Understanding and improving the Effective Mass for LHC searches

Understand

A handy and extensively used kinematic variable in LHC analyses, especially for golden SUSY signals of multijets plus missing energy, is the Effective Mass, M_eff = sum_j |p_T^j|+ |p_T^miss|.

• Empirically, the value of M_eff at which the histogram of events has a maximum is correlated with the SUSY spectrum, M_eff|_max ~ 80% M_susy, where M_susy is essentially the sum of the masses of the SUSY particles initially created.
• In this paper we explain the reason for such strong correlation, pointing out the cases where the correlation is not good.
• Besides, we propose a new variable, the Effective Transverse Energy, E_T^eff, which shows an even better and more direct correlation E_T^eff|_max ~ M_susy, and is independent of the procedure followed to identify the jets.