Search for standard model Higgs boson production in association with a $W$ boson using a neural network discriminant at CDF

We present a search for standard model Higgs boson production in association with a $W$ boson in proton-antiproton collisions ($p\overline{p}\to W^{\pm }H\to \ell \nu b\overline{b}$) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector that correspond to an integrated luminosity of approximately $1.9{\mathrm{fb}}^{-1}$. We select events consistent with a signature of a single charged lepton ($e^{\pm }/{\mu }^{\pm }$), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method, a jet probability tagging method, and a neural network filter. We use kinematic information in an artificial neural network to improve discrimination between signal and background compared to previous analyses. The observed number of events and the neural network output distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching fraction ranging from 1.2 to 1.1 pb or 7.5 to 102 times the standard model expectation for Higgs boson masses from 110 to $150\mathrm{GeV}/c^2$, respectively.

Figure 1

The total acceptance $ϵ$ for the process $WH\to \ell \nu b\overline{b}$ in $W+2$ jet bin for the selected $b$-tagging strategies as a function of Higgs boson mass.

Figure 2

Number of events in the central and plug regions are shown as a function of jet multiplicity for events with exactly one secvtx $b$-tag applying the NN $b$-tagging filter (left) and for events with at least two secvtx $b$-tagged jets or one secvtx $b$-tagged jet plus one jet probability $b$-tagged jet (right).

Figure 3

Neural Network output distribution in $W+2$ jets events for exactly one secvtx $b$-tagged jet that passes the NN $b$-tagging filter (left) and events for $\mathrm{ST}+\mathrm{ST}$ and $\mathrm{ST}+\mathrm{JP}$ double $b$-tagging categories (right). The contributions of the various background sources from the central plus plug region are shown in histograms while the hatched box represents the background uncertainty. The expected signal for a 120 GeV Higgs boson (multiplied by a factor of 10) is shown by the solid line.

Figure 4

The observed (solid) and expected (dashed) 95% confidence level upper limit on $\sigma (p\overline{p}\to WH)·\mathcal{B}(H\to b\overline{b})$ relative to the standard model expectations with an integrated luminosity of $1.9{\mathrm{fb}}^{-1}$ along with the one and two $\sigma$ bands of the distributions of expected outcomes from pseudoexperiments.