Search for ttbar resonances in the lepton plus jets final state in ppbar collisions at sqrt{s}=1.96TeV

TL;DR

This work searches for a narrow-width resonance decaying to $t\overline{t}$ in $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV using $\approx0.9\ \mathrm{fb}^{-1}$ with the D0 detector, focusing on the lepton+jets final state and requiring $b$-tagging. The $t\overline{t}$ invariant mass is reconstructed to identify resonant contributions, with signal and SM backgrounds modeled via MC simulations and data-driven techniques; a Bayesian framework sets 95% C.L. upper limits on $\sigma_X\cdot B(X\rightarrow t\overline{t})$ across $M_X$ from 350 to 1000 GeV, and the results exclude a leptophobic $Z'$ in a Topcolor-assisted technicolor scenario for $M_{Z'}<700$ GeV with $\Gamma_{Z'}=0.012\,M_{Z'}$. No evidence for a resonance is observed, and the limits provide constraints on TeV-scale resonances coupling to top quark pairs. The analysis demonstrates the power of invariant-mass reconstruction in the lepton+jets channel and establishes important bounds on beyond-Standard-Model top quark resonance scenarios at the Tevatron. The findings have implications for models predicting heavy $t\overline{t}$ resonances and guide future searches at hadron colliders.

Abstract

We present a search for a narrow-width heavy resonance decaying into top quark pairs X->ttbar in ppbar collisions at sqrt{s}=1.96TeV using approximately 0.9fb^-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. This analysis considers ttbar candidate events in the lepton plus jets channel with at least one identified b jet and uses the ttbar invariant mass distribution to search for evidence of resonant production. We find no evidence for a narrow resonance X decaying to ttbar. Therefore, we set upper limits on sigma*B(X->ttbar) for different hypothesized resonance masses using a Bayesian approach. For a Topcolor-assisted technicolor model, the existence of a leptophobic Z' boson with mass M_Z'<700GeV and width Gamma_Z'=0.012 M_Z' can be excluded at the 95% C.L.

Figures (3)

• Figure 1: Shape comparison of the expected $t\overline{t}$ invariant mass distributions for SM top quark pair production (histogram) and resonant production from narrow-width resonances of mass $M_X=450$, $650$, and $1000\,\hbox{GeexV}\xspace$, for (a) $3$ jets events and (b) $\ge 4$ jets events.
• Figure 2: Expected and observed $t\overline{t}$ invariant mass distribution for the combined (a) $\ell+3$ jets and (b) $\ell+4$ or more jets channels, with at least one identified $b$ jet. Errors shown on the data points are statistical. Superimposed as white area is the expected signal for a Topcolor-assisted technicolor $Z'$ boson with $M_{Z'}=650\,\hbox{GeexV}\xspace$.
• Figure 3: Expected and observed 95$\%$ C.L. upper limits on $\sigma_{X}\!\cdot\! B(X\!\rightarrow\!t\overline{t}\xspace)$ compared with the predicted Topcolor-assisted technicolor cross section for a $Z'$ boson with a width of $\Gamma_{Z'} = 0.012 M_{Z'}$ as a function of resonance mass $M_{X}$. The shaded band gives the $\pm$1 sigma uncertainty in the SM expected limit.