Search for new particles decaying into top quark-antiquark pairs in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A search for new particles decaying to top quark-antiquark pairs is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV. The data set recorded with the CMS detector between 2016 and 2018 is used, corresponding to an integrated luminosity of 138 fb$^{-1}$. Final states with 0, 1, and 2 leptons are analyzed, covering all decay modes of the top quark-antiquark pairs. Heavy Z' bosons with relative widths of 1, 10, and 30% are excluded for masses in the ranges 0.4$-$4.8, 0.4$-$6.2, and 0.4$-$7.4 TeV, respectively. A Kaluza$-$Klein gluon in the Randall$-$Sundrum model and a dark-matter mediator are excluded for masses between 0.5$-$5.5 and 1.0$-$4.2 TeV, respectively. These results set the most stringent limits to date for the considered models in the $\mathrm{t\bar{t}}$ final state. In addition, in the two-Higgs-doublet models, upper limits are set on the coupling strength modifier for scalar and pseudoscalar Higgs bosons with relative widths of 2.5, 10, and 25% in the mass range of 0.5$-$1.0 TeV.

Figures (17)

• Figure 1: Example Feynman diagrams at leading order for the production and decay of a spin-1 $\mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}}$ / $\mathup{{{g}}{} _{ {\text{KK}}} ^{ {}}}$ boson (left) and a scalar $\mathup{{{H}}{} _{ {}} ^{ {}}}$ or pseudoscalar $\mathup{{{A}}{} _{ {}} ^{ {}}}$ resonance (right).
• Figure 2: Illustration of the background estimation method. The data set is binned in the leading jet mass $m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ and in the reconstructed $\mathup{{{t}}{} _{ {}} ^{ {}}}$$\mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}}$ invariant mass $m_{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{}{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace}\xspace}$. Disjoint regions are defined according to whether $m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ lies inside or outside the top quark mass window and whether the subleading jet passes or fails the ${ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace\text{ tagging}$ requirement. A method based on control samples in data is used to estimate the QCD background in the signal region E from regions A, B, C, D, and F. The colored dotted points are shown for illustrative purposes only.
• Figure 3: Prefit data-to-simulation comparison of distributions in the all-hadronic channel for the mass of the leading ${ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace\text{ tagged}$ jet (left) and the reconstructed $\mathup{{{t}}{} _{ {}} ^{ {}}}$$\mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}}$ mass (right) in the central and forward categories combined, where both jets pass the ${ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace\text{ tagging}$ requirement. The QCD background is taken from simulation for comparison, whereas in the analysis it is estimated from data. No cut on the $m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ variable is applied.
• Figure 4: Reconstructed $m_{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{}{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace}\xspace}$ distributions in simulation in the all-hadronic channel for $\mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}}$ bosons with 1 and 30% relative widths, shown in the left and right panels, respectively. The signals correspond to $\mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}}$ boson masses of 2, 4, and 6$\,\text{Te\spaceV}$, where both jets pass the ${ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace\text{ tagging}$ requirement. Signals are normalized to a cross section of 1$\text{\,pb}$ and an integrated luminosity of 138$\,\text{fb}^{-1}$. No cut on the $m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ variable is applied.
• Figure 5: Postfit distributions in $m_{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{}{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace}\xspace}$ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ (upper) and high-$m_{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}$ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $\mathup{{{{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {\prime}}}$ boson signal with a relative width of 1% and a mass of 2$\,\text{Te\spaceV}$ is normalized to a cross section of 1$\text{\,pb}$ and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as $(\text{Data}-\text{Prediction})/\sigma$, where $\sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction.