Cut optimisation on SU1

1
Cut optimisation on SU1

• Cuts on jets pT
• Feasibility of third lepton selection
• SM background Zjets (fast)

Lecce-Napoli phonemeeting 18/7/2006
2
Cuts on jets pT

• Run on full simulation SU1 point (22.6 fb-1).
• Presently 4 jets are required to be in the event,
  having pT gt 100, 50, 50, 50 GeV. In SU1 full this
  cuts signal with fraction 0.45 and SUSY bckg 0.38
• Two harder scenarios have been also considered

3
Feasibility of third lepton selection

• Run on full simulation SU1 point (22.6 fb-1).
• Present selection based on only 2 leptons 301
  signal events out of 2196 (S/B0.159).
• Asking for 3 (or more) leptons we gain other 68
  signal events out of 335 (S/B0.255?12), where
  ?12 is the efficiency in guessing the correct
  dilepton in selection.
• No evident criteria observed for this guessing
  (pT, mll, ETisol, ?R)
• Even if we got ?12 1 the total S/B would be
  0.171 (no appreciable increase) while our
  selection efficiency would increase by a relative
  ?20 only.

4
Z?lljets available ATLFAST samples
Files located in /castor/cern.ch/grid/atlas/dataf
iles/susy/atlfast/2006_b/ZllJetsAlpgen (same
amount of muons and electrons processed)
5
Dilepton invariant mass in Z?ll
Dielectrons ? 3 GeV
Dimuons ? 10 GeV
6
Z?ll bckg on SU1 signal
Normalized to 23 fb-1
m(ll)
7
Z?ll bckg on SU1 signal
Normalized to 23 fb-1
m(llj)
8
Missing ET SM bckg vs. SU1