Calibration of the b-tagging efficiency on jets with charm quark for the ATLAS experiment

The correct identification of jets originated from a beauty quark (b-jets) is of fundamental importance for many physics analysis performed by the ATLAS experiment, operating at the Large Hadron Collider, CERN. The efficiency to mistakenly tag a jet originated from a charm quark (c-jet) as a b-jet has been measured in data with two different methods: a first one, referred as the "D* method", uses a sample of jets containing reconstructed D* mesons (adopted for 7 TeV and 8 TeV data analyses), and a second one, referred as the "W+c method", uses a sample of c-jets produced in association with a W boson (studied on 7 TeV data). This thesis work focuses on some significant improvements made to the D* method, increasing the measurement precision. A study for the improvement of the W+c method and its first application to 13 TeV data is also presented: focusing on the event selection, the W+c signal yield has been considerably increased with respect to the background processes