Precision Multiboson Phenomenology: Status and Prospects Michael Rauch | SM@LHC 2015, Apr 2015 I NSTITUTE FOR T HEORETICAL P HYSICS KIT – University of the State of Baden-Wuerttemberg and www.kit.edu National Research Center of the Helmholtz Association
Outline Vector-Boson Fusion ( Vjj ) / Vector-Boson Scattering ( VVjj ) Triboson Production ( VVV ) SM@LHC 2015, Apr 2015 2/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
VBF event topology VBF (vector-boson fusion) topology shows distinct signature two tagging jets in forward region reduced jet activity in central region leptonic decay products typically between tagging jets → two-sided DIS First studied in context of Higgs searches [Han, Valencia, Willenbrock; Figy, Oleari, Zeppenfeld; . . . ] ∼ 10 % compared to main production mode gluon fusion NLO QCD corrections moderate ( O ( � 10 %)) NLO EW same size, opposite sign as QCD for M H ∼ 126 GeV [Ciccolini et al. , Figy et al. ] NNLO QCD known for subsets: no significant contributions [Harlander et al. , Bolzoni et al. ] advantageous scale choice: momentum transfer q 2 of intermediate vector bosons SM@LHC 2015, Apr 2015 3/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Diboson-VBF production ager, Oleari, Zeppenfeld (VV); Campanario, Kaiser, Zeppenfeld (W ± γ )] [Bozzi, J¨ [Denner, Hosekova, Kallweit (W + W + )] e + µ - ν e α Γ V ν e Part of the NLO wish list e + γ ,Z ν µ ν µ W + W - µ - [Les Houches 2005] u u u u γ ,Z γ ,Z background to Higgs searches c c c c access to triple and quartic gauge (a) (b) couplings µ - u u W - γ ,Z ν µ e + Available tools: u u αβ ν e W T VV ν µ VBFNLO c c [Zeppenfeld, MR et al.] ν e µ - γ ,Z W + NLO QCD, VBF approximation e + c c (c) (d) Phantom [Ballestrero et al.] LO, pp → 6 f µ - ν e W - W + e + ν µ automated tools, e.g. u u u u W + W - µ - ν e GoSam [Cullen et al.] αβ αβ T W + V T W - V e + ν µ MadGraph5 aMC@NLO γ ,Z γ ,Z c c c c [Artoisenet et al.] (e) (f) SM@LHC 2015, Apr 2015 4/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Scale dependence Dependence on factorization and renormalization scale [Bozzi, J¨ ager, Oleari, Zeppenfeld] pp → W + Zjj pp → W + W − jj sizable scale dependence at LO: ∼ ± 10% strongly reduced at NLO: ∼ ± 2% (up to 6% in distributions) K-factor around 0.98 for µ = m V , 1.04 for µ = Q (momentum transfer) SM@LHC 2015, Apr 2015 5/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Distributions Differential distributions: p T ( j ) (W + W − ) [J¨ ager, Oleari, Zeppenfeld] p T of the leading tagging jet K factor not constant over range of distribution → shape of distributions changes → simple rescaling with K factor not sufficient p T of the second tagging jet SM@LHC 2015, Apr 2015 6/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Distributions Differential distributions: m jj (W + W + ) [J¨ ager, Oleari, Zeppenfeld] → scale choice µ 0 = Q leads to flatter differential K factor SM@LHC 2015, Apr 2015 7/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
QCD-Diboson production Most important background: QCD-Diboson Production All combinations available at NLO QCD: [Melia, Melnikov, R¨ ontsch, Zanderighi; Greiner, Heinrich, Mastrolia, Ossola, Reiter, Tramontano] [Campanario, Kerner, Ninh, Zeppenfeld; Gehrmann, Greiner, Heinrich] W + W − jj W + W − jj & W + W + jj (latter after changing quark flavors appropriately) + diagrams where quark line without attached vector bosons is replaced by gluons SM@LHC 2015, Apr 2015 8/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
QCD-Diboson production pp → e + ν e µ + ν µ [Campanario, Kerner, Ninh, Zeppenfeld] Impact of NLO QCD corrections K factors typically between 1 and 1.5 + + pp e jj+X → ν µ ν 10 e µ corrections < 20 % for s = 14TeV invariant mass of two leading jets LO [ fb/TeV ] NLO > 200 GeV ’ /2 µ 1 0 ’ µ huge correction for small m jj due 0 jj 2 ’ µ /dm 0 to new phase-space region σ d (almost collinear quark-gluon -1 10 splitting) good scale choice (interpolates -2 10 between different regions): 2 1.5 K 0 = 1 � � 1 µ ′ p T , i exp | y i − y 12 | 2 jets ) 2 ) 0 µ ’ µ ( σ ( σ 1 � � � p 2 T , i + m 2 + W , i 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 m [ TeV ] W jj ( y 12 = ( y 1 + y 2 ) / 2) SM@LHC 2015, Apr 2015 9/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
QCD-EW interference pp → e + ν e µ + ν µ [Campanario, Kerner, Ninh, Zeppenfeld] Comparing contributions at LO QCD and EW contributions of 1.6 similar size + + pp → e ν µ ν jj+X e µ 1.4 (destructive interference for QCD, 14TeV, Inc, LO full 1.2 no gluon-initiated contributions) EW+QCD EW 1 VBF QCD-EW interference largest for [fb] QCD tags 0.8 Int large p T , j , small ∆ y tags y ∆ /d 0.6 up to 20% reducing to 10% (3%) σ d for loose (tight) VBF cuts 0.4 0.2 VBF contribution by far dominant in VBF region (96%) 0 100 → good approximation 80 [%] 60 40 δ 20 0 0 1 2 3 4 5 6 7 Definition of VBF region: ∆ y tags m jj > 500 GeV EW: full O ( α 6 ) calculation ∆ y tags > 4 VBF: VBF approximation (only t-/u-channel diagrams) y j 1 × y j 2 < 0 SM@LHC 2015, Apr 2015 10/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Matching with parton shower NLO calculation LO + parton shower normalization correct to NLO LO normalization only additional jet at high- p T further high- p T jets badly accurately described described theoretical uncertainty reduced Sudakov suppression at small p T low- p T jet emission badly events at hadron level possible modeled parton level description ⇒ combine both approaches → NLO + parton shower POWHEG-BOX [Alioli, Hamilton, Nason, Oleari, Re] currently available VBF implementations: Z [J¨ ager, Schneider, Zanderighi] W ± , Z [Schissler, Zeppenfeld] W ± W ± , W ± W ∓ [J¨ ager, Zanderighi] ZZ [J¨ ager, Karlberg, Zanderighi] SM@LHC 2015, Apr 2015 11/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Matching with parton shower W + via VBF (similar results for W − and Z ) [Schissler, Zeppenfeld] p T , j > 30 (tag), 20 GeV, R = 0 . 5, m tag > 600 GeV, y tag j , min − 0 . 2 < y ℓ < y tag j , max + 0 . 2 jj y j 1 + y j 2 Relative position of third jet with respect to the two tagging jets: y ⋆ = y j 3 − 2 Comparison of three different showers: Pythia, Herwig++-Default, Herwig++-Dipole low- p T region: damping due to Sudakov factor hard 3rd jet � 75 GeV: lower rates than NLO from additional hard/wide-angle radiation y ⋆ : relevant differences between shower algorithms SM@LHC 2015, Apr 2015 12/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Matching with parton shower W + via VBF [Schissler, Zeppenfeld] y j 1 + y j 2 Relative position of third jet with respect to the two tagging jets: y ⋆ = y j 3 − 2 Typical | y tag | ≃ 2 . 7 → | y ⋆ | < 2 . 7 corresponds to rapidity gap j Pythia: more radiation inside rapidity gap than NLO ↔ Herwig++ (both showers): less even more pronounced when lowering p T , j 3 cut to 10 GeV origin: more soft partons predicted by Pythia, mostly collinear radiation by Herwig++ Even bigger differences for additional jets generated solely by parton shower → Uncertainty of prediction SM@LHC 2015, Apr 2015 13/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Triboson production e.g. pp → W + Z γ → ℓ + 1 ν 1 ℓ + 2 ℓ − 2 γ q ν e q γ q W + W + Z/γ ∗ µ − e + ν e µ + W + γ e + Z/γ ∗ µ − Z/γ ∗ µ − W + γ µ + µ + ν e q ′ q ′ q ′ ¯ ¯ ¯ W + e + ν e background to new-physics searches W + q e + → signature: multilepton W + γ + possibly missing E T gives access to triple and quartic gauge µ − q ′ ¯ Z/γ ∗ couplings (e.g. WWWW , WW γγ ) µ + processes with all bosons massive contain intermediate Higgs → background to VH , H → VV SM@LHC 2015, Apr 2015 14/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
Triboson production All combinations V ∈{ W ± , Z , γ } at NLO QCD discussed in literature: ZZZ production (no leptonic decays, no Higgs contribution) [Lazopoulos, Melnikov, Petriello] W + W − Z production [Hankele, Zeppenfeld] ZZZ , W + W − Z , ZZW ± , W ± W ∓ W ± (no leptonic decays, no Higgs contributions) [Binoth, Ossola, Papadopoulos, Pittau] ZZW ± , W ± W ∓ W ± [Campanario, Hankele, Oleari, Prestel, Zeppenfeld] ZZZ W + W − γ , ZZ γ [Bozzi, Campanario, Hankele, Zeppenfeld] W ± Z γ [Bozzi, Campanario, MR, Rzehak, Zeppenfeld] W ± γγ production (no leptonic decays, including CKM and fragmentation) [Baur, Wackeroth, Weber] W ± γγ [Bozzi, Campanario, MR, Zeppenfeld] Z γγ , γγγ [Bozzi, Campanario, MR, Zeppenfeld] W + W − Z (no leptonic decays, NLO QCD+EW) [Nhung, Ninh, Weber] VBFNLO approximations: [Zeppenfeld, MR, et al.] fermion mass effects neglected, CKM matrix effects neglected Interference terms due to identical particles in the final state neglected SM@LHC 2015, Apr 2015 15/21 M. Rauch – Precision Multiboson Phenomenology: Status and Prospects
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