single top search

Single Top search- Estimation of background rejection power with S

+J tagger using Mistag Matrix

MotivationCurrent Study and CDF NOTESignal/Background Sample

ContentsK. NakamuraUniv. of Tsukuba

Motivation

|Vtb|

|Vtb|

t-channel

s-channel

Produced electroweakly couplingDirect access to W-t-b vertex

singletop~|Vtb|2Top-polarization study and V-A structure of EW top interaction

Background study for SM Higgs searchExactly the same final state as WH->WbbBackground of all channels to use W+njet background

Probe b-quark PDF (t-channel)Non-SM phenomena

Heavy W’ bosonAnomalous W-t-b coupling ……

But…Cross section is small (~40% of tt)Larger background cause of W+2jets bin

Not established a significant evidence yet …

Current Study and CDF NOTE

Signal Acceptance and Monte Carlo based backgrounds (CDF 7863)Validation of single-top signal samples (CDF 7701)

Event selection and MC validation

Anlysis with 0.7 fb-1 (CDF 8112)Non-W and W+njets (n=1,2,3) background estimationNeural network b-tagger (CDF 7816)Kinematics fitter for top quark reconstruction (CDF 749)Construct discriminates with Neural network with Likelihood ratio

Unit : pbLimit : 95%CL

theory Likelihood Ratio

Neural Network

t-channel 1.98±0.21 < 3.1

s-channel 0.88±0.07 < 3.2

t+s comb. 2.86±0.28 < 5.8 < 3.4

Result

Phys. Rev. D 71, 012005 (2005)

Projections for Single Top Sensitivity

W+nP Background n=2,3W+2P

W+3P

Statistics of the background is small…But we confirmed ~10 times rejection power

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Last meeting result……

Signal Sample

Generator : Mad EventEvent : single top s-channel LO Top Mass : Mt=175 GeV Background

SampleGenerator : Alpgen + pythiaEvent : W(->e)+nP W(->mu)+nP (n = 0,1,2,3,4)

Mistag matrix

W(->e)+4P

Jet multiplicity distribution of b-tag performanceSecVtx JetProb

Cross checkJet multiplicity distribution after b tag (CDF 7863)

19.2% 64.7% 13.6% 2.1% 0.3%

Good agreement !?

Use Jprob<0.05 cuts for Jet Prob.

About 68 % statistics of the 2 tag events is increased to use S+J tagging We can use 30% of tight jets to combine s+s & s+j tagging >>> about half of at least 1 secvtx tag

Double tag SecVtx + SecVtx SecVtx + JetProb

W+nP Background n=2,3W+2P

W+3P

Statistics of the background is small…But we confirmed ~10 times rejection power

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Summery and PlanDouble tag included s+j tagging has potential to improve s/n ratio and significance.

statistics of the signal is increased 1.68 x s-s tag We can use 30% of tight jets to combined s-s s-j tag About 10 times rejection power is estimated with W+nP sample.

Detail of signal selection will have to be confirmed. We will apply this double-tag method to other “non-b” background like 3jets . We will estimate signal significance and discovery potential as the function of luminosity……

Because of just started , we have many “TO DO”……

Backup

CEM ele ID PHX ele ID

ID

Gen info after geometrical cuts

muonelectronlepton

L5 MET correction