Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2008-03-27
JHEP 0905:117,2009
Physics
High Energy Physics
High Energy Physics - Phenomenology
22 pages,16 figures
Scientific paper
10.1088/1126-6708/2009/05/117
We study methods of extracting new physics signals in final states with a top-quark pair plus large missing energy at the LHC. We consider two typical examples of such new physics: pair production of a fermionic top partner (a $T'$ in Little Higgs models for example) and of a scalar top partner (a $\tilde{t}$ in SUSY). With a commonly-adopted discrete symmetry under which non Standard Model particles are odd, the top partner is assumed to decay predominantly to a top quark plus a massive neutral stable particle $A^0$. We focus on the case in which one of the top quarks decays leptonically and the other decays hadronically, $pp \to {\tt} A^0A^0 X \to bj_1j_2 \bar b\ell^- \bar\nu A^0A^0 X + c.c.$, where the $A^0$s escape detection. We identify a key parameter for the signal observation: the mass splitting between the top partner and the missing particle. We reconstruct a transverse mass for the lepton-missing transverse energy system to separate the real $W$ background from the signal and propose a definition for the reconstructed top quark mass that allows it to take unphysical values as an indication of new physics. We perform a scan over the two masses to map out the discovery reach at the LHC in this channel. We also comment on the possibility of distinguishing between scalar and fermionic top partners using collider signatures.
Han Tao
Mahbubani Rakhi
Walker Devin G. E.
Wang Lian-Tao
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