jet prob optimization for the s-channel search
DESCRIPTION
Jet Prob optimization for the s-channel search. Contents Single Top Search Jet Probability Event Selection & Jet Probability threshold Results Summary. Hideki Maehashi University of Tsukuba 7/28/2008. Single Top Search. What we want to know Intensity of weak interaction (Wtb) - PowerPoint PPT PresentationTRANSCRIPT
Jet Prob optimization for the s-channel search
Hideki MaehashiUniversity of Tsukuba
7/28/2008
Contents1.Single Top Search2.Jet Probability3.Event Selection & Jet Probability threshold4.Results5.Summary
Single Top Search
• What we want to know Intensity of weak interaction (Wtb)• There are many events which include b-jets in
final state.(Background)• Single Top s-channel cross section is too small.
• To remove many background, we use some event selections and 2 b-jet tagging.
b-jet tagging (2 way)
• Secondary Vertex• Jet Probability
Because b-quark have a life time, b do not decay at a collision point of p and anti p
p
anti p
b
t
b-jet
primary vertex
secondary vertex
SV
JP
• Jet Probability indicate likelihood of light flavor and is depended on it’s threshold.
If it’s threshold is changed, sensitivity will change.
Jet Probability Optimization
In single top group we use 5% Jet Prob Threshold, but nobody estimated which threshold makes sensitivity the best, so this time I did.
Jet Probability Threshold
Number of Jet Probability Tag
5%
which is the best sensitivity?
Jet Probability Distribution
s-channel t-channel W+bb
tt W+jets W+cc
29 kinds of threshold = 0.1% 0.3% 0.5% 1% 2% 3% 4% 5% 8% 10% 12% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
Ratio of JP, SV and at least 1SV tag
Event Selection• Exact one high PT Trigger lepton (PT > 20GeV)• Large missing Transverse Energy (ET > 25GeV)
• Two high PT jets with|η|<2.8
• Cosmic rejection, Dilepton rejection, Zboson rejection
• Choose 2 b-jet events• Likelihood Function
Discriminant (LFD >0.7)
threshold① 0.1% 0.3% 0.5% 1% 2% 3% 4% 5% 8% 10% 12%
15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
② W + jets and nonW need Mistag Rate 0.1% 0.3% 0.5% 1% 2% 3% 4% 5% 10%
Signal and BackgroundSignal : s-channel
Background : t t W+bb W+charm W+jets WW WZ Zbb Zcc Z+jets ZZ nonW
t-channel
All backgrounds are predicted by standard model.
Signals, Backgrounds and Sensitivities
Sensitivities saturate around 10% Jet Probability threshold
LFD>0.7no mistag29 threshold
Sensitivities =Signal
Background
Signals, Backgrounds and Sensitivities
LFD>0.7mistag9 threshold
Sensitivities are maximized at 10% Jet Probability threshold
Including systematic uncertainty
Sensitivities =Signal
Bstat + (ΔBsys)2
When Jet Probability’s threshold is 5% sensitivity can be max
• s-channel : 18.1%• t-channel : 18.5%• tt : 21.7%• WW : 11.2%• WZ : 10.9%• ZZ : 11.6%
• Zjet : 40.6%• Zbb : 15.3%• Zcc : 15.5%• mistag : 71.2%• nonW : 80.0%
Including systematic uncertaintyno mistag29 kinds of threshold
mistag9 kinds of threshold
Conclusion
thre Sig BKG S/B S/sqrt(B) ΔB S/sqrt(B+ΔB ) 0.1 1.50 26.8 5.62×10 0.291 6.16 0.187 0.3 2.41 42.7 5.64×10 0.368 9.93 0.202 0.5 3.00 55.2 5.44×10 0.404 12.4 0.208 1 3.99 88.2 4.53×10 0.425 19.6 0.184 2 5.20 124 4.18 ×10 0.467 25.0 0.190 3 5.99 141 4.23×10 0.503 28.0 0.197 4 6.65 160 4.15×10 0.525 30.8 0.200 5 7.12 174 4.10×10 0.540 32.9 0.201 10 8.57 238 3.60×10 0.556 43.2 0.187
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• I did Jet Prob Optimization• I found which threshold makes sensitivity the best in
29 kinds (9 kinds : mistag) of threshold and estimated with systematic uncertainty.
• 5% threshold is the best threshold to make sensitivity max.
Jet Probability Distribution• I used Monte Carlo simulation of