sung-won lee 1 study of hadronic w decays in the jets + met final state study of hadronic w decays...

Sung-Won Lee 1

Study of Hadronic W Decays Study of Hadronic W Decays

in the Jets + MET Final Statein the Jets + MET Final State

Kittikul KovitanggoonDepartment of PhysicsTexas Tech University

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 SM and SUSY scenario. But, a huge combinatorial background in multi-jet final state is a serious problem. We introduce 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 2

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%

Outline

Hadronic W decays in the Jets+MET Final State 3

Extraction Hadronic W

Jet Energy Correction

Calo Collection

Data-Driven Method

Generator Level and B-TaggerAnalysis Techniques

pp Colision at 7 TeVFor Luminosity 110 nb-1

η swapping Data-Driven Method

PF Collection

Monte Carlo Data pp Colision Data

SUSY LM7tt

tt

Analysis Software


• The analysis is based on CMSSW.

• The Physics Analysis Toolkit (PAT) is a high-level analysis layer in the framework of the CMSSW.

• Jet energy corrections: - L2(η dependent)+L3(pT dependent) is currently the default correction in CMS. - L2L3+L5(jet Flavor dependent) which uses light quarks i.e. up, down, and strange quarks. - Quark-jet energy correction.

• Jet Collections:

Data-Driven MethodForming M(jj) Distributions


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)

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

for normalizationfor normalization

M(jj)M(jj)Mcut

Same Event: any pairs of jets of the current event

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

• Due to the over-calibration of the L2L3 energy correction 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 η and pT dependent of jets up to η < 3.2 and are applied to raw jet pT .


Jets Selections 1.Required that jets pT > 30 GeV with corresponding correction.2.MC matching to selecting the W jets.

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


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Data Set: Data Set: WWMW MW

• The QJE give us the best calibration for reconstructing hadronic W boson

tt

TOP Production with Calorimeter Jets )( )( 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 - ΔR(jj) > 0.5

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

Data Set Summer08 with CMSSW_2_2_9 and corresponding PAT


Using 300 to 500 GeV as normalization range

tt


Expected shoulder due to b-jets contamination

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Peak position

• Without b-tagger and proper energy correction, the over calibrated mass and shoulder are presented.

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Generator Level Study for

Hadronic W decays in the Jets+MET Final State at the LHC 10

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s• In order to confirm the effect of b jet contamination, the generator level jets were used in data-driven method.

• The result shows that the shoulder is due to the b jets contamination.

b-tagger Analysis

Hadronic W decays in the Jets+MET Final State at the LHC

• In order to remove this shoulder, b-tag algorithm is needed.• The two "Track Counting" algorithms based on impact parameter i.e. “High efficiency”” and “High Purity” were recommended to use.• The track counting approach identifies a jet as b by calculating the signed impact parameter significance (S) of all good tracks, and orders them by decreasing significance. Its b tag discriminator is defined as the significance (S) of the N'th track. • S of N = 2 is high efficiency and N = 3 for high purity.• The higher the discriminator value, the more likely the jet is b jet. • The cut number is recommended by b-tagging analysis group:

11

• We chose the loose cuts for b-taggers because it can pick the most b jets.

b-tagger Analysis


•This study was done on CMSSW_3_3_5 with PAT on summer09 sample.tt

The plot show the dijet mass after the subtraction with high

efficiency < 2.03.

The Parton flavor of jets with and without b-tagger.

• The b-tagger eliminates the shoulder from our dijet mass.

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b-tagger Analysis


• Two track counting algorithms is studied.• High efficiency gives us the better shape than high purity in the same loose point.

• We also study how changing b discriminator values affect the mass shape. • Decreasing the value should give us the better mass shape?• Decreased the value worst mass shape.• Increased the value same mass shape.

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M(jj) (GeV/c2)M(jj) (GeV/c2)

b-tagger Analysis


• To understand how the changing discriminator values effect the shape of dijet mass.• Investigating the b discriminator values of the W jets and b jets with MC matching.

• Decreased the discriminator value lose W more than b. • Increased the discriminator value gain W as many as b.• Impossible to lose b while gain W.• We decided to use the high efficiency discriminator value of 2.03

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TOP Production with Calorimeter Jets

)( )( bWbWttpp jj l

Event Selections - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV - At least 1 b jet (discriminator >2.03)

Event Selections - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV - At least 1 b jet (discriminator >2.03)

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


Data Set TTbar Sping10 with CMSSW_3_5_7 and corresponding PAT




Same Events Mixed Events

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Result of Calorimeter Jets


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Normalization Region

300-500 GeV/c2




Peak position

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• As we expect, the b-tagger help us to eliminate the b jet contmination.• The mass peak at around 95 GeV is over calibrated by L2L3 JEC

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Peak position

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Peak position

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Result of Calorimeter JetsE

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• The data-driven method seem to work. • The high efficiency b-tagger and JEC are important to this analysis.

TOP Production with Particle Flow Jets )( )( bWbWttpp

jj l

Event Selections - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV - At least 3 PF jets with L2L3 pT > 25 GeV - At least 1 jet with L2L3 pT > 25 GeV is b jet

Event Selections - Electron pT > 20 GeV/c - Electron Isolation < 0.1 - Standard Electron Identification - Electron < 2.5 - Missing Transverse Energy > 20 GeV - At least 3 PF jets with L2L3 pT > 25 GeV - At least 1 jet with L2L3 pT > 25 GeV is b jet



Data Set TTbar Sping10 with CMSSW_3_5_7 and corresponding PAT




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Result of PF Jets

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• With track information, the over calibrated jet energy is not an issue.• Combined with high efficiency b-tagger, the clear peak at 80 GeV of W mass is evident.


• Supersymmetry (SUSY) provides an elegant solution for a cold dark matter candidate. The minimal SUGRA framework indicate that gluinos is lightest. The gluinos decay to pairs of tops plus the lightest supersymmetric particle (LSP).

Point m0

Gevm1/2

Gevtanβ Sgn

μA0

LM0 200 160 10 + -400

LM1 60 250 10 + 0

LM2 185 350 35 + 0

LM3 330 240 20 + 0

LM4 210 285 10 + 0

LM5 230 360 10 + 0

LM6 85 400 10 + 0

LM7 3000 230 10 + 0

LM8 500 300 10 + -300

LM9 1450 175 10 + 0

mSUGRA is characterized by five free parameters:• m0 the common mass of scalar particle at GUT scale

• m1/2 the common fermion mass

• A0 the common trilinear coupling• μ the sign of the higgsion mass parameter• tanβ the ratio between the expectation values of 2 Higgs doublets

))()(( 01

02 ~bWbW~ttg~

Event Pre-Selection• MET > 180 GeV; • N(J) > 2 with ET J1,J2 > 200 GeV;

• MET + ETJ1 + ET

J2 > 600 GeV

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

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

Data Set SUSY LM7 Spring10 with CMSSW_3_5_7 and corresponding PAT




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• This results show that data-driven method seem to work on SUSY signal.• However, this analysis is still in the early state. More detail studies are required.

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Time for the real data from CMS LHC


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An interesting physics? Yes, W jj. Large QCD cross section. ∆φ(jj) ~ 180 deg. Special treatment in mix event. Choose two leading jets in each event. Swap the η’s, not φ’s, to maintain “QCD dijet”

structure.

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Data set are:- /MinimumBias/Commissioning10-SD_JetMETTau-Jun14thSkim_v1/RECO- /JetMETTau/Run2010A-Jun14thReReco_v2/RECO -/JetMETTau/Run2010A-PromptReco-v4/RECO

Corresponding JSON files: - Cert_135059-135735_7TeV_June14thReReco_Collisions10_JSON.txt- Cert_136066-137028_7TeV_June14thReReco_Collisions10_JSON.txt- Cert_138564-140076_7TeV_StreamExpress_Collisions10_JSON.txt

The data set is corresponding to an integrated luminosity of 110 nb-1

This analysis is done on CMSSW_3_7_0_patch2 with corresponding PAT.


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Event Selections - ak5 calo jets - Trigger 0 AND NOT (36 OR 37 OR 38 OR 39) - Scraping veto - Good Primary vertex - HLT bits: HLT_Jet15U - JEC: L2+L3 “spring10” - |ηjet1| < 1.3 && |ηjet2| < 1.3 - 2 leading jets passing the loose jet id - Jet pT > 30 GeV - Jets back to back i.e. ||Δφ| - π|<0.2

Using 200 to 500 GeV as normalization range and using the variable bin size to gain more statistic in the high mass region.

• The first result showed the negative entries due to the high number of QCD jets compared to W jets.• Moreover, the low entries in the region of normalization in mix event.• New techniques are required.


s• We studied the behavior of between W jets and QCD dijets• Studying is done on spring10 data by matching hadronic W and on QCD4Jets spring10 data.

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• of QCD jets is broader range than that of W jets.• The signal (W) over background (QCD) shows us that the optimized point is around = 0.8.• Imposeing the requirement of jet pT ratio between the second jet in the same event and the jet in the mix event greater than 0.8 to increase the mix event at high mass region.


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Event Selections - ak5 calo jets - Trigger 0 AND NOT (36 OR 37 OR 38 OR 39) - Scraping veto - Good Primary vertex - HLT bits: HLT_Jet15U - JEC: L2+L3 “spring10” - | ηjet1 | < 1.3 && | ηjet2| < 1.3 - 2 leading jets passing the loose jet id - Jet pT > 30 GeV - Jets back to back i.e. ||Δφ| - π|<0.2 - |Δη| < 0.8 - Pt ratio between second jet in same event and jet in mix event > 0.8

Using 200 to 500 GeV as normalization range and using the variable bin size to gain more statistic in the high mass region.


Same Events Mixed Events

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Log Scale

Normalization Region

200-500 GeV/c2




Peak position

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• New techniques can eliminate negative mass and give us the better mass window.• The peak position lower than W mass because many QCD jets passed our event selections.• This method is still pre-mature. We need more detailed studies.

Summary and Plans


• Extracting the hadronic W decay is important for both Standard Model and SUSY events.• The studies show that the data-driven method seems to work on extracting hadronic W.• Proper b-tagging could help us to see clearly mass peak with less combinatorial background.• Various jet energy corrections and PF jets can solve the over-calibrating energy.

The future plans are:1.Mixing the signal with the backgrounds. 2. More detail studies of η swapping data-driven method.3. Optimizing new event selections for SUSY LM7. 4. Test on SUSY LM0.

sung-won lee 1 study of hadronic w decays in the jets + met final state study of hadronic w decays...

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