Search for the Higgs Boson Produced in Association with $Z\to {\ell }^{+}{\ell }^{-}$ in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a search for the Higgs boson in the process $q\overline{q}\to ZH\to {\ell }^{+}{\ell }^{-}b\overline{b}$. The analysis uses an integrated luminosity of $1{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions produced at $\sqrt{s}=1.96\mathrm{TeV}$ and accumulated by the upgraded Collider Detector at Fermilab (CDF II). We employ artificial neural networks both to correct jets mismeasured in the calorimeter and to distinguish the signal kinematic distributions from those of the background. We see no evidence for Higgs boson production, and set 95% C.L. upper limits on ${\sigma }_{ZH}\mathcal{B}(H\to b\overline{b}$), ranging from 1.5 to 1.2 pb for a Higgs boson mass ($m_H$) of 110 to $150\mathrm{GeV}/c^2$.

Figure 1

Expected and observed distributions for the three most important inputs to the signal discriminating ANN shown after ANN jet corrections have been applied, for events with 1 $b$ tag.

Figure 2

Expected and observed distributions for the ANN discriminant projected onto the axis which discriminates $Z+\mathrm{\text{jets}}$ from $ZH$, after enriching signal by selecting the most signal-like 25% of events as determined by the $t\overline{t}$ vs $ZH$ ANN output. The top plot is the ANN discriminant before $b$-tagging requirements, demonstrating two models for the $Z+\mathrm{\text{jets}}$ background normalized to data for shape comparison. The middle and lower plots are for single-tagged and double-tagged events, and are shown with a $ZH$ signal at the level of the observed 95% C.L. upper limit for $m_H=120\mathrm{GeV}/c^2$.