Production Cross-Section Measurements and Study of the Properties of the Exclusive $B^{+} \to J/\psi K^+$ Channel

In the initial phase of the LHC operation at low luminosity several Standard Model physics analyses will be performed in order to validate the ATLAS detector and trigger system. The $B^{+} \to J/\psi K^+$ channel can be observed with the first ATLAS data at LHC and can be used for detector performance studies. This channel will provide a reference in the search for rare $B$ decays. It will also be used to estimate the systematic uncertainties and efficiencies of flavor tagging algorithms, needed for $CP$ violation measurements. The prospects to measure the $B^{+}$ mass, its total and differential production cross sections and lifetime with the first ATLAS data, are described in this note.