Limits on the Production of Narrow t-tbar Resonances in p-pbar Collisions at sqrt(s)=1.96 TeV

Abstract

We search for evidence of resonant top quark pair production in 955 pb-1 of p-pbar collisions at sqrt(s)=1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate t-tbar events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of t-tbar pairs to the expected superposition of standard model t-tbar, non-t-tbar backgrounds, and a simple resonance model based on a sequential Z' boson. We establish upper limits for sigma(p-pbar to Z') times Br(Z' to t-tbar) in the Z' mass interval from 450 GeV/c2 to 900 GeV/c2. A topcolor leptophobic Z' is ruled out below 720 GeV/c2, and the cross section of any narrow Z'-like state decaying to t-tbar is found to be less than 0.64 pb at 95% C.L. for M(Z') above 700 GeV/c2.

Figures (3)

• Figure 1: Simulated $M_{t\bar{t}}$ spectrum for 955 ${\rm pb}^{-1}$ in presence of a 750 $\rm GeVc^2 GeV$/c^2$~Z'$ with $\sigma B= 1$ pb (shaded curve). The points are a simulated data set. The solid line is the best fit to a superposition of the $Z'$ signal (solid histogram) and the expected $t\bar{t}$ (dot) and non-$t\bar{t}$ (dot-dash) backgrounds. The inset shows a magnified view of the reconstructed $M_{t\bar{t}}$ spectrum for a 750 $\rm GeVc^2 GeV$/c^2$$$Z'$. The low mass tail arises from incorrect jet-parton associations.
• Figure 2: The invariant mass of top quark pairs $M_{t\bar{t}}$ observed in the data is compared to the no $Z'$ expectation. The non-$t\bar{t}$ backgrounds are constrained to the expected value and the sum of $t\bar{t}$ and non-$t\bar{t}$ equal the number of data events.
• Figure 3: Upper limits (95% C.L.) on the production cross section for $t\bar{t}$ resonance along with expected cross sections for several models.