Jet Prob optimization for the s-channel search Hideki Maehashi University of Tsukuba 7/28/2008 Contents 1.Single Top Search 2.Jet Probability 3.Event Selection & Jet Probability threshold 4.Results 5.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-channelt-channelW+bb ttW+jetsW+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 P T Trigger lepton (P T > 20GeV) Large missing Transverse Energy (E T > 25GeV) Two high P T jets with|η|<2.8 Cosmic rejection, Dilepton rejection, Zboson rejection Choose 2 b-jet events Likelihood Function Discriminant (LFD >0.7)

threshold ①0.1% 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% ②W + jets and nonW need Mistag Rate 0.1% 0.3% 0.5% 1% 2% 3% 4% 5% 10% Signal and Background Signal : 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>0.7 no mistag 29 threshold Sensitivities = Signal Background

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

Including systematic uncertainty Sensitivities = Signal B stat + (ΔB sys ) 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 uncertainty no mistag 29 kinds of threshold mistag 9 kinds of threshold

Conclusion thre Sig BKG S/B S/sqrt(B) ΔB S/sqrt(B+ΔB ) × × × × × × × × × 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