Updated Combination of CDF and D0 Searches for Standard Model Higgs Boson Production with up to 10.0 fb-1 of Data
We combine results from the CDF and D0 Collaborations on direct searches for the standard model (SM) Higgs boson (H) in ppbar collisions at the Fermilab Tevatron at sqrt(s)=1.96 TeV. Compared to the previous Tevatron Higgs boson search combination, more data have been included, additional channels have been incorporated, and some previously used channels have been reanalyzed to gain sensitivity. Searches are carried out for hypothesized Higgs boson masses between 100 and 200 GeV/c^2. With up to 10 fb-1 of luminosity analyzed, the 95% C.L. median expected upper limits on Higgs boson production are factors of 0.89, 1.08, and 0.48 times the values of the SM cross section for Higgs bosons of mass m_H=115 GeV/c^2, 125 GeV/c^2, and 165 GeV/c^2, respectively. In the absence of signal, we expect to exclude the regions 100<m_{H}<120 GeV/c^2 and 139<m_H<184 GeV/c^2. We exclude, at the 95% CL, two regions: 100<m_H<103 GeV/c^2, and 147<m_H<180 GeV/c^2. There is a significant excess of data events with respect to the background estimation in the mass range 115<m_H<140 GeV/c^2, which causes our observed limits to not be as stringent as expected. At m_H=120 GeV/c^2, the p-value for a background fluctuation to produce this excess is \sim1.5x10^-3, corresponding to a local significance of 3.0 standard deviations. The global significance for such an excess anywhere in the full mass range investigated is approximately 2.5 standard deviations. We also combine separately searches for H to bb and H to WW. We find that the excess is concentrated in the H to bb channel, appearing in the searches over a broad range of m_H. The maximum local significance of 3.2 standard deviations corresponds to a global significance of approximately 2.9 standard deviations. Our results in the H to WW channels are also consistent with the possible presence of a low-mass Higgs boson.