Combined search for the standard model Higgs boson decaying to a bb pair using the full CDF data set

Abstract

We combine the results of searches for the standard model Higgs boson based on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar collisions at the Fermilab Tevatron corresponding to an integrated luminosity of 9.45/fb. The searches are conducted for Higgs bosons that are produced in association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and decay into bb pairs. An excess of data is present that is inconsistent with the background prediction at the level of 2.5 standard deviations (the most significant local excess is 2.7 standard deviations).

Figures (4)

• Figure 1: Background-subtracted distributions for the discriminant histograms, summed for bins with similar signal-to-background ratio ($s/b$), for the diboson search (top) and the $H\rightarrow b{\bar{b}}$$(m_H=125$ GeV/$c^2)$ search (bottom). The background has been fit to the data, and the uncertainty on the background is the post-fit uncertainty. The signal model, which is normalized to the SM expectation, is shown with a filled histogram. The uncertainty on the background-subtracted data points shown is the square root of the post-fit background prediction in each bin. The leftmost bin contains all events of lower $s/b$ values.
• Figure 2: Observed and expected 95% C.L. upper limits on SM Higgs boson production (R$_{95}$) as a function of Higgs boson mass. The shaded bands indicate the credibility bands in which $R_{95}$ is expected to fluctuate, in the absence of signal.
• Figure 3: The best-fit cross section times branching ratio $(\sigma_{WH}+\sigma_{ZH})\times \mathcal{B}(H\rightarrow b{\bar{b}})$ as a function of $m_H$. The dark-shaded region shows the one standard deviation C.L. band, the light-shaded region shows the two standard deviation C.L. region, and the SM prediction is shown as the smooth, falling curve with a narrow band indicating the theoretical uncertainty.
• Figure 4: Background-only $p$-value for the combined search. Also shown are the median expected values and the one and two standard deviation C.L. bands assuming a SM signal is present, evaluated at each $m_H$ separately.