Abstract
This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at \(\sqrt{s} =7\mbox {~TeV}\) using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions 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 bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions.
Highlights
Several mechanisms contribute to heavy flavour quark production, such as quark–antiquark pair creation in the hard interaction or in the parton showering process
In inclusive heavy flavour jet cross-sections, the contribution from gluon splitting in the final state parton showering could be identified by looking for two heavy flavour hadrons in a jet, but the different mechanisms for prompt heavy flavour quark production in the hard interaction remain indistinguishable
Following the discussion in [35], heavy flavour quark production in hadronic collisions may be subdivided into three classes depending on the number of heavy quarks participating in the hard scattering
Summary
Several mechanisms contribute to heavy flavour quark production, such as quark–antiquark pair creation in the hard interaction or in the parton showering process. In inclusive heavy flavour jet cross-sections, the contribution from gluon splitting in the final state parton showering could be identified by looking for two heavy flavour hadrons in a jet, but the different mechanisms for prompt heavy flavour quark production in the hard interaction remain indistinguishable. This complicates a comparison with theoretical calculations. A more exclusive study of the production of dijet events containing heavy flavour jets allows the different prompt heavy flavour quark creation processes to be separated, in addition to the gluon splitting contribution.
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