Search for New Particles Leading to Z+jets Final States in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV

TL;DR

This paper reports a search for new particles producing Z bosons plus jets in proton-antiproton collisions at 1.96 TeV, using data from the CDF II detector, and sets limits on fourth-generation quark masses.

Contribution

It introduces a data-driven background prediction method applicable to multi-jet analyses and applies it to set limits on fourth-generation quark masses.

Findings

No significant excess observed above background.

Excluded fourth-generation b' quark masses below 268 GeV/c^2.

Validated background prediction method with W+jets in top quark production.

Abstract

We present the results of a search for new particles that lead to a \Z boson plus jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 \ifb\ collected using \Z boson decays to $ee$ and $\mu\mu$ is used. We describe a completely data-based method to predict the dominant background from standard-model \Z+jet events. This method can be similarly applied to other analyses requiring background predictions in multi-jet environments, as shown when validating the method by predicting the background from $W$+jets in \ttbar production. No significant excess above the background prediction is observed, and a limit is set using a fourth generation quark model to quantify the acceptance. Assuming $BR(b' \to b\Z) = 100%$ and using a leading-order calculation of the $b'$ cross section, $b'$ quark masses below 268 $\gev/c^2$ are excluded at 95% confidence level.