Measurement of the b-tag Efficiency in a Sample of Jets Containing Muons with 5 fb−1 of Data from the ATLAS Detector

The efficiency of several $b$-tagging algorithms has been measured with two methods using data from the ATLAS detector. The measurements are based on a sample of jets containing muons and are based on 5 fb^{-1} of data collected in 2011. The measurements of the b-tag efficiency are provided in the form of jet-pT dependent scale factors that correct the b-tagging performance in simulation to that observed in data. Good consistency is observed between the results of the two methods. The b-tag efficiency scale factors are found to be about 10% below unity for most tagging algorithms and operating points, but become consistent with unity for the loosest operating points, corresponding to the highest b-tagging efficiencies. The precision of the measurement depends on the calibration method, tagging algorithm, operating point and jet-pT bin. For the highest performance MV1 tagging algorithm at an operating point corresponding to a 70% b-tag efficiency in a ttbar sample, the total uncertainty ranges from 5% to 19%, with the largest uncertainties corresponding to the highest pT bins.