1. W/Z+jets Background Determination in the ATLAS ICHEP SUSY Notes
Dan Tovey
University of Sheffield 1

2. ATLAS ICHEP SUSY Notes 2

3. 0-lepton Analysis 3

4. 0-lepton Analysis
NO ETmiss cut
With ETmiss cut 4

5. 0-lepton Analysis 5

6. 1-lepton Analysis 6

7. Monte Carlo Samples ALPGEN multi-parton ME MC with CTEQ6L1 LO PDF set
0 – 5 parton samples (0 - 4 parton excl, 5 parton inclusive)
MLM matching: ETclus = 20 GeV, ΔRmatch = 0.7
Herwig + Jimmy for PS and UE
Wlν and Zll (m(ll) cut) unbiased
Zνν : filter requiring at least one Anti-KT(0.4) truth-jet with pT>25 GeV in |η| < 5
Low mass DY for dilepton analysis uses PYTHIA (m(ll) cut) 7

8. Normalisation
Ultimately aim to obtain this where possible with data-aware / driven / validated techniques (see next talk)
1-lepton analysis W+jets: use control region enriched in W+jet events
30 GeV < ETmiss < 50 GeV
40 GeV < mT(l, ν) < 80 GeV
Overall normalisation 2.1 ± 1.0
Apply normalisation factor to signal region with assumed 50 % total uncertainty
Z+jets backgrounds normalised to cross-section
Ditto W/Z+jets in 0-lepton analysis
QCD jet estimate normalised in control region with ETmiss cut removed 8

9. Control Region
No mT cut
No mT cut
No ETmiss cut
No ETmiss cut 9

10. W+jets Normalisation
W+jets (0-lepton analysis): normalise to NNLO prediction using FEWZ with MSTW2008 PDF set
10.45 nb
k-factor = 1.20 with respect to ALPGEN LO cross-section
Expect ~3% uncertainty from PDF and scale choice
Luminosity uncertainty 11% 10

11. Z+jets Normalisation
Z+jets: normalise to NNLO prediction using FEWZ with MSTW2008 PDF set
Z(νν): 5.82 nb
k-factor = 1.28 with respect to ALPGEN LO cross-section
Z(ll): 0.79 nb (per channel, m(ll)>60 GeV)
Expect ~3% uncertainty from PDF and scale choice
Luminosity uncertainty 11% 11