RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

And the methods used to estimate instrumental

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: expected these channels have considerably less sensitivity than the WH channels because of the significantly lower signal cross section times branching fraction. 3. ZH ! bb and related final states The ZH ! bb final state has a production rate intermediate between the WH and ZH ! ‘‘bb final states. This final state also has a significant contribution from the process WH ! ‘bb in which the charged lepton ‘ escapes detection. This is particularly true for the case ‘ ¼  because the muon leaves very little energy in the calorimeter and thus results in event ET similar to that from Z !  decay. 6 Unlike either of the previously discussed final states, the ZH ! bb final state has no charged leptons from vector boson decay. This implies a significantly increased background from SM multijet events in which ET arises from 6 Events/0.05 10 Observed, 1 b-tag (a) Z+jets w/ ALPGEN Other 2 ZH(120 GeV/c ) @ 95% CL upper limit 2 10 110 120 130 140 150 160 Higgs Mass (GeV/c2) FIG. 56. Expected and observed limits for the CDF 1:0 fbÀ1 ZH ! ‘‘bb analysis. mismeasurement. This background is difficult to model from simulation, and analyses of this final state must develop techniques to measure it using data control samples. Both CDF (Aaltonen et al., 2008g) and D0 (Abazov et al., 2010a) published results in this final state. The two experiments developed different methods for controlling and estimating the multijet background. a. CDF search The CDF analysis uses a data sample corresponding to 6 1 fbÀ1 and begins with selection of events passing a ET trigger with level one ET > 25 GeV, a level two requirement 6 of two jet clusters having ET > 10 GeV, and a level three requirement of ET > 35 GeV. At least one of the level two 6 jets must also satisfy  < 1:1. The initial offline selection (‘‘pretag’’) requires events to have MET > 50 GeV and exactly two jets with ET > 20 GeV. One of the jets must have ET > 35 GeV, and the other must have ET > 25 GeV. Additionally, one of the jets must satisfy jj < 0:9, and the other jet must satisfy jj < 2:4. The two jets must also have Á > 1:0 rad, and events with high pT , isolated leptons are vetoed. Finally, at least one of the jets is required to have a secondary vertex b tag. " All nonmultijet backgrounds, tt, W þ jets, Z þ jets, and diboson production are modeled using simulated events. The Events/0.05 10 Observed, 2 b-tags (b) Z+jets w/ ALPGEN Other 2 ZH(120 GeV/c ) @ 95% CL upper limit 2 10 1 10-1 0 0.2 0.4 0.6 0.8 1 NN Projection (Z+jets vs ZH) σ (pp → ZH) × B(H → bb) (pb) 1 10 2 DO, 370-450 pb-1 10 95% C.L. upper limit ( --- expected limit) 1 10 -1 standard model 10 -2 100 110 120 130 140 150 2 Higgs Mass (GeV/c ) FIG. 55. NN distributions for the (a) single-tagged and (b) doubletagged samples from the CDF 1:0 fbÀ1 ZH ! ‘‘bb analysis. The 95% C.L. upper bound cross section is 19Â the SM prediction. Rev. Mod. Phys., Vol. 84,...
View Full Document

Ask a homework question - tutors are online