Hamburg 2016 – scientific programme

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T: Fachverband Teilchenphysik

T 74: Experimentelle Methoden II

T 74.6: Talk

Wednesday, March 2, 2016, 18:00–18:15, VMP8 SR 105

Calibration of the light-jet fraction in b -tagging algorithms for the ATLAS detector in Run 2 of the LHC — Alexander Mann and •Balthasar Schachtner — LMU München

B-tagging algorithms have, depending on the working point used, a small probability to tag a light jet as a b -jet. This mistag-rate can be determined using the “negative-tag method” and allows to derive data-to-Monte-Carlo scale factors.

To tag jets originating from b -quarks, ATLAS has developed a new multivariate algorithm (MV2c20) for Run 2. The input variables are designed to exploit the finite decay length of b -hadrons and the event kinematics. Assuming that light jets are tagged as b -jets mainly due to the finite resolution of the detector, lifetime-based variables used in the algorithm will be symmetric with respect to the primary vertex. A “negative” version of the algorithm with all lifetime-based variables inverted is defined to obtain an estimate of the fraction of light jets tagged as b -jets due to resolution effects.

For the calculation of the data-to-Monte-Carlo scale factors, corrections need to be applied and are derived from Monte Carlo. The correction factors account for the heavy-flavour contribution and asymmetries in the positive and negative tagging due to decays of long-lived particles and conversions in the detector.