Probing soft and hard radiations with Z (+ jets) Laurent Favart, - PowerPoint PPT Presentation

REF2017, Madrid Probing soft and hard radiations with Z (+ jets) Laurent Favart, Philippe Gras, Anastasia Grebenyuk, Sandeep Kaur, Qun Wang, Fengwangdong Zhang 13 November 2017

Introduction ◮ Z (+ jets) precision measurements crucial for deep understanding and modeling of QCD interactions ◮ standard candle at LHC: high cross section; almost background free; high precision of the full kinematic reconstruction ◮ important for modeling of the production mechanism involved in the Higgs boson and new physics ◮ Z (+ jets) process can probe different aspects of QCD effects ◮ test latest higher order calculations and MC based event generators ◮ studying multiple gluon emissions and test the models with high accuracy of soft gluon resummation 2

Theoretical prediction for cross section ◮ MADGRAPH5 AMC@NLO + Pythia8 (denoted as LO MG5 a MC ) ◮ LO matrix element up to 4 partons ◮ k T -MLM merging ◮ NNPDF3.0 NLO PDF, CUETP8M1 Pythia8 tune ◮ MADGRAPH5 AMC@NLO + Pythia8 (denoted as NLO MG5 a MC ) ◮ NLO matrix element up to 2 partons (LO accuracy for 3 partons) ◮ FxFx jet merging ◮ NNPDF3.0 NLO PDF, CUETP8M1 Pythia8 tune ◮ Z+1 jet fixed order NNLO (Phys. Rev. Lett. 115, 062002) ◮ Correction for hadronization and multiple parton interaction computed with MADGRAPH5 AMC@NLO + Pythia8 ◮ CT14 PDF 3

Two models with improved soft gluon resummation treatment: ◮ Geneva 1.0-RC2 + Pythia8 (arXiv:1508.01475) ◮ NNLL’+NNLO matched to PS ◮ Use n-jettiness (PRL 105, 092002 (2010)) to separate N-jet and inclusive (N+1)-jet region, here τ 0 and τ 1 ◮ τ 0 ( ≡ beam-thrust, � particles E i − | p z , i | ) dependence resummed at NNLL’ ◮ d σ ≥ 0 j at NNLO, d σ ≥ 1 j at NLO, d σ ≥ 2 j at LO, ◮ PDF4LHC15 NNLO; α s ( m Z ) = 0 . 118 and 0 . 1135 (for ME and PS) ◮ Specific Pythia8 tune based on CUETP8M1 ◮ DYRes 1.0 (JHEP12(2015)047) (shown for p T of the Z boson for N jets ≥ 0) ◮ NNLL+NNLO fixed order calculation ◮ NNPDF 3.1 NNLO and α s ( m Z ) =0.118 4

Transverse momentum of the Z boson for N jets ≥ 0 ≤ MG5_aMC + PY8 ( 2j NLO + PS) (Z) [pb/GeV] ≤ MG5_aMC + PY8 ( 2j NLO + PS) MC study 45 ≤ MG5_aMC + PY8 ( 4j LO + PS) GE + PY8 (NNLL' +NNLO ) 40 τ 0 DYRes (NNLL + NNLO) 35 30 T /dp NLO MG5 a MC + Pythia8 25 σ d LO MG5 a MC + Pythia8 20 15 Geneva (NNLL’+NNLO) + Pythia8 with γ → Z/ * ll 10 α s ( m Z ) = 0 . 118 and 0 . 1135 (dashed line) 5 DYRes NNLL+NNLO 1.4 MG5_aMC Prediction The ratio is taken with respect to NLO 1.2 1 MG5 a MC 0.8 0.6 ⊕ ⊕ ⊕ α Stat. theo. PDF unc. s Theoretical uncertainties are included for 1.4 MG5_aMC Prediction 1.2 NLO MG5 a MC and Geneva 1 0.8 0.6 Stat. unc. 1.4 High p T : MG5_aMC Prediction 1.2 1 ◮ predictions with beyond LO ME 0.8 α ⊕ ⊕ agrees with each other 0.6 Stat. Stat. theo. unc. theo. unc. = 0.1135 s 1.4 ◮ LO MG5 a MC is below NLO Prediction MG5_aMC 1.2 1 MG5 a MC 0.8 0.6 Stat. unc. 2 3 10 10 10 p (Z) [GeV] 5 T

Transverse momentum of the Z boson for N jets ≥ 0 Small p T : ≤ MG5_aMC + PY8 ( 2j NLO + PS) (Z) [pb/GeV] ≤ ◮ both MG5 a MC are based of Pythia8 CUETP8M1 MG5_aMC + PY8 ( 2j NLO + PS) MC study 45 ≤ MG5_aMC + PY8 ( 4j LO + PS) ◮ all the predictions except Geneva are similar 40 GE + PY8 (NNLL' +NNLO ) τ 0 DYRes (NNLL + NNLO) 35 30 T /dp 25 σ d Parameters Geneva tune 20 CUETP8M1 MultipartonInteractions:pT0Ref 2.4024 2.27 15 γ → Z/ * ll MultipartonInteractions:ecmPow 0.25208 0.25208 10 MultipartonInteractions:expPow 1.6 1.6 5 MultipartonInteractions:alphaSvalue 0.130 0.118 (0.1135) 1.4 ColourReconnection:range 1.8 1.55 Prediction MG5_aMC 1.2 SpaceShower:pT0Ref 2.0 1.22 1 SpaceShower:alphaSvalue 0.1365 0.118 (0.1135) 0.8 ⊕ ⊕ ⊕ α 0.6 Stat. theo. PDF unc. TimeShower:alphaSvalue 0.1365 0.118 (0.1135) s 1.4 BeamRemnants:primordialKThard 1.8 0.32 Prediction MG5_aMC 1.2 1 0.8 0.6 Stat. unc. Primordial k T is reduced in Geneva − → less phase space 1.4 MG5_aMC Prediction 1.2 for parton shower and more from the first principle 1 0.8 α 0.6 Stat. Stat. ⊕ ⊕ theo. unc. theo. unc. = 0.1135 s ◮ Geneva : lower value 0.1135 for α s ( m Z ) shows better 1.4 MG5_aMC Prediction 1.2 agreement with NLO MG5 a MC 1 0.8 ◮ Geneva : no systematic attempt made to tune the 0.6 Stat. unc. 2 3 10 10 10 parton shower. Impact of the parton shower tuning p (Z) [GeV] T need to be understood. 6

Jets ◮ By requiring a jet one sensitive to hard gluon radiation in the central region ◮ Possibly to test higher order calculations at high transverse momentum ≤ MG5_aMC + PY8 ( 2j NLO + PS) [pb] MC study ≤ MG5_aMC + PY8 ( 2j NLO + PS) 3 10 ≤ MG5_aMC + PY8 ( 4j LO + PS) jets /dN GE + PY8 (NNLL' +NNLO ) 2 τ 0 10 σ d ◮ Jet selection: p T > 30 GeV, | y | < 2 . 4 , 10 separation from the dressed lepton of 1 ∆ R > 0 . 4 − 1 10 anti-k (R = 0.4) Jets T jet jet ◮ LO MG5 a MC and NLO MG5 a MC show p > 30 GeV, |y | < 2.4 − 2 10 T γ → Z/ * ll slightly different distribution: more high jet 1.4 Prediction MG5_aMC 1.2 event for NLO MG5 a MC 1 0.8 ◮ In Geneva third jet is described by PS . No ⊕ ⊕ ⊕ α 0.6 Stat. theo. PDF unc. s 1.4 MG5_aMC systematic attempt made to tune the parton Prediction 1.2 1 shower → disagreements in the central value 0.8 0.6 Stat. unc. with the data are expected for N jets ≥ 3 1.4 MG5_aMC Prediction 1.2 1 0.8 α 0.6 Stat. Stat. ⊕ ⊕ theo. unc. theo. unc. = 0.1135 s = 0 = 1 = 2 = 3 = 4 = 5 = 6 7 N jets

Jet kinematics Leading jet p T : Subleading jet p T : ≤ MG5_aMC + PY8 ( 2j NLO + PS) ) [pb/GeV] MG5_aMC + PY8 ( ≤ 2j NLO + PS) MC study 10 ≤ MG5_aMC + PY8 ( 4j LO + PS) GE + PY8 (NNLL' +NNLO ) τ 0 N NNLO (1j NNLO) jetti ≤ 1 MG5_aMC + PY8 ( 2j NLO + PS) (j 1 ) [pb/GeV] T MC study ≤ MG5_aMC + PY8 ( 2j NLO + PS) /dp ≤ σ MG5_aMC + PY8 ( 4j LO + PS) d − 10 1 GE + PY8 (NNLL' +NNLO ) 1 τ 0 2 (j T anti-k (R = 0.4) Jets /dp T − 2 jet jet 10 p > 30 GeV, |y | < 2.4 T γ γ → → ≥ σ − Z/ Z/ * * ll, N ll 1 1 10 d jets 1.4 MG5_aMC Prediction 1.2 anti-k (R = 0.4) Jets 1 T jet − jet 10 2 p > 30 GeV, |y | < 2.4 0.8 T γ γ → → ≥ Z/ Z/ * * ll, N ll 2 0.6 Stat. ⊕ theo. ⊕ PDF ⊕ α unc. jets s 1.4 1.4 MG5_aMC Prediction 1.2 MG5_aMC Prediction 1.2 1 1 0.8 0.8 0.6 Stat. unc. 0.6 Stat. ⊕ theo. ⊕ PDF ⊕ α unc. s 1.4 1.4 MG5_aMC Prediction 1.2 Prediction MG5_aMC 1.2 1 1 0.8 0.8 ⊕ ⊕ α 0.6 Stat. Stat. theo. unc. theo. unc. = 0.1135 0.6 Stat. unc. s 1.4 1.4 Prediction MG5_aMC MG5_aMC 1.2 Prediction 1.2 1 1 0.8 0.8 ⊕ α 0.6 Stat. theo. unc. 0.6 Stat. Stat. ⊕ ⊕ theo. unc. theo. unc. = 0.1135 s 50 100 150 200 250 300 350 400 50 100 150 200 250 p (j ) [GeV] p (j ) [GeV] T 1 T 2 ◮ LO MG5 a MC has slightly different shape w.r.t NLO MG5 a MC ◮ Leading jet p T : Z+1 jet fixed order NNLO is similar to NLO MG5 a MC within the theory uncertainty; increase theory precision for NNLO calculation ◮ Subleading jet p T : Geneva undershoots NLO MG5 a MC at low p T 8

Jet kinematics CMS-PAS-SMP-15-010 Eur. Phys. J. C77 (2017) 361 (CMS leading jet p T in Z+jets events) (ATLAS leading jet p T in Z+jets events ) 10 2 [pb/GeV] + − γ → ≥ ATLAS Z/ *( l l ) + 1 jet 10 Data − 1 13 TeV, 3.16 fb Z + ≥ 1 jet N NNLO jetti 1 Z γ B H + S / LACK AT HERPA jet * + T ≥ S 2.2 /dp HERPA 1 j e 10 -1 t A LPGEN + P Y 6 σ Z/ γ * + MG5_aMC + P Y 8 CKKWL d ≥ 2 jets, 10 -2 MG5_aMC + P Y 8 FxFx × 10 − 1 Z/ γ -3 10 * + ≥ 3 jets, × 10 − -4 2 10 Z/ γ * + ≥ 4 jets, -5 10 × − 10 3 -6 10 anti-k jets, R = 0.4 t jet jet   10 -7 p > 30 GeV, y < 2.5 T Pred./Data 1.5 100 γ ≥ 200 300 400 500 600 700 Z/ * + 1 jet 1 0.5 Pred./Data 1.5 100 200 300 400 500 600 700 γ ≥ Z/ * + 2 jets 1 0.5 100 200 300 400 500 600 700 jet p (leading jet) [GeV] T ◮ At high p T LO ME model does not describe the measurements → NLO correction is needed ◮ NNLO ME model describes the measurements as good as NLO ME model 9

Transverse momentum of the Z boson for N jets ≥ 1 ≤ MG5_aMC + PY8 ( 2j NLO + PS) (Z) [pb/GeV] 4 MC study ≤ MG5_aMC + PY8 ( 2j NLO + PS) ≤ 3.5 MG5_aMC + PY8 ( 4j LO + PS) At least one jet requirement shift the peak GE + PY8 (NNLL' +NNLO ) τ 0 3 toward the higher value → anti-k (R = 0.4) Jets possibility of studying multiple gluon 2.5 T T jet jet /dp p > 30 GeV, |y | < 2.4 T emissions away from the non-perturbative γ γ → → ≥ Z/ Z/ * * ll, N ll 1 2 σ jets region d 1.5 1 High p T : 0.5 ◮ LO MG5 a MC is below NLO MG5 a MC 1.4 MG5_aMC Prediction 1.2 ◮ Geneva agrees with NLO MG5 a MC 1 0.8 Small p T : ⊕ ⊕ ⊕ α 0.6 Stat. theo. PDF unc. s ◮ Geneva is below NLO MG5 a MC by 1.4 MG5_aMC Prediction 1.2 20 % , the difference is more 1 pronounced than in inclusive scenario 0.8 0.6 Stat. unc. ◮ Geneva : use of the lower value 1.4 MG5_aMC Prediction 0.1135 for α s ( m Z ) improves only the 1.2 1 first bin 0.8 α ⊕ ⊕ = 0.1135 0.6 Stat. Stat. theo. unc. theo. unc. s 2 3 10 10 10 p (Z) [GeV] 10 T