2011 QCD and High Energy Interactions - Rencontres de Moriond ...

95% CL Limit/SM
10
1
Tevatron Run II Preliminary, = 5.9 fb -1
LEP Exclusion Tevatron
Exclusion
SM=1
Expected
Observed
±1σ Expected
±2σ Expected
Tevatron Exclusion July 19, 2010
100 110 120 130 140 150 160 170 180 190 200
mH (GeV/c 2 )
Figure 1: Left: Limits at the 95% CL on the cross section for a SM Higgs boson from the Tevatron as of July 2010.
Right: The projected Tevatron 95% CL exclusion and 3σ evidence sensitivity to SM Higgs boson production as
a function of Higgs boson mass (mH) and delivered luminosity to each experiment. The shaded regions indicate
the expected sensitivity gain through analysis improvements.
Figure 2: Left: Event selection efficiency in the CDF ZH → µµbb analysis increases substantially for low muon
pT events when moving to a more inclusive trigger suite. Right: Distribution of the minimum ∆R between a
muon and jet after using a neural network based event selection, with inset plots showing dimuon invariant mass
for events that pass and fail the previous analysis cut of ∆R > 0.4.
allows for the recovery of signal-like events where ∆R between a muon and a jet is below the
previous cut threshold. a Together, these improvements help this analysis gain 25% improvement
in the expected 95% CL limit at mH = 115 GeV beyond the expected gain due to additional
integrated luminosity when compared to its previous iteration.
Including more Higgs boson decay channels in the Tevatron combination helps improve our
expected sensitivity by effectively adding extra signal acceptance to our overall search. Analyses
at both CDF and D0 focus on Higgs decays that include both a hadronic tau decay (τh) and
an electron or muon. This hadronic plus leptonic channel account for 46% of all ττ decays. It
also includes contributions from both direct and associated production modes and many decay
modes, leading to relatively consistent sensitivity at all mH, as shown in Figure 3. The latest
iteration of the D0 analysis added the eτh channel to the previous µτh-only analysis and improved
the expected sensitivity at mH = 115 GeV by 15% beyond improvements due to the additional
integrated luminosity.
For the low-mass associated production channels, discriminating the b-quark jet signature
of a potential Higgs boson signal from the large background of light-quark multijet events is a
key element of each analysis. Selecting events with one or two candidate b-jets substantially
improves the signal to background ratio, as shown in Figure 4. At D0, recent improvements
a ∆R = √ ∆ϕ 2 + ∆η 2 between two objects, where pseudorapidity η = − ln [tan( θ
2 )] and θ is the angle between
a particle and the beam axis.