Combined search for the standard model Higgs boson decaying to b bbar using the D0 Run II data set

TL;DR

The results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into bb using the data sample collected with the D0 detector in pp collisions at the Fermilab Tevatron Collider are presented.

Abstract

We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into b bbar using the data sample collected with the D0 detector in p pbar collisions at sqrt{s}=1.96 TeV at the Fermilab Tevatron Collider. We derive 95% CL upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100 GeV <= M_H <= 150 GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% CL. In the mass range 120 GeV <= M_H <= 145 GeV the data exhibit an excess above the background prediction with a global significance of 1.5 standard deviations, consistent with the expectation in the presence of a standard model Higgs boson.

Figures (3)

• Figure 1: (color online). Background-subtracted data distributions of $\log_{10}(s/b)$ in (a) the $VZ$ analysis after a fit of the $VZ$ and background contributions to the data and (b) the $VH$, $H\to b\bar{b}$ search for $M_H = 125\mathrm{~Ge V} \textrm{~Ge V}$ after a fit of the backgrounds to the data. The background-subtracted data are shown as points and the signal is shown as the red histogram in each plot. The blue lines indicate the posterior uncertainty on the background prediction.
• Figure 2: (color online). (a) The 95% C.L. cross section upper limit ratios versus $M_H$, and (b) LLR distribution versus $M_H$, for the combined $VH$, $H\to b\bar{b}$ analyses. The solid lines represent the observed values in the data. The short-dashed black (red) lines represent the median expected values under the background-only (signal-plus-background) hypothesis at each mass. The long-dashed blue lines show the expected outcome from injecting a SM Higgs boson signal with $M_H=125$Ge V. The green and yellow shaded bands correspond to the regions enclosing 1 and 2 s.d. variations about the median expected values under the background-only hypothesis, respectively.
• Figure 3: (color online). The best-fit value for $\sigma(VH) \times {\rm BR}(H\to b\bar{b})$ as a function of $M_H$. The green shaded band corresponds to the 1 s.d. uncertainty around the best-fit cross section. Also shown is the SM prediction including the theoretical uncertainties.