Measurement of the Azimuthal Correlation in b-bbar Production in pp Collisions with the CMS detector

We present an analysis aimed at the measurement of the azimuthal angular correlation of $b\bar{b}$ production. We use $b\bar{b} \to (J/\psi X)( \ell X')$ events, where the charged lepton is a muon, to measure the azimuthal opening angle $\Delta\phi$ between the bottom quarks. The $b\bar{b}$ purity is determined as a function of $\Delta\phi$ by a simultaneous fit to the $J/\psi$ invariant mass and decay length, and the lepton impact parameter.