1. QCD estimate with the matrix method Alexander D. with the help of many…

2. overview samples & definitions the method ‘closure’ in mc results in data dealing with b-tag and triangular cut full results systematics: full story control plots conclusions 2 AtlasGroup - 29-10-2010 method top publication

3. all data up to F2 integrated luminosity = 2.89 pb -1 data: top d2pd’s + GRL (top_allchannels) MC: topmix sample (108179), qcdmix samples (108180,108181) base-selection (TopCommonObjects): muon-trigger, exactly one good muon, MET > 20 GeV, primary vertex, no bad jet samples & selections 3 AtlasGroup - 29-10-2010

4. the method relies on the distinction between loose and tight muons where we have isolated muons (ttbar, W+jets, Z+jets) and non-isolated muons (qcd) tight is a subset of loose tight is usually the final selection used in the analysis loose is usually kinematically the same as tight, but less or no quality requirements N L = N L R + N L F N T = N T R + N T F = ε R N L R + ε F N L F where ε is the efficiency for fake/real lepton to move from L(oose) to T(ight). this then yields: matrix method 4 AtlasGroup - 29-10-2010

5. measure what? where? N L is just the number of loose muons in your selected top-sample same for N T ε R has to come from a signal-muon dominated sample: Z  µµ same as for muons from top?  yes! same as in ttbar-environment?  yes! ε F will be measured using a QCD enriched sample: high d0 significance is the efficiency flat with respect to d0 significance? what about contamination from W’s, Z’s? 5 AtlasGroup - 29-10-2010

6. loose - tight Loose: MuId muons p T > 20 GeV |η| < 2.5 isTight (MCP flag) dR 20) Tight: Loose + etcone30 < 4 GeV + ptcone30 < 4 GeV ε the definitions should aim for: tight is dominated by signal-like muons loose is mainly QCD muons loose  tight as small as possible for QCD: best statistical precision 6 AtlasGroup - 29-10-2010

7. fake-efficiency AtlasGroup - 29-10-2010 7 measure the fake efficiency above d0 significance =5. Only slightly contaminated, hardly biasing QCD efficiency. MC: 0.30 ± 0.02 data: 0.30 ± 0.03 MC, 1 jet inclusive, topmix + qcdmix data, 1 jet inclusive

8. ‘closure’ in mc uncertainty in plot (grey area) from N L, N T, ε F and ε R in table: 1 st : N L, N T 2 nd : ε F, ε R closure is worst in 2 jet bin: 16% mc 10 pb -1 8 AtlasGroup - 29-10-2010 base-selection

9. data results base with jet > 25 MET > 20 1 j252 j253 j254j25 QCD 300.7 ± 11.4 ± 36.0 84.2 ± 6.1 ± 10.1 22.7 ± 3.2 ± 2.7 3.9 ± 1.4 ± 0.6 top 1.66.41319 rest 1486.8358.780.124 total estimate 1789.1449.4115.846.9 data events 193945511461 uncertainty in plot from N L, N T, ε F and ε R in table: 1 st : N L, N T 2 nd : ε F, ε R 9 AtlasGroup - 29-10-2010

10. dealing with b-tag & triangular cut problem: no events with d0 significance > 5. after triangular cut  no ε F only few events in general after b-tag & triangular cut: large uncertainties possible solutions: use the b-tag efficiency for QCD from mc per jet bin solution 1 use the b-tag efficiency for QCD from mc per jet bin solution 1 use ε F obtained before triangular cut solution 2 use ε F obtained before triangular cut solution 2 10 AtlasGroup - 29-10-2010 triangular cut = MET + M wtrans > 60 GeV

11. mc: solution 1 – b-tag about 100% from QCD muons are from HF (shown by truth studies) we trust that b-tagging is well modeled in mc per jet bin extra systematic: 30% b-tagging uncertainty this is the c-tag uncertainty at the moment, conservative extra uncertainty from limited QCD-mc statistics example in 4+ jet bin we have: tagged = 5.1 untagged = 8.6 b-tag efficiency = 59% ± 17% (stat.) ± 18% (b-tag uncertainty) total extra uncertainty: D closure: base + b-tag mc 10 pb -1 11 AtlasGroup - 29-10-2010

12. mc: solution 2 triangular cut we can use ε F obtained before triangular cut  cut does not change the probability that loose muon becomes tight. uncertainty in plot (grey area) from N L, N T, ε F and ε R base + triangular cut mc 10 pb -1 12 AtlasGroup - 29-10-2010  no extra systematic

13. solutions summary: 1: b-tag ▫we use the b-tag efficiency for QCD from mc to estimate QCD after b-tagging ▫assign 30% + mc-statistics uncertainty to this 2: triangular cut ▫we use ε F as obtained before triangular cut ▫no extra systematic from this due to good closure 1 + 2: for base + b-tag + triangular cut 13 AtlasGroup - 29-10-2010

14. data results base with jet > 25 +b-tag + triangular MET > 20 1 j252 j253 j254j25 QCD 3.5 ± 0.3 ± 0.4 1.9 ± 0.3 ± 0.2 0.7 ± 0.2 ± 0.1 0.9 ± 0.6 ± 0.2 top 0.63.68.112.6 rest 20.212.25.22.3 total estimate 24.417.714.115.7 data events 30 1819 uncertainty in plot from N L, N T, ε F and ε R in table: 1 st : N L, N T 2 nd : ε F, ε R 14 AtlasGroup - 29-10-2010 solution 1&2

15. we defined three main systematic uncertainties (additional to the error from the efficiencies). A: prompt contamination B: the control region variation C: closure test All these systematics after base selection without b-tagging to preserve some statistics. systematics 15 AtlasGroup - 29-10-2010 base selection

16. the full systematics table on data systematics on data 16 AtlasGroup - 29-10-2010 1 jet252 jet253 jet254+ jet25 contamination: A 1.8% control region: B 10.9% 11.0% closure: C 16.0% ε F and ε R 11.9%12.0%12.1%14.9% MC(ε R )2.0% total22.9%23.0% 24.6% statistics3.8%7.2%13.9%35.6% base selection

17. systematics: full story for each jet bin and cut we assign: A,B,C as discussed before D if the estimate is after b-tagging uncertainty from ε F and ε R 2% uncertainty for obtaining ε R from mc example for after b-tagging, triangular cut and for 4j25 (table slide 17): 0.884 ± 0.563(stat) ± 0.098(A,B) ± 0.141(C) ± 0.364(D) ± 0.223(ε F, ε R ) ± 0.018(ε R ) = 0.884 ± 0.563(stat) ± 0.461(syst) 17 AtlasGroup - 29-10-2010 A: prompt contamination B: control region C: closure test D: b-tag uncertainty A: prompt contamination B: control region C: closure test D: b-tag uncertainty base + btag + triangular cut

18. control plots - MET AtlasGroup - 29-10-2010 18 qcd uncertainty = statistics + systematics base selection, 2 jet exclusive bin:base + triangular, 2 jet exclusive bin:

19. control plots - MET AtlasGroup - 29-10-2010 19 qcd uncertainty = statistics + systematics base selection + btag, 2 jet exclusive bin: base + btag + triangular, 2 jet exclusive:

20. control plots - M Wtrans AtlasGroup - 29-10-2010 20 qcd uncertainty = statistics + systematics base selection, 1 jet exclusive bin: base + triangular, 2 jet exclusive: KS-Test: 0.996KS-Test: 0.968 common normalization, muon smeared

21. control plots - M Wtrans AtlasGroup - 29-10-2010 21 qcd uncertainty = statistics + systematics base +btag + triangular, 2 jet exclusive: base +btag + triangular, 4 jet exclusive: KS-Test: 0.998 ! common normalization, muon smeared

22. conclusions AtlasGroup - 29-10-2010 22 we have tried various ways of saving the low statistics 2 solutions were presented: b-tag efficiency from mc (solution 1) getting ε F before triangular cut (solution 2) both solutions give nice closure in mc both solutions were applied on data samples  results look good we have presented the full picture of the systematic studies PlotQCD.C  makes the QCD data-driven plot for you! function: TH1D * qcd = PlotQCD(TH1D* loose, TH1D* tight, int IJet, int IBtag, int Ierror)  no more analysis for me… it’s all writing from here-on!

23. back-up slides

24. QCD Heavy Flavor Fraction Inclusive muon prompt component measured in ATLAS-CONF-2010-075 Data and MC in good agreement HF fraction is ~70% or 90% depending on eta region for 10 < pt < 20 GeV HF fraction will increase for our selections: Etmiss> 20 GeV, pt(mu)> 20 GeV, >=1-jet Prompt muon are from heavy flavor for this pt regime Conclusions: 24 AtlasGroup - 29-10-2010

25. solutions that didn’t work… AtlasGroup - 29-10-2010 25 using ε F obtained before b-tagging in the b-tagged sample: closure is not good in the 1,2 and 4j25 bin also observed difference in measure efficiency in data, but uncertainties large use efficiency for QCD to pass triangular cut (ε triang ) from mc: qcd mc: in 1 jet exclusive (base-cuts): ε triang = 9% topmix + qcdmix, 1 jet bin, base cuts, d0 sig > 5: ε triang = 22% data, 1 jet bin, base cuts, d0 sig > 5: ε triang = 38%  ε triang from mc cannot be used to extrapolate base + b-tag, 10pb -1 mc

26. data results base with jet > 25 +b-tag MET > 20 1 j252 j253 j254j25 QCD 21.0 ± 0.8 ± 2.5 10.9 ± 0.8 ± 1.3 3.5 ± 0.5 ± 0.4 2.3 ± 0.8 ± 0.3 top 0.749.414.2 rest 2212.95.82.6 total estimate 43.727.818.719.1 data events 49382021 uncertainty in plot from N L, N T, ε F and ε R in table: 1 st : N L, N T 2 nd : ε F, ε R 26 AtlasGroup - 29-10-2010 solution 1

27. data results base with jet > 25 + triangular cut MET > 20 1 j252 j253 j254j25 QCD 50.6 ± 4.9 ± 6.1 14.5 ± 2.7 ± 1.8 4.7 ± 1.5 ± 0.7 1.5 ± 0.9 ± 0.4 top 1.55.711.216.8 rest 1399.1334.973.421.9 total estimate 1451.2355.189.340.1 data events 15563679755 uncertainty in plot from N L, N T, ε F and ε R in table: 1 st : N L, N T 2 nd : ε F, ε R 27 AtlasGroup - 29-10-2010 solution 2

28. transverse W-mass: KS-Test: Kolmogorov-Smirnov Test. A non-parametric test for the equality of distributions. definitions AtlasGroup - 29-10-2010 28