High-precision predictions for V+jet production Jonas M. Lindert - PowerPoint PPT Presentation

High-precision predictions for V+jet production Jonas M. Lindert work in collaboration with: 
 R. Boughezal, A. Denner, S. Dittmaier, A. Huss, A. Gehrmann-De Ridder, 
 T. Gehrmann, N. Glover, S. Kallweit, P. Maierhöfer, M. L. Mangano, 
 T.A. Morgan, A. Mück, M. Schönherr, F. Petriello, S. Pozzorini, G. P. Salam UCL HEP Seminars 
 UCL, London, 21.04.2017

V + multijet production ‣ Dominant backgrounds for monojet DM searches ‣ Important/dominant backgrounds for various 
 BSM searches (lepton + missing E T + ets) ‣ Dominant backgrounds for top physics ‣ Dominant backgrounds for Higgs physics , e.g. VH( → bb), H → WW Standard Model Production Cross Section Measurements Status: July 2014 σ [pb] 10 11 80 µ b − 1 Run 1 √ s = 7, 8 TeV ATLAS Preliminary 10 6 0.1 < p T < 2 TeV LHC pp √ s = 7 TeV LHC pp √ s = 8 TeV ‣ Large cross-sections and clean leptonic signatures 0.3 < m jj < 5 TeV 10 5 Theory Theory 10 4 njet ≥ 0 Data 4.5 − 4.7 fb − 1 Data 20.3 fb − 1 ‣ 35 pb − 1 V+jets : Precision QCD at LHC 10 3 njet ≥ 1 njet ≥ 0 35 pb − 1 ‣ njet ≥ 2 njet ≥ 0 95% CL Playground to probe different aspects of higher-order 10 2 njet ≥ 1 upper limit njet ≥ 3 13.0 fb − 1 4.9 fb − 1 njet ≥ 2 0.7 fb − 1 calculations 
 10 1 2.0 fb − 1 njet ≥ 4 njet ≥ 4 njet ≥ 3 95% CL njet ≥ 5 (LO+PS, NLO+PS, NLO-Merging, NLO EW,…) 
 upper njet ≥ 5 1 limit njet ≥ 4 njet ≥ 6 1.0 fb − 1 njet ≥ 6 njet ≥ 7 njet ≥ 5 10 − 1 njet ≥ 8 njet ≥ 6 ‣ Probe and constrain PDFs 10 − 2 njet ≥ 7 njet ≥ 7 10 − 3 pp t t − chan t¯ t s − chan Jets Dijets W Z t¯ WW Wt WZ ZZ t γ W γ Z γ t¯ t¯ Zjj H → γγ t WW + γγ tW tZ W ± W ± jj WZ R=0.4 R=0.4 EWK EWK total fi ducial fi ducial total total total total fi ducial total total total fi ducial fi ducial fi ducial total total fi ducial fi ducial fi ducial total | y | < 3.0 | y | < 3.0 y ∗ < 3.0 njet=0 njet=0 High-precision predictions for V+jet production Jonas M. Lindert 2

V+jets backgrounds in monojet/MET + jets searches irreducible backgrounds: pp → Z( → νν̅ )+jets ⟹ MET + jets pp → W( → lv)+jets ⟹ MET + jets (lepton lost) 3 High-precision predictions for V+jet production Jonas M. Lindert

Target precision 10% 1% • for 500 GeV < pTV < 1000 GeV: background statistics will be at 1% level • understanding of V+jets backgrounds at this level increases sensitivity in DM searches • this level of precision is theoretically possible @ NNLO QCD + NNLO EW • requires solid understanding of uncertainties ! 4 High-precision predictions for V+jet production Jonas M. Lindert

Determine V+jets backgrounds global fit of Z( → l l ̅ )+jets, W( → l ν̅ )+jets and ɣ +jets measurements • to determine Z( →ν̅ν )+jet • and the visible channels at high-pT W( → l ν̅ )+jets • theory systematics (scales, etc.) via nuisance parameters in fit d σ /dpTV ɣ +jets Z( → l l ̅ )+jets Z( → ν̅ν )+jet pTV 1 TeV • hardly any systematics (just QED dressing) • fairly large data samples at large pT • very precise at low pT • systematics from transfer factors • but: limited statistics at large pT 5 High-precision predictions for V+jet production Jonas M. Lindert


 
 
 
 
 
 
 
 Goal of the ongoing study [to be published soon, already available to ATLAS & CMS] • Combination of state-of-the-art predictions: (N)NLO QCD+(N)NLO EW 
 in order to match (future) experimental sensitivities 
 (1-10% accuracy in the few hundred GeV-TeV range) 
 d x � ( V ) " # d TH ( ~ " TH ) d d " TH ) := d d y � ( V ) y � ( V ) ( ~ " MC , ~ MC ( ~ " MC ) d x � ( V ) d x d ~ d x d ~ d MC ( ~ " MC ) parameter x um, x = p ( V ) one-dimensional reweighting of MC samples in T , dence of the d TH = d QCD + d mix + d EW + d with d x � ( V ) d x � ( V ) d x � ( V ) d x ∆ � ( V ) d x � ( V ) γ − ind . . • Robust uncertainty estimates including • Prescription for correlation of these uncertainties 1.Pure QCD uncertainties ‣ within a process (between low-pT and high-pT) 2.Pure EW uncertainties ‣ across processes 3.Mixed QCD-EW uncertainties 4.PDF, ɣ -induced uncertainties …. High-precision predictions for V+jet production Jonas M. Lindert 6

Prelude: Z+jet vs. ɣ + 1 jet pp → Z + 1j @ 13 TeV pp → Z + 1j @ 13 TeV pp → γ + 1j @ 8 TeV pp → γ + 1j @ 8 TeV 10 3 10 3 10 3 10 3 Munich+OpenLoops Munich+OpenLoops Munich+OpenLoops Munich+OpenLoops ɣ +jet 10 2 10 2 10 2 10 2 preliminary! preliminary! preliminary! preliminary! Z+jet d σ / d p T , Z [fb / GeV] d σ / d p T , Z [fb / GeV] d σ / d p T , γ [fb / GeV] d σ / d p T , γ [fb / GeV] 10 1 10 1 10 1 10 1 ∆ φ ( j 1 , j 2 ) < 2 . 5 ∆ φ ( j 1 , j 2 ) < 2 . 5 ∆ φ ( j 1 , j 2 ) < 2 . 5 ∆ φ ( j 1 , j 2 ) < 2 . 5 10 0 10 0 10 0 10 0 10 − 1 10 − 1 10 − 1 10 − 1 10 − 2 10 − 2 LON 10 − 2 10 − 2 LON NLO QCD NLO QCD 10 − 3 10 − 3 NLO QCD+EW 10 − 3 10 − 3 NLO QCD+EW NLO QCD × EW NLO QCD × EW 1.1 1.1 1.1 1.1 1 1 1 1 0.9 0.9 QCD QCD d σ / d σ NLO d σ / d σ NLO 0.9 0.9 d σ / d σ NLO d σ / d σ NLO QCD QCD 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.5 0.5 0.5 0.5 250 250 500 500 750 750 1000 1000 1250 1250 1500 1500 500 500 1000 1000 1500 1500 p T , Z [GeV] p T , Z [GeV] p T , γ [GeV] p T , γ [GeV] EW corrections QCD corrections ‣ correction in pT(Z) > correction in pT( ɣ ) ‣ mostly moderate and stable QCD corrections ‣ (almost) identical QCD corrections in the tail , 
 ‣ -20/-8% for Z/ ɣ at 1 TeV sizeable differences for small pT ‣ EW corrections > QCD uncertainties for p T,Z > 350 GeV High-precision predictions for V+jet production Jonas M. Lindert 7

Prelude: Z/ ɣ pT-ratio pp → Z / γ + 1j @ 8 TeV pp → Z / γ + 1j @ 8 TeV 0 . 3 0 . 3 Overall d φ ( j 1 , j 2 ) < 2 . 5 d φ ( j 1 , j 2 ) < 2 . 5 Munich+OpenLoops Munich+OpenLoops 0 . 28 0 . 28 preliminary! preliminary! ‣ mild dependence on the boson pT ν / d σ γ j ν / d σ γ j 0 . 26 0 . 26 d σ Zj × BR Z → ν ¯ d σ Zj × BR Z → ν ¯ 0 . 24 0 . 24 0 . 22 0 . 22 QCD corrections 0 . 2 0 . 2 LON ‣ 10-15% below 250 GeV NLO QCD 0 . 18 0 . 18 NLO QCD+EW ‣ ≲ 5% above 350 GeV NLO QCD × EW 0 . 16 0 . 16 1 . 05 1 . 05 γ j ) γ j ) Zj / d σ LO Zj / d σ LO EW corrections 1 1 (d σ Zj / d σ γ j ) / (d σ LO (d σ Zj / d σ γ j ) / (d σ LO 0 . 95 0 . 95 ‣ sizeable difference in EW corrections results in 
 10-15% corrections at several hundred GeV 0 . 9 0 . 9 ‣ ~5% difference between NLO QCD+EW 
 0 . 85 0 . 85 and NLO QCDxEW 0 . 8 0 . 8 0 . 75 0 . 75 250 250 500 500 750 750 1000 1000 1250 1250 1500 1500 p T , Z / γ [GeV] p T , Z / γ [GeV] High-precision predictions for V+jet production Jonas M. Lindert 8

Prelude: compare against Z/ γ -data [JHEP10(2015)128] Z / γ ratio for events with n jets ≥ 1 0 . 05 S herpa +O pen L oops T / d σ /d p γ T 0 . 04 d σ /d p Z 0 . 03 CMS data 0 . 02 JHEP 10 ( 2015 ) 128 NLO QCD 0 . 01 NLO QCD+EW 0 1 . 2 1 . 1 MC/Data 1 . 0 0 . 9 [Ciulli, Kallweit, JML, Pozzorini, Schönherr 
 for LH’15 ] 0 . 8 100 200 300 400 500 600 700 800 p Z / γ [ GeV ] T ‣ remarkable agreement with data at @ NLO QCD+EW! High-precision predictions for V+jet production Jonas M. Lindert 9

1. pure QCD uncertainties

QCD effects O d QCD = d LO QCD + d NLO QCD + d d x � ( V ) d x � ( V ) d x � ( V ) d x � ( V ) NNLO QCD . pp → Z ( → ℓ + ℓ − )+ jet @ 13 TeV 0 1 10 1 d σ /d p T , V [pb/GeV] µ 0 = 1 q X p 2 T , ` + ` − + m 2 | p T , i | ` + ` − + 1 @ A 2 i ∈ { q,g, � } 10 − 1 10 − 2 10 − 3 this is a ‘good’ scale for V+jets 10 − 4 • at large pTV: HT’/2 ≈ pTV 10 − 5 • modest higher-order corrections LO 10 − 6 • sufficient convergence NLO QCD 10 − 7 NNLO QCD 10 − 8 10 − 9 scale uncertainties due to 7-pt variations 10 − 10 1 . 2 µ R , F = ξ R , F µ 0 d σ /d σ NLO QCD 1 (0 . 5 , 0 . 5) , ariations ( ξ R , ξ F ) = (2 , 2) , (2 , 1) , (1 , 2) , (1 , 1) , (1 , 0 . 5) , (0 . 5 , 1) , variation our M P predictions are assessed by applying the scale 0 . 8 yields 
 O(20%) uncertainties at LO 
 0 . 6 O(10%) uncertainties at NLO 
 δ ( 1 ) K N k LO 0 . 4 O(5%) uncertainties at NNLO 10 2 10 3 p T , V [GeV] with minor shape variations [A. Huss, A. Gehrmann-De Ridder, 
 NNLO from T. Gehrmann, N. Glove, T.A. Morgan] High-precision predictions for V+jet production Jonas M. Lindert 11

Correlation of scale variations pp → e + e − j vs. pp → e − ¯ ν j @ 13 TeV ν ) +jet 0 . 9 consider Z+jet / W+jet p T,V -ratio @ LO Z+jet/W+jet LO (uncorrelated errors) Z( → ℓ + ℓ − )+jet / W( → e − ¯ 0 . 8 uncorrelated treatment yields 
 0 . 7 O(40%) uncertainties 0 . 6 0 . 5 0 . 4 0 . 3 0 . 2 0 . 1 0 1 . 8 1 . 6 1 . 4 d σ /d σ LO 1 . 2 1 0 . 8 0 . 6 0 . 4 0 . 2 10 2 10 3 p T , V [GeV] High-precision predictions for V+jet production Jonas M. Lindert 12