1. Janice Drohan University College London
ttH, H->bb: Update
Janice Drohan
University College London
Overview:
Atlfast Samples
Top reconstruction: Χ2 vs Δ2
UK Atlas Higgs Meeting - RHUL - 22 April 2005

2. UK Atlas Higgs Meeting - RHUL - 22 April 2005
ttH, H->bb: Update
Generation Status:
Signal: Pythia vs Herwig (Jimmy)
Very good agreement, slightly more jets in events
Problems:
Producing large numbers of events.
Still to do:
Need to produce a ttjj (light jets only) sample
Cammin produced this by filtering at Atlfast level
Sample
Generator
# Atlfast AOD Events
Restricted decay of tops
ttH 120GeV
Pythia
300,000
Yes
Jimmy
55,000
ttjj
22M No
720,000
qq->ttbb
AcerMC
400,000
gg->ttbb
1.8M
UK Atlas Higgs Meeting - RHUL - 22 April 2005

3. UK Atlas Higgs Meeting - RHUL - 22 April 2005
Top Reconstruction
TDR Method:
Minimises: Δ2=(mlvb-mt)2+(mjjb-mt)2
Correct Jets assigned to Higgs ~25% cases
Started looking at 2nd lowest Δ2 value:
Produces correct Higgs in a similar number of cases
MH (MeV)
UK Atlas Higgs Meeting - RHUL - 22 April 2005

4. UK Atlas Higgs Meeting - RHUL - 22 April 2005
Top Reconstruction
MH (MeV)
UK Atlas Higgs Meeting - RHUL - 22 April 2005

5. UK Atlas Higgs Meeting - RHUL - 22 April 2005
Top Reconstruction
Trying to use instead of Δ2:
Using errors from within Atlfast Code for Jet energies and electron energy:
Jet: e: eta<1.4
Don’t yet have muon energy error
S. Dean writing helper function to do this.
UK Atlas Higgs Meeting - RHUL - 22 April 2005

6. UK Atlas Higgs Meeting - RHUL - 22 April 2005
Top Reconstruction
Errors looking reasonable:
Plans:
Look into performance of χ2
Assigning of b-jets to Higgs in case of 3 left
138 events out of 2155, 60 wrong combinations when choosing jets with highest pT
ANN for signal/background separation
mjjb
σmjjb
mlvb
σmlvb
mjj
σmjj
152.9
10.5
270.2
12.5
105.1
11.4
307.8
17.1
138.5
24.3
65.4
33.5
UK Atlas Higgs Meeting - RHUL - 22 April 2005