Wisconsin is a member of the BaBar Collaboration at the PEP II accelerator at SLAC. The primary physics goal of the BaBar experiment is the discovery and systematic study of CP violation in decays of and mesons.

Our initial involvement in BaBar was focused primarily on development of the Silicon Vertex Tracker (SVT) with major contributions to both the hardware and software. Our hardware involvement included intensive testbeam activities at CERN as well as construction of the SVT in conjunction with the Pisa group. We developed major offline software for pattern recognition and reconstruction in the SVT, including algorithms which resulted in major improvements to charged particle tracking in BaBar. We are involved in the day-to-day running of the SVT to help maintain the high quality of the BaBar tracking.

Wisconsin's Research into CP Violation
Measurements of CP violation rely critically on the quality of B-flavor tagging. The Wisconsin group has been very successful in its effort to improve the overall tagging performance of BaBar. Exploiting the power of neural networks, we developed software which enabled us to significantly enhance the tagging power with respect to the BaBar algorithm detailed in the "BaBar Physics Book". We were heavily involved in analysis to determine the tagging performance directly from data. This work enabled publication of the first definitive measurements of CP violation in decays with BaBar data. The techniques we developed have been applied to the most precise measurement of the CP-violating asymmetry amplitude sin2beta to date (The BaBar Collaboration, "Measurement of the CP-Violating Asymmetry Amplitude sin2beta", Phys. Rev. Lett. 89 (2002) 201802).

With the establishment of sin2beta as a high-precision measurement, the Wisconsin group is currently engaged in the challenging task of extracting the CP-violating quantity sin2alpha (For preliminary results, see: The BaBar Collaboration, "Search for CP Violation in B0/anti-B0 Decays to pi+pi-pi0 and K+pi-pi0 in Regions Dominated by the rho+ Resonance"). This analysis is nearing the final stages of preparation for publication in Physical Review Letters. With the current luminosity, it is feasible to extract an effective measurement of sin2alpha in the near future. Our longer term goal is to develop a full Dalitz analysis involving the decays of both charged and neutral B mesons to rho - pi final states which will enable a measurement of the true underlying value of sin2alpha. The analysis to obtain the true value of sin2alpha has already begun and we are making major strides in three separate analyses to measure the branching ratios of the remaining rho - pi final states: rho+pi0, rho0pi+, and rho0pi0.

We anticipate publication of these analyses as part of our goal of achieving a full Dalitz analysis.

Wisconsin's Research into Rare Phenomena
The Wisconsin group is leading the search for the rare decay mode B+ -> tau+ nu. With the currently available data we expect to set the world's most stringent upper limit on the branching ratio. Observation of a significant signal with the present data would indicate the presence of new physics, such as Supersymmetry. In general, this decay process provides a clean probe of the Weak Nuclear Force. The presence of undetectable neutrinos in the decay brings difficult experimental challenges. The first results from this research on the current BaBar data set will be presented in March, 2003.

Wisconsin's Role in BaBar Operations
Our roles in the BaBar experiment have turned from SVT development to commissioning and daily operations; members of the group have been in charge of monitoring the real-time reconstruction of BaBar's 100 fb-1 of data, as well as commissioners for the SVT system and managers of the entire Data-Acquisition System (DAQ).