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

TL;DR

This study measures the flavor composition of dijet events in proton-proton collisions at 7 TeV using ATLAS data, providing insights into jet flavor fractions and testing QCD predictions.

Contribution

It introduces a multidimensional template fit method for identifying jet flavors and compares measured fractions with theoretical calculations.

Findings

Agreement with leading- and next-to-leading-order predictions for most flavor combinations.

Underestimation of bottom-light jet fractions at high transverse momentum.

Demonstration of identifying jets with two b-hadrons from gluon splitting.

Abstract

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 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.