Jet Prob optimization for the s-channel search

1. 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

2. 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.

3. b-jet tagging (2 way) Because b-quark have a life time, b do not decay at a collision point of p and anti p • Secondary Vertex • Jet Probability secondary vertex b-jet primary vertex b SV p anti p t JP

4. Jet Probability Optimization • Jet Probability indicate likelihood of light flavor and is depended on it’s threshold. If it’s threshold is changed, sensitivity will change. Number of Jet ProbabilityTag which is the best sensitivity? In single top group we use 5% Jet Prob Threshold, but nobody estimated which threshold makes sensitivity the best, so this time I did. 5% Jet Probability Threshold

5. Jet Probability Distribution s-channel t-channel W+bb tt W+jets W+cc

6. 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

7. 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)

8. 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% • W + jets and nonW need Mistag Rate 0.1% 0.3% 0.5% 1% 2% 3% 4% 5% 10% Signal and Background Signal : s-channel t-channel Background : t t W+bb W+charm W+jets WW WZ Zbb Zcc Z+jets ZZ nonW All backgrounds are predicted by standard model.

9. Signals, Backgrounds and Sensitivities LFD>0.7 no mistag 29 threshold Signal Sensitivities = Background Sensitivities saturate around 10% Jet Probability threshold

10. Signals, Backgrounds and Sensitivities LFD>0.7 mistag 9 threshold Sensitivities are maximized at 10% Jet Probability threshold

11. Including systematic uncertainty • Zjet : 40.6% • Zbb : 15.3% • Zcc : 15.5% • mistag : 71.2% • nonW : 80.0% • s-channel : 18.1% • t-channel : 18.5% • tt : 21.7% • WW : 11.2% • WZ : 10.9% • ZZ : 11.6% Signal Sensitivities = When Jet Probability’s threshold is 5% sensitivity can be max 2 Bstat + (ΔBsys)

12. Including systematic uncertainty no mistag 29 kinds of threshold mistag 9 kinds of threshold

13. Conclusion • 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. 2 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 2 2 2 2 2 2 2 2 2

14. Jet Probability Distribution • I used Monte Carlo simulation of