background determination in early data for single electron trigger

e/ workshop in Hamburg

14-17 September 2008

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Background determination in early data for single electron

trigger

Oleg Fedin

• First look how to estimate background in early data and what useful can be extracted from first data

• Electron fake rate vs different physics processes

• Electron container:

Nel = Njets + Nconv + Nb,ce + NW,Z

Njets – fakes from jets

Nconv – conversion electrons (background electrons)

Nb,ce – electrons from b,c quarks (non isolated electrons)

NW,Z – electrons from W and Z decays (isolated electrons)

• Could we measure db,ce /dpT ?

• After tight cut (rel 13) :

• di-jet sample (5802 ET>17 GeV) Isolated 13% (W/Z~4:1); b,ce 58.3%; jet fakes 19.9%; conv. electrons 8.7%

• min. bias sample (5805 ET>8 GeV) b,ce 75.1%; jet fakes 18.5%; conv. electrons 6.4%

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• How to estimate jet fake contribution ? • TRT detector get possibility to identify electrons;• Varying TR ratio cut (#TR hits per track/#TRT hits

per track) try to suppress hadrons; • How to estimate conversion contribution?

• Conversion reconstruction algorithm (rel 14.2.20.2);• B-layer, E/p;

• How to estimate W,Z contribution?

• We ETmiss>25 GeV;

• Z ee events with two electrons;

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• egamma objects after tight cut

• TR ratio cut ~0.08 el~90%

~0.15 el~75%

5802 - di-jets

5802 - di-jets

5802 - di-jets-electrons- hadrons

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5805 - min bias

5805 - di-jets

• These plots most relevant to the first physics data (e10 trigger)

• To control background electrons relax B-layer and E/p cuts

• Purity = S/(S+B)• Signal (S) non isolated

electrons from b,ce • Background (B) include

jet fakes (hadrons) and conversion electrons

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5805 - min bias

5802 - di-jets

• Very difficult to extract separate contributions of b and c jets

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5802 - di-jets 5805 - min bias

Electron fake rates studies

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• Reminder: even in MC, fake rates from jets not yet understood as a function of physics processes

• Top plot - jets spectrum for the different data sample

• Bottom plot egamma object spectrum for the different data sample

DS5001 minbias (not filtr)DS5144 Z->eeDS5802 dijet (PT

Hard>15)DS5805 minbias (ET

filtr>6)DS5807 dijet (PT

Hard>35)

ETclus (GeV)

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• Illustration of kinematic ranges of truth jets and egamma objects in different physics sample

Jet rejection vs ETtruthJet

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DS5802 dijet (PTHard>15) ET

clus>17 GeVDS5805 minbias (ET

filtr>6) ETclus>8 GeV


clus>35 GeVDS5001 minbias (not filtr) ET

clus>8 GeVDS5009 dijet (PT

Hard=8-17) ETclus>8 GeV

DS5010 dijet (PTHard=17-35) ET



DS5144 Z->ee ETclus>8 GeV

• Clear seen threshold effects - compare di-jet data sample with PT

hard>35 (green triangle) and di-jet with PThard>17 (black

circle) • Jets spectrum due to QCD correction is more hard for Z->ee

data sample


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No cut on Etclus


clus>17 GeVDS5805 minbias (ET

filtr>6) ETclus>8 GeV


clus>35 GeVDS5001 minbias (not filtr) ET



DS5010 dijet (PTHard=17-35) ET



DS5144 Z->ee ETclus>8 GeV

Jet rejection vs ETcut

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DS5802 dijet (PTHard>15)

DS5805 minbias (ETfiltr>6)

DS5807 dijet (PTHard>35)

DS5001 minbias (not filtr)

DS5144 Z->ee

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Z-> eeDS5144

Min. bias DS5001

ETtruthjet> 8 GeV

Jet per event 2.82 0.62

light quark,% 32.3 25.4

b,c quark,% 8.8 6.7

gluon,% 54.4 62.7

not matched,% 4.5 5.2

ETtruthjet> 30 GeV

Jet per event 1.09 0.2

light quark,% 36.1 30.1

b,c quark,% 10.2 6.8

gluon,% 50.3 59.1

not matched,% 3.3 4.0

DS5001 Min bias

DS5144 Z->ee

• Matching truth jets to original parton quite complex (and frequently impossible

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Only gluon jets

light quark jets

b,c quark jets

• Need to understand why min bias Rg/Rq ~ 3 and Z->ee Rg/Rq ~ 2 and

BACK UP SLIDES

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Process DSPT

Hard, GeV

Filter,ET

jet

Eff. Filter,%

#Mevents

Cut ET

clus FRejection, medium cut

di jets 5802 >15 >17 8.28 8.4 >8 2.155 10012

>17 0.736 201810

di jets 5009 8-17 no 0.9 >8 0.955 156867

di jets 5010 17-35 no 0.4 >8 2.488 4228

>17 0.920 2953266

di jets 5011 35-70 no 2.8 >8 3.439 1511

>35 0.905 281693

di jets 5807 no >35 16.18 2.6 >8 3.056 6912

>17 1.862 9525

>35 0.862 189822

min bias 5805 no >6 5.7 4.1 >8 0.307 11728

>17 0.043 283986

min bias 5001 no no 3.2 >8 0.314 115539

>17 0.042 2307302

Z->ee 5144 no ETlep>10 0.2 >8 1.730 1292

>17 0.664 1143


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Etclus > 8 GeV

Jet rejection vs ETClus

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background determination in early data for single electron trigger

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