Measurement of the fraction of \Y1S originating from \chib1P decays in $pp$ collisions at $\sqrt{s} = 7\tev$

The production of \chib1P mesons in pp collisions at a centre-of-mass energy of $7\tev$ is studied using $32\invpb$ of data collected with the \lhcb detector. The $\chib1P$ mesons are reconstructed in the decay mode $\chib1P \to \Y1S\g \to \mumu\g$. The fraction of \Y1S originating from \chib1P decays in the \Y1S transverse momentum range $6 < \pt^{\Y1S} < 15\gevc$ and rapidity range $2.0 < y^{\Y1S} < 4.5$ is measured to be (20.7±5.7±2.1+2.7−5.4), where the first uncertainty is statistical, the second is systematic and the last gives the range of the result due to the unknown \Y1S and \chib1P polarizations.