Radiating top quarks

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Gosselink, M.

Publication date 2010

Link to publication

Citation for published version (APA):

Gosselink, M. (2010). Radiating top quarks.

http://www.nikhef.nl/pub/services/biblio/theses_pdf/thesis_M_Gosselink.pdf

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B

Generator comparison

B.1 MC@NLO, Alpgen, and AcerMC

The following figures show comparisons between MC@NLO, Alpgen, and AcerMC of the transverse momentum distributions of top quarks, t¯t pairs, and jets in semi-leptonic

t¯t events at √s = 14 TeV. All distributions are normalised to unity.

[1/0.1 GeV] _T /dp σ d × σ 1/ 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 [1/0.1 GeV] _T /dp σ d × σ 1/ 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia (top) ) [GeV] T ( p 10 log -0.5 0 0.5 1 1.5 2 2.5 3 ratio 0.5 1.0 1.5 (top) ) [GeV] T ( p 10 log -0.5 0 0.5 1 1.5 2 2.5 3 ratio 0.5 1.0 1.5 [1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia (top) [GeV] T p 0 100 200 300 400 500 ratio 0.5 1.0 1.5 (top) [GeV] T p 0 100 200 300 400 500 ratio 0.5 1.0 1.5

Figure B.1: Transverse momentum of the top quarks.

[1/0.1 GeV] _T /dp σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 [1/0.1 GeV] _T /dp σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia ) ) [GeV] t (t T ( p 10 log -0.5 0 0.5 1 1.5 2 2.5 3 ratio 0.51.0 1.5 ) ) [GeV] t (t T ( p 10 log -0.5 0 0.5 1 1.5 2 2.5 3 ratio 0.51.0 1.5 [1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia ) [GeV] t (t T p 0 100 200 300 400 500 ratio 1.00.5 1.5 ) [GeV] t (t T p 0 100 200 300 400 500 ratio 1.00.5 1.5

Figure B.2: Transverse momentum of the top quark pair.

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Appendix B. Generator comparison Fraction of events 0.00 0.05 0.10 0.15 0.20 Fraction of events 0.00 0.05 0.10 0.15 0.20 MC@NLO/Herwig_{Alpgen/Herwig} AcerMC/Pythia jets N 0 5 10 15 ratio 0.5 1.0 1.5 jets N 0 5 10 15 ratio 0.5 1.0 1.5 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia [GeV] T jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 0.5 1.0 1.5 [GeV] T jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 0.5 1.0 1.5

Figure B.3: Jet spectrum and transverse momentum of all jets (pT > 7 GeV, |η| <5.0).

[1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia [GeV] T leading jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 1.00.5 1.5 [GeV] T leading jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 1.00.5 1.5 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia [GeV] T subleading jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 0.51.0 1.5 [GeV] T subleading jet p 0 50 100 150 200 250 300 350 400 450 500 ratio 0.51.0 1.5

Figure B.4: Transverse momentum of the leading and subleading jet.

[1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 [1/25.0 GeV] _T /dp σ d × σ 1/ -3 10 -2 10 -1 10 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia [GeV] T

leading extra jet p

0 50 100 150 200 250 300 350 400 450 500

ratio 1.00.5 1.5

[GeV]

T

leading extra jet p

0 50 100 150 200 250 300 350 400 450 500 ratio 1.00.5 1.5 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 1 [1/25.0 GeV] _T /dp σ d × σ 1/ -4 10 -3 10 -2 10 -1 10 1 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia [GeV] T

subleading extra jet p

0 50 100 150 200 250 300

ratio 0 2

[GeV]

T

subleading extra jet p

0 50 100 150 200 250 300

ratio 0 2

Figure B.5: Transverse momentum of the first and second extra jet (not from top de-cay).

B

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B.2. AcerMC/Pythia: ISR and FSR variation [1/0.4] η /d σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 [1/0.4] η /d σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia η

leading extra jet

-4 -2 0 2 4

ratio 0.5 1.0 1.5

η

leading extra jet

-4 -2 0 2 4 ratio 0.5 1.0 1.5 [1/0.4] η /d σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 [1/0.4] η /d σ d × σ 1/ 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MC@NLO/Herwig Alpgen/Herwig AcerMC/Pythia η

subleading extra jet

-4 -2 0 2 4

ratio 0.5 1.0 1.5

η

subleading extra jet

-4 -2 0 2 4

ratio 0.5 1.0 1.5

Figure B.6: Pseudo-rapidity of the first and second extra jet (not from top decay).

B.2 AcerMC/Pythia: ISR and FSR variation

Three different AcerMC/Pythia samples are available for the simulation of t¯t events with full detector simulation (Appendix A). The samples have different settings for the initial state radiation and final state radiation parameters:

‘005205’ with the default ATLAS settings;

‘006250’ with enhanced ISR and reduced FSR;

‘006251’ with reduced ISR and enhanced FSR.

The variation in ISR and FSR parameters leads to either a higher (006250) or a lower (006251) reconstructed hadronic top mass. The impact on the selection, reconstruction, and combined efficiency for the t¯t cross section measurement in Chapter 5 is demon-strated in Table B.1. Note the opposite effects on the selection and reconstruction effi-ciencies, which diminish the effect on the combined efficiency. This is similar to what is observed when varying the jet energy scale (Section 5.6.5).

sample muon channel electron channel

ǫǫǫsel ǫǫǫrec ǫǫǫcomb ǫǫǫsel ǫǫǫrec ǫǫǫcomb

005205 24.67 16.65 4.11 19.16 16.22 3.11

006250 27.45 15.86 4.36 21.27 15.75 3.35

006251 22.45 18.58 4.17 17.61 18.39 3.24

Table B.1: The selection, reconstruction, and combined efficiencies (in %) for t¯t events in the electron and muon channel for various ISR/FSR settings in AcerMC.

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