Study of
Download
1 / 36

Study of Hadronic W Decays in the Jets + MET Final State - PowerPoint PPT Presentation


  • 81 Views
  • Uploaded on

Study of Hadronic W Decays in the Jets + MET Final State. Kittikul Kovitanggoon Department of Physics Texas Tech University. Motivation: Why W jj ?. Bunch Crossing. Proton Collisions. Parton Collisions. W  j + j hadronic decays 67.60%

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Study of Hadronic W Decays in the Jets + MET Final State' - maddy


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Study of Hadronic W Decays in the Jets + MET Final State

Kittikul Kovitanggoon

Department of Physics

Texas Tech University


Motivation why w jj
Motivation: Why Wjj?

Bunch Crossing

Proton Collisions

Parton Collisions

W j+jhadronic decays 67.60%

W e+ν 10.70%

W μ+νleptonic decays 10.50%

W τ+ν 11.20%

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 State

2


Outline

Extraction Hadronic W

Monte Carlo Data

pp Colision Data

η swapping Data-

Driven Method

Jet Energy Correction

Generator Level and B-Tagger

Analysis Techniques

Data-Driven Method

pp Colision at 7 TeV

For Luminosity 110 nb-1

Calo Collection

SUSY LM7

PF Collection

3

Hadronic W decays in the Jets+MET Final State


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:

4

Hadronic W decays in the Jets+MET Final State


Data driven method

Forming M(jj) Distributions

Data-Driven Method

  • Same Event: any pairs of jets of the current event

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

for normalization

Mcut

M(jj)

5

Hadronic W decays in the Jets+MET Final State


Review of Quark Jet Energy (QJE) Correction

  • 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 ηand pTdependent of jets up to η < 3.2 and are applied to raw jet pT .

  • Jets Selections

  • Required that jets pT> 30 GeV with corresponding correction.

  • MC matching to selecting the W jets.

6

Hadronic W decays in the Jets+MET Final State


Review of Jet Energy Corrections

Entries

Entries

MW

MW

Data Set:

Data Set: WW

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

7

Hadronic W decays in the Jets+MET Final State


TOP Production with Calorimeter Jets

Data Set Summer08 with CMSSW_2_2_9 and corresponding PAT

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

Using 300 to 500 GeV as normalization range

8

Hadronic W decays in the Jets+MET Final State


First Result of TOP Pair Production of Data-Driven Method

Expected shoulder due to b-jets contamination

Entries

Peak position

MW

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

9

Hadronic W decays in the Jets+MET Final State


Generator level study for
Generator Level Study for

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

Entries

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

10

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


B tagger a nalysis
b-tagger Analysis

  • 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:

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

11

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


B tagger a nalysis1
b-tagger Analysis

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

Entries

Entries

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.

12

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


B tagger a nalysis2
b-tagger Analysis

  • Two track counting algorithms is studied.

  • High efficiency gives us the better shape than high purity in the same loose point.

Entries

Entries

M(jj) (GeV/c2)

M(jj) (GeV/c2)

  • 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.

13

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


B tagger a nalysis3
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.

Entries

  • 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

14

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


TOP Production with Calorimeter Jets

Data Set TTbarSping10 with CMSSW_3_5_7 and corresponding PAT

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

Using 300 to 500 GeV as normalization range

15

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

Same Events

Mixed Events

16

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

300-500 GeV/c2

Log Scale

Normalization Region

17

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

Peak position

MW

  • 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

18

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3 + L5 and QJE

Result of Calorimeter Jets

Peak position

Peak position

Entries

Entries

MW

MW

19

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with all JECs

Result of Calorimeter Jets

Entries

MW

  • The data-driven method seem to work.

  • The high efficiency b-tagger and JEC are important to this analysis.

20

Hadronic W decays in the Jets+MET Final State


TOP Production with Particle Flow Jets

Data Set TTbarSping10 with CMSSW_3_5_7 and corresponding PAT

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 L2L3pT> 25 GeV is b jet

M(jj) Reconstruction

- Jet pT > 25 GeV/c

- Jet discriminator < 2.03

- Jet < 3

- ΔR(jj) > 0.5

Using 300 to 500 GeV as normalization range

21

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of PF Jets

Entries

Entries

MW

  • 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.

22

Hadronic W decays in the Jets+MET Final State


Super Symmetry Low Mass Point 7 (SUSY LM7)

  • 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).

  • mSUGRA is characterized by five free parameters:

  • m0the common mass of scalar particle at GUT scale

  • m1/2 the common fermion mass

  • A0the common trilinear coupling

  • μthe sign of the higgsion mass parameter

  • tanβthe ratio between the expectation values of 2 Higgs doublets

23

Hadronic W decays in the Jets+MET Final State


SUSY LM7 production @ LHC

Event Pre-Selection

  • MET > 180 GeV;

  • N(J) > 2 with ETJ1,J2 > 200 GeV;

  • MET + ETJ1 + ETJ2 > 600 GeV

N(ji) > 2 with pT > 30 GeV

jets < 3

ΔR(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

Using 300 to 500 GeV as normalization range

Data Set SUSY LM7 Spring10 with CMSSW_3_5_7 and corresponding PAT

24

Hadronic W decays in the Jets+MET Final State


First Result of SUSY LM7 Production of Data-Driven Method

Result of Calorimeter Jets

Entries

Entries

MW

MW

  • 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.

25

Hadronic W decays in the Jets+MET Final State


Early LHC Data at = 7 TeV

Time for the real data from CMS LHC

26

Hadronic W decays in the Jets+MET Final State


η Swapping Data-Driven Method

  • An interesting physics? Yes, Wjj.

  • 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.

#1

2

2

#2

Event #n

Event #n+1

1

1

#3

3

2

3

2

#4

1

27

Hadronic W decays in the Jets+MET Final State


Test on Early LHC Data at = 7 TeV

  • 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.

28

Hadronic W decays in the Jets+MET Final State


Test on Early LHC Data at = 7 TeV

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.

29

Hadronic W decays in the Jets+MET Final State


Techniques for Analyzing Early LHC Data at = 7 TeV

  • 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.

Entries

  • of QCD jets is broader range thanthat 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.

30

Hadronic W decays in the Jets+MET Final State


Test on Early LHC Data at = 7 TeV

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.

31

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

Same Events

Mixed Events

32

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

200-500 GeV/c2

Normalization Region

Log Scale

33

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

Entries

Peak position

MW

34

Hadronic W decays in the Jets+MET Final State


M(jj) in Data-Driven Method with L2L3

Result of Calorimeter Jets

Entries

  • 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.

35

Hadronic W decays in the Jets+MET Final State


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:

Mixing the signal with the backgrounds.

More detail studies of η swapping data-driven method.

3. Optimizing new event selections for SUSY LM7.

4. Test on SUSY LM0.

36

Hadronic W decays in the Jets+MET Final State


ad