Measurement of the top quark mass in the $t\bar{t} \to $ dilepton decay channel using the $m_{T2}, m_{T2\perp}$ and $m_{lb}$ variables with ATLAS data

A measurement of the top quark mass is studied in the ttbar dilepton decay channel. Three different variables: m_T2, m_T2perp and m_lb are used in this study. The m_T2 and m_T2perp are applied to solve the challenge of the production of two neutrinos in this decay channel while the m_lb only focuses on the lepton-jet (lb) system. The calibration curve method is applied in the mass measurement, using the ATLAS data of 4.7/fb at sqrt(s) = 7 TeV collected in 2011. The purpose of the study is to reduce the uncertainty of the measurement. Two main analyses are presented. The baseline analysis corresponding to the standard selection measured the top quark mass with m_top = 173.6 +- 0.9 (stat.) +- 1.7 (syst.) GeV for m_T2, m_top = 173.8 +- 0.7 (stat.) +- 1.8 (syst.) GeV for m_T2perp and m_top = 173.2 +- 0.8 (stat.) +- 1.5 (syst.) GeV for m_lb. The analysis with the optimisation selection in order to optimise the uncertainty of the measurement obtained the final results of m_top = 175.1 +- 0.9 (stat.) +- 1.6 (syst.) GeV for m_T2, m_top = 174.1 +- 0.8 (stat.) +- 1.4 (syst.) GeV for mT2perp and m_top = 174.1 +- 0.9 (stat.) +- 1.3 (syst.) GeV for m_lb. Among the three variables used, the m_lb variable yields the result with the lowest uncertainty, which is consistent with a new ATLAS top-quark mass measurement in dileptonic decay channel released in 2013.