Probing stops in the coannihilation region at the HL-LHC: a comparative study of different processes

TL;DR

This study compares different processes at the HL-LHC to probe stops in the coannihilation region, finding that combined searches can extend sensitivity to dark matter masses up to about 1.1 TeV.

Contribution

It provides a comprehensive analysis of multiple production channels for stops and sbottoms, highlighting their complementary roles in probing the coannihilation region at the HL-LHC.

Findings

Sensitivity to dark matter mass can reach up to 570 GeV via stop pair production plus jet.

Sensitivity can reach up to 600 GeV via stop pair production.

Sensitivity can reach up to 1.1 TeV via sbottom pair production.

Abstract

In the minimal supersymmetric model, the coannihilation of the lighter stop $\tilde{t}_1$ and bino-like dark matter $\chi$ provides a feasible way to accommodate the correct dark matter relic abundance. In this scenario, due to the compressed masses, $\tilde{t}_1$ merely appears as missing energy at the LHC and thus the pair production of $\tilde{t}_1$ can only be probed by requiring an associated energetic jet. Meanwhile, since $\tilde{t}_2$ and $\tilde{b}_1$ are correlated in mass and mixing with $\tilde{t}_1$, the production of $\tilde{t}_2\tilde{t}_2^*$ or $\tilde{b}_1\tilde{b}_1^*$, each of which dominantly decays into $\tilde{t}_1$ plus $Z$, $h$ or $W$ boson, may serve as a complementary probe. We examine all these processes at the HL-LHC and find that the $2\sigma$ sensitivity to $\chi$ mass can be as large as about 570 GeV, 600 GeV and 1.1 TeV from the production process of $\tilde{t}_1\tilde{t}_1^*+{\rm jet}$, $\tilde{t}_2\tilde{t}_2^*$ and $\tilde{b}_1\tilde{b}_1^*$, respectively.