University of Oregon

Past experiments and theoretical analysis have led to a precise description of the Nature's weak nuclear force, and the force of electromagnetism.  This precise description is called the standard model of electroweak physics. These two forces appear on an equal footing in many aspects within the electroweak model, but differ in a significant way: they are transmitted through space by "field" particles with very different masses.  The electromagnetic force is mediated by a massless "field" particle, the photon. On the other hand, the weak nuclear force, which is seen naturally as radioactive decay, for example, is mediated by very heavy particles, the W bosons, and the Z boson.

What brings about this important difference in the mass of these "field" particles? This mass difference leads to much of the difference in how the forces are experienced in Nature.  The difference is known technically as electroweak symmetry breaking. The Oregon group participates in the ATLAS experiment to investigate this question.

Four faculty, one research associate, and three graduate students are presently working on ATLAS.  Since Oregon joined ATLAS early in 2006, the group has devoted its effort to the process of selection of interesting events generated by the collisions of high energy particles within the ATLAS detector.

Many times more events are produced than can be recorded. A High Level Trigger provides an important step in this selection process.  Oregon's interest here has been particularly related to selecting tau leptons. Tau leptons are the heaviest leptons, and in many theoretical models are particularly connected to possible evidences of new physics.  Optimizing the trigger for their detection is therefore an important activity.  Oregon has been working to use the inner tracker data to do this.

As the ATLAS detector collects data from collisions, and data analysis becomes possible, the Oregon group plans to explore the general theme of electroweak symmetry breaking described above through a few different physics studies.  These include tau physics, heavy Z boson searches, and black hole production.