Measurement of the flavour composition of dijet events in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at sqrt(s)=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39pb^1. Six possible combinations of light, charm and beauty jets in the dijet events are identified, where the jet flavour is defined by the presence of beauty, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimized for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijets flavour states as a function of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y| < 2.1. The fit results agree with the predictions of leading and next-to-leading order calculations, with the exception of the dijet fraction composed of beauty and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originated from e.g. gluon splitting, is demonstrated.The difference between beauty jet production rates in leading and subleading jets is consistent with the next-to-leading order prediction.