark is created through the weak force, which is responsible for nuclear decay. Scientists at Fermilab have been searching for this so-called single top production mechanism for many years. The D0 Collaboration reached a major milestone in December 2006, when it announced that it had observed evidence for this process, indicating that it had observed some collisions in which top quarks seemed to be produced singly but not quite enough to be certain (see BU faculty and students integral to Fermilab discovery). In the meantime the D0 Experiment has collected more than twice as many data and many more such collisions were found confirming the 2006 result and establishing single production of top quarks beyond any reasonable doubt.
This discovery is significant because the interaction of the top quark through the weak interaction can only be measured in this process and its measurement may be sensitive to possible new fundamental interactions or elementary particles that have not yet been directly observed. The observation of this process thus creates a whole new laboratory in which the standard model can be tested. The measurement by the D0 Experiment shows that single top quark production occurs at a rate consistent with the prediction of the standard model of particle physics, the theoretical framework that summarizes our understanding of the fundamental particles and their interactions.