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V+jets in ATLAS Mein Text Text Mein Text Mein Text

V+jets in ATLAS Production of jets in association with W/Z bosons: /W Measurement of perturbative QCD Tuning of LO MonteCarlo generators Irreducible background to searches, Higgs selection ATLAS-COM-CONF-203-02 ATLAS-COM-CONF-202-60

First ATLAS measurements ATLAS 36 pb-: W/Z + up to 4 light jets. Comparison - fixed-order NLO (BlackHat+Sherpa) - generator predictions (ME+PS) ATLAS Z+jets 36pb- Z+jets: Phys. Rev. D85 (202) 032009, W+jets: Phys. Rev. D85 (202) 092002 W+jets/Z+jets: Phys.Lett.B 708 (202) 22-24 data mainly in agreement with theory, tensions in extreme phase space first input for generator tuning W+3jets: C. F. Berger et al., Phys. Rev. D 80, 074036 (2009) W+4jets: C. F. Berger et al., Phys. Rev. Lett. 060, 9200 (20) Z+3jets: C.F.Berger et al, Phys.Rev. D82 (200) 074002 Z+4jets: H. Ita et al, Phys.Rev. D85 (202) 0350

First ATLAS measurements ATLAS 36 pb-: W/Z + up to 4 light jets. Comparison - fixed-order NLO (BlackHat+Sherpa) - generator predictions (ME+PS) ATLAS W+jets 36pb Z+jets: Phys. Rev. D85 (202) 032009, W+jets: Phys. Rev. D85 (202) 092002 W+jets/Z+jets: Phys.Lett.B 708 (202) 22-24 data mainly in agreement with theory, tensions in extreme phase space first input for generator tuning W+3jets: C. F. Berger et al., Phys. Rev. D 80, 074036 (2009) W+4jets: C. F. Berger et al., Phys. Rev. Lett. 060, 9200 (20) Z+3jets: C.F.Berger et al, Phys.Rev. D82 (200) 074002 Z+4jets: H. Ita et al, Phys.Rev. D85 (202) 0350

First ATLAS measurements ATLAS 36 pb-: W/Z + up to 4 light jets. Comparison - fixed-order NLO (BlackHat+Sherpa) - generator predictions (ME+PS) ATLAS W+jets 36pb- Z+jets: Phys. Rev. D85 (202) 032009, W+jets: Phys. Rev. D85 (202) 092002 W+jets/Z+jets: Phys.Lett.B 708 (202) 22-24 data mainly in agreement with theory, tensions in extreme phase space first input for generator tuning W+3jets: C. F. Berger et al., Phys. Rev. D 80, 074036 (2009) W+4jets: C. F. Berger et al., Phys. Rev. Lett. 060, 9200 (20) Z+3jets: C.F.Berger et al, Phys.Rev. D82 (200) 074002 Z+4jets: H. Ita et al, Phys.Rev. D85 (202) 0350

New Z+jets measurement New ATLAS Z+jets measurement with 4.6fb- of data collected at s = 7TeV Extreme phase space: Large jet multiplicity, pt(z), pt(jet)/ht Perturbative QCD: large higher order corrections, large logarithms Match searches phase space: large pt(leading jet), H T, pt(z), m(jj), Δy(jj)... Large pt( jet), large HT Large pt(z): - Large QCD corrections ~αs ln2( pt(jet) / mz ) Z recoils vs several jets Large EW NLO corrections Larger jet multiplicities Differential distributions for Z+3/4jets

Extraction of cross section Reconstruction of Z ee, Z μμ, jets Subtraction of backgrounds (2-20%) Top: dominating for 2jets, from data (eμ) Z+3-6 jets: ~5-8% (W+jets: ~30-85%! ) other: Multi-jets, diboson, V+jets Top background extraction from e+μ final states Leptons: pt > 20 GeV, η < 2.5 add photons in ΔR<0. Z -Boson : Opposite sign leptons, 66 < m(ll) < 6 GeV Jets: antikt, R=0.4, ΔR(j,l) < 0.5 pt > 30 GeV, y < 4.4

Extraction of cross section Reconstruction of Z ee, Z μμ, jets Subtraction of backgrounds (2-20%) Top: dominating for 2jets, from data (eμ) Z+3-6 jets: ~5-8% (W+jets: ~30-85%! ) other: Multi-jets, diboson, V+jets Dominating uncertainty: jet energy scale: 7-7% Leptons: pt > 20 GeV, η < 2.5 add photons in ΔR<0. Z -Boson : Opposite sign leptons, 66 < m(ll) < 6 GeV Jets: antikt, R=0.4, ΔR(j,l) < 0.5 pt > 30 GeV, y < 4.4

Theory predictions BlackHat+Sherpa NLO: Z ( ll) + 0//2/3/4jets PDF: CT0, Ren/fac scale HT/2 + Corrections for non-perturbative effects: Fragmentation + Underlying Event: 3-4% + QED correction: Born dressed leptons: 2% Uncertainties: Scale PDF: αs variation: 4-3% -3% : -3% Dressing: add γ in R<0.

Jet multiplicities Test of QCD IS/FS QCD radiation Potentially sensitve to s NLO: Higgs/Top, searches: decay jets + QCD radiation QCD background QCD radiation in signal up to 4 ( 5) jets, higher multiplicities at LO ME+PS generators benchmark predictions from first principles (Phys. Lett. B 224 (989) 237, JHEP 20 (202) 62) QED: Abelian-type FSR QCD: Non-abelian FSR ~ /n ~ const expect R~/n for large scale differences

Inclusive jet multiplicities Unfolded data compared with: BlackHat+Sherpa fixed-order NLO pqcd C.F.Berger et al, Phys.Rev. D82 (200) 074002 H. Ita et al, Phys.Rev. D85 (202) 0350 ALPGEN+HERWIG+JIMMY (Z+0-5p) AUET2 tune, CTEQ6L PDF global NNLO k-factor Sherpa.4 MENloPS (Z+0-5p) CT0 PDF, global NNLO k-factor MC@NLO (Drell-Yan) +HERWIG AUET2 tune, CT0 PDF, NNLO k-factor Differential cross sections normalized to inclusive cross section: Cancel uncertainties Well modelled by pqcd and ME+PS

Inclusive jet multiplicities Multiplicity ratios: improved exp. precission Well modelled by pqcd and ME+PS

Exclusive jet multiplicities Scale uncertainties calculated using inclusive scale variations, scale uncertainties assumed to be uncorrelated wrt multiplicity I.W.Stewart, F.J. Tackmann Phys. Rev. D 85 (202) 0340 Naive scale variation, correlated uncertainties no scale variation Well modelled by fixed-order NLO pqcd with nominal scale (HT/2)

Benchmarkscaling patterns pt(jets) > 30 GeV ~ const pt(jet ) > 50 GeV ~ /n Staircase / Poisson scaling benchmarks for equal jet pt / large jet pt differences Change of scaling pattern in modelled by nominal pqcd and ME+PS

Z, jet transverse momenta Large jet and Z transverse momenta - signal tolopolies in searches - expect large QCD and EW effects EW NLO effects QCD higher-order effects ~ Large pt(z), pt(jet), 2nd jet resolved Can we separate both effects? - large pt(z): Collinear jets - large pt(jet): Jets recoil vs boosted Z Dijet event radiates Z A.Denner et al, JHEP06 (20) 069

pt(jet) and pt(z) pt(jet ) > 50 GeV: 2nd jet in 50% of evts NLO consistent with data, tends to undershoot Alpgen too hard higher-order QCD/EW? pt(jz) >200 GeV: <njet> = 2 Similar trends for pt(z)

V+jets in ATLAS Compare with exclusive Z+jet: Z jet topology Alpgen closer to data combination of QCD and EW effects?

pt(jet3), pt(jet 4) PT (jet 3) PT (jet 4) NLO Z+ 3(4) jets and ME+PS consistent with data

Inclusive Observables HT and ST in V+jets QCD scale choice Important for searches: signal topologies with large jet activity <Njet> increasing with HT ATLAS-COM-CONF-203-02 problems with fixed- order NLO

HT and ST HT (Z+ jet) ST (Z+ jet) Fixed-order NLO Z+ jet underestimates large HT/ST ALPGEN consistent with data

HT: exclusive sums Exclusive sum Z+jet and Z+ 2jets improves description of HT Improves also pt(z) description Les-Houches 20, multi-leg summary report: http://arxiv.org/abs/203.6803

Angular distributions Important for Higgs selections, in particular VBF production: large m(jj), large (Dy(jj) veto central jet activity Experimental challenge: - Large JES uncertainty in forward region - Pile-up effects QCD test: - Jet angular relations - pt(jet) in forward regime - central jet activity ATLAS-COM-CONF-202-60

Jet angular distributions y (jet ) y (jet,jet 2) Jet rapidity: NLO and Sherpa overestimate large rapidity (jet, jet 2) Large distance in rapidity: NLO ok, ALPGEN too low, Sherpa too wide

Jet angular distributions Φ (jet,jet 2) m(jet,jet 2) NLO and ME+PS consistent with data, some trends in m(jj)

rd th Rapidity of 3 and 4 jet y (jet 3) y (jet 4) y (jet 3), y (jet 4): Cover larger range with higher precision NLO and ME+PS consistent with data

VBF-type preselection Preselection: m(jj) >350GeV Δy(jj) >3.0 Excl. jet multiplicity y (jet 3) pt(jet) NLO and ME+PS consistent with data

V+light jets summary Production of jets in association with W/Z boson in more extreme phase space regions Z+4(5) jets well modelled by NLO pqcd and ME+PS PS alone so far no good description Different slopes in data and theory for pt(jet) and pt(z) indicate higher-order EW or higher-order QCD effects Angular relations of importance in Higgs searches in general modelled well, problems of pnlo and Sherpa in large jet rapidities Modelling of inclusive quantities like HT, ST, pt(z) over various jet multiplicities can be improved by exclusive sums of NLO calculations ( nnlo)

V+jets in ATLAS Mein Text Text Mein Text Mein Text

Jet transverse momentum PT (jet 2) PT (jet 2) / PT (jet) NLO pqcd consistent with data, small slope ALPGEN overestimates events with small PT (jet2)/pt(jet)