Abstract
With an integrated luminosity of 2.47__fb(-1) recorded by the ATLAS experiment at the LHC, the exclusive decays B(s)(0)_J/__ and B(d)(0)_J/_K(*0) of B mesons produced in pp collisions at ís=7__TeV are used to determine the ratio of fragmentation fractions f(s)/f(d). From the observed B(s)(0)_J/__ and B(d)(0)_J/_K(*0) yields, the quantity (f(s)/f(d))[B(B(s)(0)_J/__)/B(B(d)(0)_J/_K(*0))] is measured to be 0.199±0.004(stat)±0.008(syst). Using a recent theory prediction for [B(B(s)(0)_J/__)/B(B(d)(0)_J/_K(*0))] yields (f(s)/f(d))=0.240±0.004(stat)±0.010(syst)±0.017(th). This result is based on a new approach that provides a significant improvement of the world average.