Discovering Heavy New Physics in Boosted $Z$ Channels: $Z\to l^{+}{l}^{-}$ vs. $Z\to \nu \bar{\nu }$

Abstract

We propose a strategy for new physics searches in channels which contain a boosted $Z$ boson in the final state. Our proposal exploits the previously overlooked advantages of boosted $Z\to \nu \bar{\nu }$ topologies, where collimated neutrinos result in signals with large missing energy. We illustrate the advantage of this channel in a case study of singly produced TeV scale charge 2/3 fermionic top partners ($T^{\prime }$) which decay to $t+Z$. A comparison with the di-leptonic channel reveals that signals with missing energy offer superior probes of new physics at TeV scales, despite the large $t\bar{t}$ backgrounds. The effect can be attributed to a factor of $\sim 3$ enhancement in the signal cross section, coming from the branching ratio of $Z\to \nu \bar{\nu }$. We exploit the unique event topology of singly produced top partners to suppress the $t\bar{t}$ background, as well as further improve on the existing proposals to detect $T^{\prime }$ in the boosted di-lepton channel. Our conclusions on advantages of $Z\to \nu \bar{\nu }$ can be extended to most physics searches which utilize a boosted $Z$ boson in the final state.

Comments: Fig. 2 added, typos fixed, references added, version corresponds to version published in PRD