Search for standard-model Z and Higgs bosons decaying into a bottom-antibottom quark pair in proton-antiproton collisions at 1.96 TeV

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Abstract

The Collider Detector at Fermilab collected a unique sample of jets originating from bottom-quark fragmentation ($b$-jets) by selecting online proton-antiproton ($p\overline{p}$) collisions with a vertex displaced from the $p\overline{p}$ interaction point, consistent with the decay of a bottom-quark hadron. This data set, collected at a center-of-mass energy of 1.96 TeV, and corresponding to an integrated luminosity of $5.4\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, is used to measure the $Z$-boson production cross section times branching ratio into $b\overline{b}$. The number of $Z\ensuremath{\rightarrow}b\overline{b}$ events is determined by fitting the dijet-mass distribution, while constraining the dominant $b$-jet background, originating from QCD multijet events, with data. The result, $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}Z)\ifmmode\times\else\texttimes\fi{}\mathcal{B}(Z\ensuremath{\rightarrow}b\overline{b})=\phantom{\rule{0ex}{0ex}}1.11\ifmmode\pm\else\textpm\fi{}0.08(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.14(\mathrm{syst})\text{ }\text{ }\mathrm{nb}$, is the most precise measurement of this process, and is consistent with the standard-model prediction. The data set is also used to search for Higgs-boson production. No significant signal is expected in our data and the first upper limit on the cross section for the inclusive $p\overline{p}\ensuremath{\rightarrow}H\ensuremath{\rightarrow}b\overline{b}$ process at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ is set, corresponding to 33 times the expected standard-model cross section, or $\ensuremath{\sigma}=40.6\text{ }\text{ }\mathrm{pb}$, at the 95% confidence level.

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