1. First look of ME study on ttH(  bb) channel Univ. of Tokyo Y.Kataoka Feb.21.2003 @CERN

2. Previous Analysis (1)  We introduced modified   method to solve the Combinatorial BG.  In this method, we used   values based on mass information, likelihood output of angle information.  Reconstructed Higgs mass plot (MH=120GeV) ttbb BG is dominant. M bb 30fb -1

3. Details are in the previous talk (Dec.12,2002). Previous Analysis (2) (true comb.)  Number of events (30fb -1 ) Combinatorial BG Is still large

4. Matrix Element Study Modified  2 method is not effective to solve Combinatorial BG.  We start a new study based on “Matrix Element”. This ultimate method may solve the problems. Is it possible to improve the current result ?

5. Event Selection  Number of isolated lepton = 1 for electron, p T >25GeV, |  |<2.5 for muon, p T >20GeV, |  |<2.5  Number of light flavor jet >= 2 p T >20GeV, |  |<2.5 p T >40GeV for at least one jet  Number of b-jet = 4 p T >30GeV ( The same as the previous study ) Decay mode H  b b t  l b t  j j b

6. Matrix Element After the event selection,  we calculate an event weight: “-log(ME)”,  and use this weight to solve the Combinatorial BG. We can choose the most probable combination. Matrix element is calculated by Grace (2.2.0). Input: 4-vector of 8 final fermions (H  bb, t  j j b, t  l b )  80 diagrams and their interference

8. Detector Resolutions In order to take detector resolutions into accounts, we set Higgs, top, W decay widths to 20GeV (temporary). In the parton level, we check the outputs of grace. Blue line is distribution with natural decay width. Red line is distribution with smearing. If we have good energy resolution, we have very good performance. -log(ME) Small |ME| 2 Large |ME| 2 Wrong comb. Correct comb.

9. Parton Level Study First, we use the parton level 4-momenta of the ttH signal sample (MH=120GeV). 1. all partons are correctly assigned (red line) 2. b and b-bar exchanged (blue line) ME method has the power of discrimination between correct and wrong assignments. -log(ME) Wide widths are included for W, t, H

10. Detector Level Study Next, we use the observed 4-vectors (Atlfast output). 1. jets and leptons are correctly assigned (red line) 2. b and b-bar exchanged (blue line) -log(ME) The discrimination power is decreased.

11. Parton level study shows: ME method is powerful to discriminate Combinatorial BG. Detector level study shows: smearing in the detector level decreases the discrimination power. More studies are necessary.

12. Conclusions  We apply the ME method to solve the Combinatorial BG.  We find the ME method has discriminating power.  More studies on detector smearing are necessary to apply this method.  We also hope to apply this method to BG rejection (ttbb,tt).

13. Future Plans We also start to study the ME method based on 7-body final particles. 8-body H  b b t  l  b t  j j b 7-body H t  l b t  j j b We expect this 7-body ME has more power on Combinatorial BG than the current 8-body ME.  We will report new results in the very near future.