study of hadronic w decays in the jets + met final state

Sung-Won Lee 1

Study of Hadronic W Decays Study of Hadronic W Decays

in the Jets + MET Final Statein the Jets + MET Final StateKittikul Kovitanggoon* & Sung-

Won LeeTexas Tech University

Michael Weinberger & Teruki Kamon

Texas A&M University

Outline

1) Motivation : Why W jj?

2) Review of Data-Driven Method to detect W bosons

3) Introduce the new jet energy correction “ quark jet energy”

4) Testing with TTbar events

5) Testing with SUSY LM7 events

6) Summary

Hadronic W decays in the Jets+MET Final State 2

The analysis has done on CMSSW_3_3_5 with PAT.

Proton Collisions

Parton Collisions

Bunch Crossing

Standard Model particles (e.g. tt…)& New Particles (Higgs, SUSY, ....)

Detecting W bosons in the Jets+MET final state is a key in a SUSY scenario. We have been testing a Data-Driven method to extract hadronic W decays.

Hadronic W decays in the Jets+MET Final StateHadronic W decays in the Jets+MET Final State 3

Motivation: Why Wjj?

W j+j hadronic decays 67.60%W e+ν 10.70%W μ+ν leptonic decays 10.50%W τ+ν 11.20%

EventEvent JetsJets M(jj)M(jj) M(jj)M(jj)

1 1a, 1b, 1c

2 2a, 2b M(2a, 1a), M(2a, 1b), M(2a, 1c)M(2b, 1a), M(2b, 1b), M(2b, 1c)

M(2a, 2b)

3 3a, 3b, 3c, 3d M(3a, 2a), M(3a, 2b), M(3b, 2a), M(3b, 2b), M(3c, 2a), M(3c, 2b), M(3d, 2a), M(3d, 2b)

M(3a, 3b), M(3a, 3c), M(3a, 3d),M(3b, 3c), M(3b, 3d), M(3c, 3d)

4 For each jjii in Event XX, MM((jji i jjkk) ) is calculated with jjkk in Event XX11

Data Driven MethodForming M(jj) Distributions

Same Event: any pairs of jets of the current event

Mixed Event: any pairs of jets of the current + previous events

[Step.1] [Step.2]


Previous studies


• The last talk on this analysis can be found at http://indico.cern.ch/conferenceDisplay.py?confId=81844• We moved from CMSSW_2_2_9 to CMSSW_3_3_5. The main different from both versions is the jet algorithms i.e. IC5 and Antikt 5. The study showed that there is no much difference between both algorithms.• Two b-tag algorithms, track counting high efficiency and track counting high purity, were studied. The result showed that track counting high efficiency give us better efficiency.• Also, on ttbar sample double b tags was applied. We get the better shape of W mass but loss a lot of statistic.

• Due to the over-calibration of the L2L3 energy correction which is the default in PAT the new energy correction is required for reconstructing W mass • Based on CMS AN-2010/004 by Alexandre Nikitenko, Efe Yazgan http://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=6&confId=81091 • This method is optimized to quark-rich sample• Correction factors are eta and pTdependent of jets up to eta < 3.2 and are applied to raw jet pT • Data Set /TTbar/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO


Jets selection 1.Required that jets pT > 30 GeV with corresponding correction2.MC matching to selecting the jets from W

M(jj) (GeV/c2)

En

trie

s

TOP Production

)( )( bWbWttpp jj l

Event Selection - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV

Event Selection - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV

M(jj) Reconstruction - Jet pT > 30 GeV/c - Jet < 3 - HighEfficenecy b tag < 2.03 - ΔR(jj) > 0.5

M(jj) Reconstruction - Jet pT > 30 GeV/c - Jet < 3 - HighEfficenecy b tag < 2.03 - ΔR(jj) > 0.5

Data Set /TTbar/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO


Same Events Mixed Events


Same event

Log Scale

300-500 GeV/c2

Normalization Region

M(jj) (GeV/c2)

M(jj) (GeV/c2)

M(jj) (GeV/c2)

M(jj) (GeV/c2)

En

trie

s

En

trie

s

En

trie

s

En

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s


• On the slide the important of b-tag will be discussed • The analysis was repeated by using L2L3+L5 and quark-jet energy correction

Peak position

MW

M(jj) (GeV/c2)

En

trie

s

• According to the previous gen-level analysis, the shoulder is due to the b-jets contamination• In order to remove this , b-tag algorithm is needed • The b-tag algorithm is “Track counting high efficiency” with discriminator < 2.03http://indico.cern.ch/getFile.py/access?contribId=8&resId=0&materialId=slides&confId=50255


1. b-tag is needed to eliminate b-jet contamination2. Based on previous study, “track counting high efficiency” discriminator < 2.03 is the best for

eliminate b jet contamination

Without b-tag

With b-tag

With double b-tags

M(jj) (GeV/c2)

En

trie

s


Conclusions1.The quark-jet energy correction give us better peak position of W mass. However, we lost some jets due to the lower energy after the correction.2.Although we still see a large backgrounds even after the subtraction we will be able to see the W mass.

L2L3

L2L3 + L5

Quark jet energy correction

MW M(jj) (GeV/c2)

En

trie

s

))()(( 01

02 ~bWbW~ttg~

Event Pre-Selection• ET

miss > 180 GeV;

• N(J) > 2 with ET J1,J2 > 200 GeV;

• ETmiss + ET

J1 + ETJ2 > 600 GeV

N(jjii) > 2 with pT > 30 GeV jets < 3ΔR(jj) > 0.5

W

W -b0

2~

01~

tt

• J : represented the 1st and 2nd leading jets• j : represented the other jets that are not the 1st and 2nd leading jets

Data Set: /LM7/Summer09-MC_31X_V3_7TeV_AODSIM-v1/AODSIM


M(jj) in Data-Driven Method with L2L3

Same Events Mixed Events

Same event

Log Scale

300-500 GeV/c2

Normalization Region

Hadronic W decays in the Jets+MET Final State 13M(jj) (GeV/c2)

M(jj) (GeV/c2)

M(jj) (GeV/c2)

M(jj) (GeV/c2)

En

trie

s

En

trie

s

En

trie

s

En

trie

s

Wjj with L2L3

Hadronic W decays in the Jets+MET Final State

Peak position

• The analysis was repeated by using L2L3+L5 and quark jet-energy correction

14

MW

M(jj) (GeV/c2)

En

trie

s

Wjj with L2L3, L2L3+L5, QJE Correction


MW

L2L3

L2L3 + L5

Quark jet energy correction

Conclusions1.The quark jet-energy correction give us better peak position of W mass.2.Although we still see a large backgrounds even after the subtraction (larger than ttbar case) we will be able to see the W mass.3.The study of the new event selections is required to eliminate more background

M(jj) (GeV/c2)

En

trie

s

Summary


1) The data-driven method seem to work on extracting hadronic W decay in TTbar and LM7 events.

2) The b-tag algorithm is necessary for eliminate the b jet contamination.

3) The quark jet energy correction solves the overcorrected jet energy. This correction give us the better W mass peak at around 80 GeV.

4) More systematic study will be planned: • Mixing signal with background Z+jets, W+jets, etc• Optimizing the event section for SUSY LM7

Back up

Quark-Jet Calibration using Z+Jet Events

measure

cq/cq=ratio of the quarkAnd gluon jet calib. Coefficients from MC(ET

j and jdependent)

cq/cq=ratio of the quarkAnd gluon jet calib. Coefficients from MC(ET

j and jdependent)

Ratio of Z+q (Z+g)Cross section to theTotal cross section.(function of PT

Z and j)

Ratio of Z+q (Z+g)Cross section to theTotal cross section.(function of PT

Z and j)

(Z+g)/TOT(Z+g)/TOT(Z+q)/TOT(Z+q)/TOT

Alexandre Nikitenko,Efe YazganAlexandre Nikitenko,Efe Yazgan

CMS AN-2010/004CMS AN-2010/004

http://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=6&confId=81091 http://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=6&confId=81091

The calibration coefficients for the quark jets, cq, can be obtained from:The calibration coefficients for the quark jets, cq, can be obtained from:

18

Determining Correction Coefficients

• Determine each parameter for each j, PT

Z interval (using 2D maps), and then find the quark coefficients, cq. 0.4

PT=20 GeV0.4PT=20 GeV

Alexandre Nikitenko,Efe YazganAlexandre Nikitenko,Efe Yazgan

19

study of hadronic w decays in the jets + met final state

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