A short comparison between m_T2 and m_CT
  We compare m_T2 with m_CT; both are kinematic variables designed to find relationships between masses of pair-produced new states with symmetric decay chains. We find that for massless visible particles m_CT equals m_T2 in a particular limit. We identify advantages and disadvantages to the use of each variable. Tovey's paper on m_CT also introduced a powerful concept of extracting mass information from an analysis at intermediate stages of a symmetric decay chain. We suggest that m_T2 is a better tool for performing this analysis than m_CT due to m_T2's better properties under initial state radiation. 
Mario Serna