  A study of proton-proton collisions in which two b hadrons are produced in
association with a Z boson is reported. The collisions were recorded at a
centre-of-mass energy of 7 TeV with the CMS detector at the LHC, for an
integrated luminosity of 5.2 inverse femtobarns. The b hadrons are identified
by means of displaced secondary vertices, without the use of reconstructed
jets, permitting the study of b-hadron pair production at small angular
separation. Differential cross sections are presented as a function of the
angular separation of the b hadrons and the Z boson. In addition, inclusive
measurements are presented. For both the inclusive and differential studies,
different ranges of Z boson momentum are considered, and each measurement is
compared to the predictions from different event generators at leading-order
and next-to-leading-order accuracy.
