Early ATLAS B-physics with the first 10 – 100 pb-1

Early data of ATLAS will allow several B-physics measurements. Already with few pb-1 the ratio of the cross section of prompt J/ψ to indirect J/ψ cross-section will be measured with statistical precision of <5%. With 10 pb−1, the cross section of heavy quarkonia like J/Ψ and Y will be measured in a pT range from 10-50 GeV/c. The J/y and Y polarization is expected to be measured with a precision of 0.02 to 0.06 and 0.2 for Y, respectively. Another measurement with first data will be the estimation of the cross section of the exclusive decay B+ →J/yK+, which will be used as a reference channel for e.g. rare B-decay searches as well as for detector performance studies. The measurement of the invariant masses of the B-mesons and lifetimes using these decays will allow detector performance checks.