mc validation: comparison alpgen vs. mc@nlo

MC validation: comparison MC validation: comparison ALPGEN vs. MC@NLOALPGEN vs. MC@NLO

Osamu Jinnouchi (KEK)Osamu Jinnouchi (KEK)S. Asai (Tokyo)S. Asai (Tokyo)

Special thanks toSpecial thanks to Michelangelo Mangano (CERN) Michelangelo Mangano (CERN)

Oct. 20, 2005 LCG MC Validation meetingOct. 20, 2005 LCG MC Validation meeting

Activity in ATLASActivity in ATLAS

Oct. 20 2005 O.Jinnouchi (LCG MC validation) 2

prefacepreface

ه This study This study is notis not based on the atlas detector simulation, based on the atlas detector simulation, but based on the MC truth information so but based on the MC truth information so this is not this is not ATLAS specificATLAS specific (I believe this fits better to the purpose of (I believe this fits better to the purpose of this meeting)this meeting)

ه This work is from one of the recent activities in SUSY WG This work is from one of the recent activities in SUSY WG in ATLAS about experience in ALPGEN and MC@NLO in ATLAS about experience in ALPGEN and MC@NLO (this talk is (this talk is not the reviewnot the review of all the activities in ATLAS) of all the activities in ATLAS)


OutlineOutline

ه IntroductionIntroductionه ME and PSME and PS

ه MC samples MC samples ه ALPGEN, MC@NLO in ATLAS Athena frameworkALPGEN, MC@NLO in ATLAS Athena framework

ه Comparison using top-pair samplesComparison using top-pair samplesه TopTop

ه JetsJets

ه Available samples for the productionAvailable samples for the production


ME (matrix element) and PS (parton shower)ME (matrix element) and PS (parton shower)

Two major MC codes (ALPGEN, MC@NLO) are comparedTwo major MC codes (ALPGEN, MC@NLO) are comparedه ALPGENALPGEN

ه Leading order calculations for ME Leading order calculations for ME ه ME used for all jets ME used for all jets ه Exclusive Exclusive the contributions (N=0, 1, 2, …) have to the contributions (N=0, 1, 2, …) have to be summed later (see cartoon in next slide)be summed later (see cartoon in next slide)

ه MC@NLOMC@NLOه Order Order s s calculation for ME (1calculation for ME (1stst jet is well described) jet is well described)ه Parton Shower for additional jetsParton Shower for additional jetsه Inclusive Inclusive no user operation needed no user operation needed

Parton shower modelParton shower model can describe well about the jets in collinear region can describe well about the jets in collinear regionHowever it has a problem with jets in high Pt rangeHowever it has a problem with jets in high Pt range

In the SUSY background study, we have to deal with high-pt / high In the SUSY background study, we have to deal with high-pt / high multiplicity jets multiplicity jets ME approach is importantME approach is important


Alpgen approach in practiceAlpgen approach in practiceIf you want inclusive 3-jets samples in ALPGENIf you want inclusive 3-jets samples in ALPGEN

un-weighted event files (4-vector files) 0-jet 1-jet 2-jets 3-jets

Pyhia / Herwig(PS matching some fraction of events are vetoed)

3-jets inclusive sample

0-jetexclusive

1-jetexclusive

2-jetexclusive

exclusive exclusive exclusive inclusive

PS jets : 4+5+6+…PS jets : 4+5+6+…

By definition, MC@NLO is equivalent to By definition, MC@NLO is equivalent to 1-jet inclusive sample1-jet inclusive sample

higher order inclusive sample is better higher order inclusive sample is better but, it gets more time consuming to generate 4-vectorbut, it gets more time consuming to generate 4-vector

3-jet inclusive


MC samples( MC samples( tt tt + Njets SM background)+ Njets SM background)

ه ALPGENALPGENه Event generation – Alpgen ver 2.05Event generation – Alpgen ver 2.05

ه Hadronization – Pythia 6.323 (on Athena Rel.10.5.0) Hadronization – Pythia 6.323 (on Athena Rel.10.5.0)

- upveto correctly works with this combination- upveto correctly works with this combination

- user defined matching condition- user defined matching condition

ه MC@NLOMC@NLOه Event generation – MC@NLO ver 3.1Event generation – MC@NLO ver 3.1

ه Hadronization – Jimmy4.0 (Herwig 6.5) (on Athena 10.0.4)Hadronization – Jimmy4.0 (Herwig 6.5) (on Athena 10.0.4)

about 100k events for both are used in this study about 100k events for both are used in this study QQ22

renren=Q=Q22facfac= m= m22(top)+<P(top)+<PTT(top)(top)22> (default definition in MC@NLO)> (default definition in MC@NLO)

Top is a major background in the SUSY searchTop is a major background in the SUSY search

The samples are made within ATLAS Athena frameworkThe samples are made within ATLAS Athena framework


parton-jet matching in Alpgenparton-jet matching in Alpgenه Event generation (ALPGEN) performed with light jets Pt>20GeVEvent generation (ALPGEN) performed with light jets Pt>20GeVه Additional PS jets (Pythia) must have lower Pt than ME jetsAdditional PS jets (Pythia) must have lower Pt than ME jets (reference (reference http://mlm.home.cern.ch/mlm/alpgen/http://mlm.home.cern.ch/mlm/alpgen/ ) )Some fraction of events vetoed in Pythia (matching at Pt>20GeV Rcone=0.7 )Some fraction of events vetoed in Pythia (matching at Pt>20GeV Rcone=0.7 )

Exclusive (pb)Exclusive (pb) Inclusive (pb)Inclusive (pb)

JETSJETS AFTERAFTER BEFOREBEFORE RATIORATIO AFTERAFTER BEFOREBEFORE RATIORATIO

N=0N=0 242.1242.1 486.5486.5 49.8%49.8%

N=1N=1 179.3179.3 488.8488.8 36.7%36.7% 414.2414.2 488.8488.8 84.7%84.7%

N=2N=2 78.078.0 295.1295.1 26.4%26.4%

N=3N=3 26.726.7 132.4132.4 20.2%20.2% 80.880.8 132.4132.4 61.0%61.0%

ALPGEN Sample1: N = 0 + 1ALPGEN Sample1: N = 0 + 1incinc 656.3pb 656.3pb

ALPGEN Sample2: N = 0 + 1 + 2 + 3ALPGEN Sample2: N = 0 + 1 + 2 + 3 incinc 580.2pb 580.2pb

Total Cross section is different from MC@NLO output log (Total Cross section is different from MC@NLO output log (773.4pb773.4pb) by factor 1.2~1.3) by factor 1.2~1.3


Comparison on MC Truth topComparison on MC Truth topه No kinetic cut applied on top production No kinetic cut applied on top production

at event generation at event generation good clue to good clue to check the matching performancecheck the matching performance

ه ALPGEN has high Pt tail which needs to ALPGEN has high Pt tail which needs to be understood be understood

ه Discrepancy in low Pt region is observed, Discrepancy in low Pt region is observed, it may be come from the difference btw it may be come from the difference btw Pythia/Herwig parton shower scalePythia/Herwig parton shower scale

(( additional info in next slide) additional info in next slide)

|y|<1

Scale factor 1.28 for ALPGEN

LogLog1010 Pt (GeV) Pt (GeV)

dots ALPGEN (N=0,1) + Pythia_idots ALPGEN (N=0,1) + Pythia_iline MC@NLO + Jimmy_iline MC@NLO + Jimmy_i

100GeV10GeV

(GeV)

(reason is in next slide)


ه The same plot created by M. ManganoThe same plot created by M. Mangano

ه He uses He uses ه MC@NLO + HerwigMC@NLO + Herwig

ه ALPGEN + HerwigALPGEN + Herwig

ه So the parton shower contributions are So the parton shower contributions are exactly the same (better agreement in exactly the same (better agreement in low Pt region)low Pt region)

ه High Pt tail is still observedHigh Pt tail is still observed

Comparison on top (Cont.)Comparison on top (Cont.)

|y|<1

Scale factor 1.28

We should try ALPGEN + Jimmy_i (Herwig_i) combinationCareful study is necessary

Thanks toThanks to

Michelangelo ManganoMichelangelo Mangano

Technical problem in Herwig_i is fixed in Herwig_i-00-01-80Now we can try direct comparison of Pythia_i vs. Herwig_i


Comparison between leading jetsComparison between leading jets

ه Pt distributions (of three) look almost identical Pt distributions (of three) look almost identical ه ALPGEN has more central in ALPGEN has more central in

Compare the TruthJets (cone0.7) for three data setsCompare the TruthJets (cone0.7) for three data sets - Jets not originated from top are selected - Jets not originated from top are selected - Histograms are normalized (by total cross sections for each)- Histograms are normalized (by total cross sections for each) - MC@NLO and ALPGEN (N=0+1) are supposed to be equivalent- MC@NLO and ALPGEN (N=0+1) are supposed to be equivalent - Concentrate on cone7 truth jet, lnu+qq- Concentrate on cone7 truth jet, lnu+qq

Pt (GeV)Pt (GeV)


ه The second leading jet is PS for MC@NLO, and ALPGEN (N=0,1)The second leading jet is PS for MC@NLO, and ALPGEN (N=0,1)

ه For ALPGEN (N=0-3) it is still generated from MEFor ALPGEN (N=0-3) it is still generated from ME

ه ALPGEN (N=0-3) has harder in Pt > 200GeVALPGEN (N=0-3) has harder in Pt > 200GeV

ه distributions are getting widerdistributions are getting wider

The second leading jetsThe second leading jets

Pt (GeV)Pt (GeV)


The third leading jetThe third leading jet

ه Cross section for the 3Cross section for the 3rdrd jet is somewhat lower in MC@NLO jet is somewhat lower in MC@NLOه Difference in Difference in distribution needs to be understood distribution needs to be understoodه Could be difference in Pythia/HerwigCould be difference in Pythia/Herwig

ه MC@NLO and ALPGEN (N=0,1) have similar Pt distributions (slope)MC@NLO and ALPGEN (N=0,1) have similar Pt distributions (slope)ه ALPGEN (N=0-3) has harder jetsALPGEN (N=0-3) has harder jets

Pt (GeV)Pt (GeV)

- Behavior of 1-hard jet configuration compared (MC@NLO vs. ALPGEN(N=0,1))- Behavior of 1-hard jet configuration compared (MC@NLO vs. ALPGEN(N=0,1))- The difference among ALPGEN seen in higher order jets (N=0,1 vs. N=0-3)The difference among ALPGEN seen in higher order jets (N=0,1 vs. N=0-3)- Need much higher statistics for better understanding and quantitative estimationNeed much higher statistics for better understanding and quantitative estimation


Available samples (1)Available samples (1) in Univ. of Tokyoin Univ. of Tokyo

Towards the MC data validation / production, tons of events are being preparedTowards the MC data validation / production, tons of events are being prepared


Available samples (2)Available samples (2) in Univ. of Wisconsinin Univ. of Wisconsin

We need huge amount of samples to estimate SM background for SUSY !We need huge amount of samples to estimate SM background for SUSY !

Thanks to S. Padhi Thanks to S. Padhi (Univ. of Wisconsin-Madison)(Univ. of Wisconsin-Madison)


SummarySummary

ه ALPGEN, MC@NLO are compared in ALPGEN, MC@NLO are compared in tt+tt+Njets samplesNjets samplesه ALPGEN (N=0,1) resembles the Pt distribution of MC@NLOALPGEN (N=0,1) resembles the Pt distribution of MC@NLO

ه ALPGEN (N=0-3) has harder jets in higher order (2ALPGEN (N=0-3) has harder jets in higher order (2ndnd, 3, 3rd rd Pt Pt leading) jets leading) jets

ه It would be better to use ALPGEN for SUSY study??It would be better to use ALPGEN for SUSY study??

ه Pythia_i and Herwig_i needs to be compared carefullyPythia_i and Herwig_i needs to be compared carefully

ه Studies on Q scale, Matching condition dependences are important Studies on Q scale, Matching condition dependences are important

ه Huge amount of samples (ALPGEN and MC@NLO) are Huge amount of samples (ALPGEN and MC@NLO) are being prepared in ATLAS being prepared in ATLAS (waiting for validation and (waiting for validation and production)production)

mc validation: comparison alpgen vs. mc@nlo

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