Recent results on vector-like quarks and excited fermions at CMS

TL;DR

The CMS study investigates vector-like quarks and excited fermions with the full Run 2 dataset at $\sqrt{s}=13$ TeV and $138~\mathrm{fb}^{-1}$, finding no deviations from the Standard Model. It reports improved exclusion limits across multiple decay channels, including $T \to bW$, $T \to tH$, $T \to tZ$, and exotic decays $T \to t\phi$, as well as excited top decays $t^*\to tg$ and $t^*\to t\gamma$. The analysis employs advanced techniques—ParticleNet-MD, boosted top tagging, 2D maximum-likelihood fits in $(m_T,m_\phi)$, and decorrelated DNN discriminants—to enhance sensitivity relative to earlier CMS results. Collectively, these results place stringent constraints on TeV-scale top partners in composite Higgs and top compositeness models, guiding future searches and model-building efforts at the LHC.

Abstract

The most recent results on the searches for the vector-like quarks and excited fermions from the CMS Collaboration are presented. These results are based on the full Run 2 $\sqrt{s} = $13 TeV proton-proton collision data collected by the CMS Collaboration at the LHC from 2016 to 2018, which corresponds to an integrated luminosity of 138 fb$^{-1}$. No significant excess above the Standard Model expectation is observed. Exclusion limits are set at the 95% confidence level on various benchmark models.

Figures (8)

• Figure 1: Observed 95% CL upper limits on the single T quark production cross section times the branching fraction of T $\to$ t$\phi$$\to$ b$l \nu \mathrm{b \overline{b}}$ as a function of T mass and $\phi$ mass. Figure from Ref. b2g-23-009
• Figure 2: Observed (solid black line) and expected (dashed line) 95% CL upper limits on the single T quark production cross section times the branching fraction of T $\to$ tH. Figure from Ref. b2g-23-009
• Figure 3: Pull in the reconstructed $\phi$ mass and T mass in the signal region after maximum likelihood fit to the data. Figure from Ref. CMS-PAS-B2G-22-001
• Figure 4: Median expected (left) and observed (right) upper limits at the 95% CL on the product of the T $\to$ t$\phi$ production cross section and the branching fraction $\mathcal{B}(\mathrm{t \to b q \overline{q}})$ as a function of T mass and $\phi$ mass. Figure from Ref. CMS-PAS-B2G-22-001
• Figure 5: Upper limits at 95% CL on the product of the production cross section of T $\to$ tH and $\mathcal{B}$(T $\to$ tH) as a function of T mass for $\phi$(H) mass 125 GeV. Figure from Ref. CMS-PAS-B2G-22-001