Short title Jun Huang Motivation Study of signal modelling uncertainties in t ¯ t Introduction up/dn production cross-section measurement at the isr-jetn isr-HT ATLAS experiment fsr-jetn fsr-HT analysis 4 variations isr-jetn Jun Huang isr-HT fsr-jetn fsr-HT University of Goettingen analysis total supervised by Prof. Arnulf Quadt ISR FSR analysis July 17, 2020 Conclusion Outlook 1 / 22
Short title 1-Motivation Jun Huang Motivation ◮ A precise measurement of t ¯ t production cross-section at Introduction √ s =13 Tev with the ATLAS experiment has been up/dn isr-jetn performed 1 . isr-HT fsr-jetn The result showed that the dominant theoretical fsr-HT analysis uncertainty originates from the t ¯ t signal modelling. 4 variations ◮ The measurement used the ATLAS recommendation to isr-jetn isr-HT estimate the different components in the signal fsr-jetn fsr-HT modelling uncertainty using old approach . analysis total ◮ My work is to investigate a new approach in handling ISR uncertainties, and compare it to the old one in terms of FSR analysis impact on the total uncertainty. Conclusion Outlook 1 https://arxiv.org/pdf/2006.13076.pdf 2 / 22
Short title 2.1-Introduction of old and new approach Jun Huang ◮ The old approach was, to make just individual changes Motivation of Var 3 c for initial and alphas for final state radiation. Introduction ◮ The new approach is to use kernel splitting weights up/dn - each splitting in the shower is evaluated for changes in isr-jetn isr-HT α FSR . This is done for each kind of splitting fsr-jetn s fsr-HT individually.Below meaning of variations: analysis 4 variations isr-jetn isr-HT G 2 GG g − → gg fsr-jetn fsr-HT G 2 QQ g − → q ¯ q analysis Q 2 QG q − → qg total X 2 XG gluon bremsstrahlung off ISR FSR other types of particles analysis Conclusion Outlook ◮ Uncertainties components: up/down, 4 variations, ISR/FSR 3 / 22
Short title 2.2 Introduction to my study Jun Huang Motivation ◮ Study t ¯ Introduction t MC samples and the systematic uncertainties up/dn due to variations of the parton shower isr-jetn ◮ Generator is Powheg+Pythia8. isr-HT fsr-jetn fsr-HT ◮ Study in the lepton+jets selection of ttbar events with analysis one electron or muon and 4 jets in the final state (on 4 variations isr-jetn reconstruction level). isr-HT fsr-jetn ◮ Selection criteria: reconstructed lepton with P T > 25 fsr-HT analysis GeV. total ◮ Investigate uncertainties contribution from all ISR FSR uncertainties components and comparison between old analysis Conclusion and new approach Outlook 4 / 22
Short title 3.1-Explanation of methods in comparison Jun Huang between up/dn variation Motivation Focus on jet n and HT plots: Introduction ◮ Axis Label: up/dn ratio plot : set Up as baseline, divide Down to Up to isr-jetn calculate the ratio between Down/Up. isr-HT fsr-jetn = ⇒ get relative correlation and difference fsr-HT analysis ◮ Legend value: 4 variations histo total uncertainty : adding uncertainties of each isr-jetn isr-HT bin linearly together. fsr-jetn fsr-HT = ⇒ get whole uncertainty analysis ratio total uncertainty : adding ratio value of each bin total ISR quadrature and dividing bin amount. FSR analysis = ⇒ get relative uncertainty Conclusion ◮ Y-axis-range in ratio plot: Outlook provide ratio range between [0.9:1.1], [0.95:1.05], [0.99:1.01] to improve the visibility of the error bands and make analysis more easier, accurate and meaningful. 5 / 22
N jets plots in ISR : G2GG > Q2QG > G2QQ > X2XG Short title × 3 × 3 10 10 Jun Huang Events Events isr_G2GG_muR_up/jet_n isr_G2QQ_muR_up/jet_n 600 isr_G2GG_muR_dn/jet_n 600 isr_G2QQ_muR_dn/jet_n histo total uncertainty is 6.8e+03 histo total uncertainty is 6.8e+02 Motivation ratio total uncertainty is 1.4% ratio total uncertainty is 0.091% 500 500 Introduction 400 400 up/dn 300 300 isr-jetn isr-HT 200 200 fsr-jetn fsr-HT 100 100 analysis 1.01 dn/up 1.1 dn/up 4 variations 1.05 1.005 1 1 0.95 0.995 isr-jetn 0.9 0.99 4 6 8 4 6 8 isr-HT jet_n jet_n fsr-jetn 3 fsr-HT × 3 × 10 10 Events Events analysis isr_Q2QG_muR_up/jet_n isr_X2XG_muR_up/jet_n 600 isr_Q2QG_muR_dn/jet_n 600 isr_X2XG_muR_dn/jet_n total histo total uncertainty is 2.1e+03 histo total uncertainty is 4.3e+02 ratio total uncertainty is 0.54% ratio total uncertainty is 0.033% 500 500 ISR FSR 400 400 analysis Conclusion 300 300 Outlook 200 200 100 100 1.01 dn/up dn/up 1.04 1.02 1.005 1 1 0.98 0.995 0.96 0.99 4 6 8 4 6 8 6 / 22 jet_n jet_n
H T plots in ISR : G2GG > Q2QG > G2QQ > X2XG Short title × 10 3 × 10 3 Jun Huang Events Events 160 160 isr_G2GG_muR_up/HT isr_G2QQ_muR_up/HT isr_G2GG_muR_dn/HT isr_G2QQ_muR_dn/HT 140 140 histo total uncertainty is 6.8e+03 histo total uncertainty is 6.8e+02 Motivation ratio total uncertainty is 0.17% ratio total uncertainty is 0.021% 120 120 Introduction 100 100 up/dn 80 80 isr-jetn 60 60 isr-HT 40 40 fsr-jetn fsr-HT 20 20 analysis 0 0 1.01 dn/up dn/up 1.04 4 variations 1.02 1.005 1 1 0.98 0.995 isr-jetn 0.96 0.99 0 500 1000 1500 0 500 1000 1500 isr-HT HT/[GeV] HT/[GeV] fsr-jetn × 3 × 10 3 10 fsr-HT Events Events 160 160 analysis isr_Q2QG_muR_up/HT isr_X2XG_muR_up/HT isr_Q2QG_muR_dn/HT isr_X2XG_muR_dn/HT 140 140 total histo total uncertainty is 2.1e+03 histo total uncertainty is 4.3e+02 ratio total uncertainty is 0.13% ratio total uncertainty is 0.011% 120 120 ISR FSR 100 100 analysis 80 80 Conclusion 60 60 Outlook 40 40 20 20 0 0 1.01 dn/up dn/up 1.04 1.02 1.005 1 1 0.98 0.995 0.96 0.99 0 500 1000 1500 0 500 1000 1500 7 / 22 HT/[GeV] HT/[GeV]
N jets plots in FSR: X2XG > G2GG > G2QQ > Q2QG Short title × 3 × 3 10 10 Jun Huang Events Events fsr_G2GG_muR_up/jet_n fsr_G2QQ_muR_up/jet_n 600 fsr_G2GG_muR_dn/jet_n 600 fsr_G2QQ_muR_dn/jet_n histo total uncertainty is 1.8e+04 histo total uncertainty is 1e+04 Motivation ratio total uncertainty is 0.42% ratio total uncertainty is 0.75% 500 500 Introduction 400 400 up/dn 300 300 isr-jetn isr-HT 200 200 fsr-jetn fsr-HT 100 100 analysis dn/up dn/up 4 variations 1.04 1.04 1.02 1.02 1 1 0.98 0.98 isr-jetn 0.96 0.96 4 6 8 4 6 8 isr-HT jet_n jet_n fsr-jetn fsr-HT × 3 × 3 10 10 Events Events 700 analysis fsr_Q2QG_muR_up/jet_n fsr_X2XG_muR_up/jet_n 600 fsr_Q2QG_muR_dn/jet_n fsr_X2XG_muR_dn/jet_n 600 total histo total uncertainty is 6.6e+03 histo total uncertainty is 6.4e+04 ratio total uncertainty is 0.2% ratio total uncertainty is 0.98% 500 ISR 500 FSR 400 400 analysis Conclusion 300 300 Outlook 200 200 100 100 dn/up dn/up 1.1 1.04 1.02 1.05 1 1 0.98 0.95 0.96 0.9 4 6 8 4 6 8 8 / 22 jet_n jet_n
H T plots in FSR: X2XG > G2GG > G2QQ > Q2QG Short title × 3 × 10 3 10 Jun Huang Events Events 160 160 fsr_G2GG_muR_up/HT fsr_G2QQ_muR_up/HT fsr_G2GG_muR_dn/HT fsr_G2QQ_muR_dn/HT 140 140 histo total uncertainty is 1.8e+04 histo total uncertainty is 1e+04 Motivation ratio total uncertainty is 0.26% ratio total uncertainty is 0.18% 120 120 Introduction 100 100 up/dn 80 80 isr-jetn 60 60 isr-HT 40 40 fsr-jetn fsr-HT 20 20 analysis 0 0 dn/up dn/up 1.04 1.04 4 variations 1.02 1.02 1 1 0.98 0.98 isr-jetn 0.96 0.96 0 500 1000 1500 0 500 1000 1500 isr-HT HT/[GeV] HT/[GeV] fsr-jetn × 10 3 × 10 3 fsr-HT Events Events 160 160 analysis fsr_Q2QG_muR_up/HT fsr_X2XG_muR_up/HT fsr_Q2QG_muR_dn/HT fsr_X2XG_muR_dn/HT 140 140 total histo total uncertainty is 6.6e+03 histo total uncertainty is 6.4e+04 ratio total uncertainty is 0.087% ratio total uncertainty is 0.39% 120 120 ISR FSR 100 100 analysis 80 80 Conclusion 60 60 Outlook 40 40 20 20 0 0 1.1 dn/up dn/up 1.04 1.02 1.05 1 1 0.98 0.95 0.96 0.9 0 500 1000 1500 0 500 1000 1500 9 / 22 HT/[GeV] HT/[GeV]
Short title 3.2-Conclusion of comparison between up/dn of Jun Huang 4 variations General conclusion Motivation Introduction ◮ Compare between electron and muon: similar behaviour up/dn ◮ Common uncertainty relation between up/dn of 4 isr-jetn isr-HT variations: fsr-jetn fsr-HT ISR: G2GG > Q2QG > G2QQ > X2XG analysis 4 variations FSR: X2XG > G2QQ > G2GG > Q2QG isr-jetn ◮ G2GG contribute the largest uncertainties in ISR and isr-HT fsr-jetn X2XG in FSR fsr-HT analysis total Anomalies ISR FSR ◮ G2GG sometime contribute the second largest analysis uncertainties and G2QQ the third in FSR Conclusion Outlook = ⇒ Unusual uncertainty relation in H T plots of G2GG and G2QQ could be caused by large uncertainties around 1400 GeV. 10 / 22
Short title 4.1-Explanation of methods in comparison Jun Huang between 4 variations impact on nominal Motivation histograms Introduction up/dn isr-jetn isr-HT Focus on error bars in N jets and H T plots: fsr-jetn fsr-HT ◮ Error bars on histograms for each bin: analysis 4 variations For single variation : Difference between variation and isr-jetn isr-HT nominal. fsr-jetn fsr-HT ◮ Error bars on ratio-plots for each bin: analysis difference between variation and nominal divided by the total ISR bin content, show the relative uncertainty FSR analysis ◮ Sometimes error bars and axis scales will overlap Conclusion Outlook 11 / 22
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