Prof. Christoph M E Paus

Professor Paus' research focuses on the understanding of elementary particle physics from the experimental point of view. For the past 30 years, the Standard Model of particle physics has been successful in describing a huge variety of experiments performed in this field.

During his time at the L3 Experiment -- one of the four LEP experiments at the international particle physics research center CERN -- Paus was deeply involved in the most precise and complete tests of the Standard Model done to date. Although the measurement of electroweak quantities from decays of the Z boson did not reveal any problems in the model, its parameters were determined to a high precision. The measurements, in fact, reached a precision of several tens of PPMs and confirmed several levels of quantum corrections of the Standard Model.

Professor Paus' new project within the CDF experiment at the elementary particle research center, Fermilab, is to probe another not very well measured nor understood aspect of the Standard Model. The structure of matter generally follows certain symmetries but the Standard Model predicts small amounts of violation of those symmetries. With the CDF experiment, Prof. Paus is presently preparing important measurements for understanding the phenomena of CP symmetry violation. The violation of this symmetry is essential for the presently observed asymmetry of matter and antimatter in our visible universe.

Research is in experimental high energy particle physics -- Professor Paus carries out his research at Fermilab, which is located in Batavia, Illinois, about 35 miles west of Chicago. Paus is a member of the CDF, collaboration, which consists of approximately 500 physicists. Together we have constructed a large experimental apparatus - the CDF detector - that records data from proton-antiproton collisions. The collisions are produced by the Tevatron, the highest energy particle collider in the world, at center-of-mass energies of 2 TeV. Using the data from our detector, we study a wide variety of phenomena in particle physics. The most important result achieved was the discovery of the top- or t-quark, the last unobserved fundamental fermion in the Standard Model of particle physics. This discovery was announced in April, 1995.

Research focuses on the physics of particles called hadrons that contain bottom- or b-quarks. The b-quark is the weak isospin partner of the top-quark and thus of particular interest. By studying the decays of these B-hadrons, we deepen our understanding of the electroweak interaction. In particular, the decays of these particles are expected to violate the combined symmetry operation of charge conjugation and parity or CP. CP-violation is of great interest, because it must exist to explain the observed predominance of matter over anti-matter in our Universe.

So far CP-violation has only been observed as a few parts per thousand effect in the decays of neutral K-mesons. In contrast, B-mesons are expected to exhibit CP-violation at a level as high as 0.5. Currently I am developing together with a group of people the experimental techniques that will lead to the observation of CP-violation in the decays of B-mesons if our current theoretical understanding of this effect is correct.