Cut optimisation on SU1

•Cuts on jets’ pT

• Feasibility of third lepton selection

• SM background: Z+jets (fast)

Lecce-Napoli phonemeeting – 18/7/2006

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 > 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:

pT1,2,3,4 cuts SU1 signal

SU1 bckg

ttbar lnln+2jets

100,50,50,50 GeV 45.1% 38.3% x

150,100,50,50 GeV 43.2% 35.6% 0.6x

150,100,80,50 GeV 39.0% 30.7% 0.45x

Feasibility of third lepton selection

• Run on full simulation SU1 point (22.6 fb-1).• Present selection based on onlyonly 2 leptons: 301

signal events out of 2196 (S/B=0.159).• Asking for 3 (or more) leptons we gain other 68

signal events out of 335 (S/B=0.255*12), where 12 is the efficiency in “guessing” the correct dilepton in selection.

• No evident criteria observed for this guessing (pT, mll, ET

isol, R…)• Even if we got 12 =1 the total S/BS/B would be 0.171

(no appreciable increase) while our selection efficiency would increase by a relative 20% only.

Zll+jets available ATLFAST samples

SamplesCross

sectionGenerated statistics

Filtered analyzed events

Z+1jet 179.8 pb 11.1 fb-1 75k

Z+2jets 56.4 pb 49.8 fb-1 158k

Z+3jets 14.1 pb 99.3 fb-1 195k

Z+4jets 3.3 pb 99.5 fb-1 97k

Z+5jets 0.7 pb 50.1 fb-1 18k

Files located in:/castor/cern.ch/grid/atlas/datafiles/susy/atlfast/2006_b/ZllJetsAlpgen(same amount of muons and electrons processed)

Dilepton invariant mass in Zll

Dielectrons ~ 3 GeV

Dimuons ~ 10 GeV

Zll bckg on SU1 signalNormalized to 23 fb-1

m(ll)

Normalized to 23 fb-1

Zll bckg on SU1 signal

m(llj)

Missing ET: SM bckg vs. SU1