Heavy Flavor Simplified Models at the LHC

TL;DR

The paper develops a comprehensive framework for searching heavy-flavor new physics at the LHC using a set of twelve simplified models based on pair-produced color octets or triplets decaying to top/bottom quarks and a stable neutral particle. It maps out a wide space of signatures, then employs a genetic algorithm to identify a minimal but near-optimal set of search regions that cover the model space with high efficacy, highlighting the crucial roles of 3b and same-sign dilepton channels, especially at higher luminosities. The authors provide benchmark models and re-optimized search strategies to guide experimental analyses, quantify expected limits against existing ATLAS searches, and show that a small number of regions can achieve broad coverage. The work offers a practical methodology for experimental optimization and demonstrates how targeted channels can substantially enhance sensitivity to heavy-flavor new physics at the LHC.

Abstract

We consider a comprehensive set of simplified models that contribute to final states with top and bottom quarks at the LHC. These simplified models are used to create minimal search strategies that ensure optimal coverage of new heavy flavor physics involving the pair production of color octets and triplets. We provide a set of benchmarks that are representative of model space, which can be used by experimentalists to perform their own optimization of search strategies. For data sets larger than 1/fb, same-sign dilepton and 3b search regions become very powerful. Expected sensitivities from existing and optimized searches are given.

Figures (17)

• Figure 1: Gluino-like simplified models used in this study. $\mathcal{G}_{\tilde{B}}$ models have only a light 'bino'-like state, while $\mathcal{G}_{\tilde{W}}$ models have an additional charged state. The charged state is always nearly degenerate with a neutral state, so that there are not any additional visible leptons from its decay.
• Figure 2: Squark-like simplified models used in this study.
• Figure 3: Feynman Diagrams for $t+nj$ and $t+W+nj$. Notice the need to subtract the on-shell top contribution from $t W \bar{b}$ sample.
• Figure 4: The effect of matching is shown for a signal with a $\tilde{g}$ at 400 GeV and a $\chi^0$ at 390 GeV in the $\mathcal{G}_{\tilde{B}} ^{\tt BB}$ simplified model. The left plot shows the $p_T$ spectrum of the leading jet. The right plot shows the effect on the jet multiplicity.
• Figure 5: NLO cross sections for gluinos and third generation squarks, with other squarks decoupled.