J/Psi Physics at ATLAS

These slides are prepared for a 30' talk on "JPsi physics at ATLAS" at the International Workshop IHEP-LHC-2010 (Protvino, 19-21Oct). The content summarizes the ATLAS results in ATLAS-CONF-2010-062, ATLAS-CONF-2010-078 and ATL-COM-PHYS-2010-518. The abstract submitted to the workshop follows. J/Psi and quarkonia physics is at reach already with the early LHC data. The ATLAS results on J/Psi->mumu double differential inclusive production cross section and on non-prompt to prompt J/Psi production ratio are discussed in this contribution. These preliminary measurements are based on a limited integrated luminosity sample of data collected in the initial phase of 2010 LHC running at 7 TeV. They, however, demonstrate the potential of ATLAS to perform quarkonia precision measurements in the future that can hopefully shed light on the still unclear aspects of quarkonia physics. In addition, the high cross section of the narrow J/Psi resonance allows for a data driven determination of the ATLAS detector performance for lepton reconstruction in the low transverse momentum regime. A few examples of performance studies based on J/Psi are summarized in this report.