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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

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INSTITUTE FOR THEORETICAL PHYSICS

Precision Multiboson Phenomenology: Status and Prospects

Michael Rauch | SM@LHC 2015, Apr 2015

www.kit.edu

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

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Outline

Vector-Boson Fusion (Vjj) / Vector-Boson Scattering (VVjj) Triboson Production (VVV)

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 2/21

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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,

  • pposite sign as QCD for MH ∼ 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 q2

  • f intermediate vector bosons
  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 3/21

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Diboson-VBF production

[Bozzi, J¨ ager, Oleari, Zeppenfeld (VV); Campanario, Kaiser, Zeppenfeld (W±γ)] [Denner, Hosekova, Kallweit (W+W+)]

Part of the NLO wish list

[Les Houches 2005]

background to Higgs searches access to triple and quartic gauge couplings Available tools: VBFNLO

[Zeppenfeld, MR et al.]

NLO QCD, VBF approximation Phantom

[Ballestrero et al.]

LO, pp → 6f automated tools, e.g. GoSam

[Cullen et al.]

MadGraph5 aMC@NLO

[Artoisenet et al.]

u c u c νµ µ- e+ νe W+ W- γ,Z (a) νµ µ- e+ νe u c u c γ,Z γ,Z ΓV

α

(b) νµ µ- e+ νe u c u c W+ W- W (c) νµ µ- e+ νe u c u c γ,Z γ,Z TVV

αβ

(d) νµ µ- e+ νe u c u c W+ γ,Z W- TW+V

αβ

(e) e+ νe νµ µ- u c u c W- γ,Z W+ TW

αβ V

  • (f)
  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 4/21

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Scale dependence

Dependence on factorization and renormalization scale

[Bozzi, J¨ ager, Oleari, Zeppenfeld]

pp → W +W −jj pp → W +Zjj sizable scale dependence at LO: ∼ ± 10% strongly reduced at NLO: ∼ ± 2% (up to 6% in distributions) K-factor around 0.98 for µ = mV , 1.04 for µ = Q (momentum transfer)

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 5/21

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Distributions

Differential distributions: pT (j) (W+ W−)

[J¨ ager, Oleari, Zeppenfeld]

pT of the leading tagging jet pT of the second tagging jet K factor not constant over range of distribution → shape of distributions changes → simple rescaling with K factor not sufficient

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 6/21

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Distributions

Differential distributions: mjj (W+ W+)

[J¨ ager, Oleari, Zeppenfeld]

→ scale choice µ0 = Q leads to flatter differential K factor

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 7/21

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QCD-Diboson production

Most important background: QCD-Diboson Production All combinations available at NLO QCD:

[Melia, Melnikov, R¨

  • ntsch, Zanderighi; Greiner, Heinrich, Mastrolia, Ossola, Reiter, Tramontano]

[Campanario, Kerner, Ninh, Zeppenfeld; Gehrmann, Greiner, Heinrich]

W+W−jj + diagrams where quark line without attached vector bosons is replaced by gluons W+W−jj & W+W+jj (latter after changing quark flavors appropriately)

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 8/21

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QCD-Diboson production

pp → e+νeµ+νµ

[Campanario, Kerner, Ninh, Zeppenfeld]

Impact of NLO QCD corrections

[ fb/TeV ]

jj

/dm σ d

  • 2

10

  • 1

10 1 10 = 14TeV s LO NLO /2 ’ µ ’ µ ’ µ 2

jj+X

µ

ν

+

µ

e

ν

+

e → pp

K 1 1.5 2 [ TeV ]

jj

m 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 ) ’ µ ( σ ) µ ( σ 1 2

K factors typically between 1 and 1.5 corrections < 20% for invariant mass of two leading jets > 200 GeV huge correction for small mjj due to new phase-space region (almost collinear quark-gluon splitting) good scale choice (interpolates between different regions): µ′

0 = 1

2

jets

pT,i exp |yi − y12| +

  • W
  • p2

T,i + m2 W,i

  • (y12 = (y1 + y2)/2)
  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 9/21

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QCD-EW interference

pp → e+νeµ+νµ

[Campanario, Kerner, Ninh, Zeppenfeld]

Comparing contributions at LO

[fb]

tags

y ∆ /d σ d 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 14TeV, Inc, LO full EW+QCD EW VBF QCD Int

jj+X

µ

ν

+

µ

e

ν

+

e → pp

tags

y ∆ 1 2 3 4 5 6 7 [%] δ 20 40 60 80 100

EW: full O(α6) calculation VBF: VBF approximation (only t-/u-channel diagrams) QCD and EW contributions of similar size (destructive interference for QCD, no gluon-initiated contributions) QCD-EW interference largest for large pT,j, small ∆ytags up to 20% reducing to 10% (3%) for loose (tight) VBF cuts VBF contribution by far dominant in VBF region (96%) → good approximation Definition of VBF region: mjj > 500 GeV ∆ytags > 4 yj1 × yj2 < 0

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 10/21

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Matching with parton shower

NLO calculation normalization correct to NLO additional jet at high-pT accurately described theoretical uncertainty reduced low-pT jet emission badly modeled parton level description LO + parton shower LO normalization only further high-pT jets badly described Sudakov suppression at small pT events at hadron level possible ⇒ 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]

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 11/21

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Matching with parton shower

W + via VBF (similar results for W − and Z)

[Schissler, Zeppenfeld]

pT,j > 30 (tag), 20 GeV, R = 0.5, mtag

jj

> 600 GeV, ytag

j,min − 0.2 < yℓ < ytag j,max + 0.2

Relative position of third jet with respect to the two tagging jets: y⋆ = yj3 −

yj1 +yj2 2

Comparison of three different showers: Pythia, Herwig++-Default, Herwig++-Dipole low-pT 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

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 12/21

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Matching with parton shower

W + via VBF

[Schissler, Zeppenfeld]

Relative position of third jet with respect to the two tagging jets: y⋆ = yj3 −

yj1 +yj2 2

Typical |ytag

j

| ≃ 2.7 → |y⋆| < 2.7 corresponds to rapidity gap Pythia: more radiation inside rapidity gap than NLO ↔ Herwig++ (both showers): less even more pronounced when lowering pT,j3 cut to 10 GeV

  • rigin: 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

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 13/21

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Triboson production

e.g. pp → W +Zγ → ℓ+

1 ν1 ℓ+ 2 ℓ− 2 γ q ¯ q′ Z/γ∗ µ+ µ− γ e+ νe W + q ¯ q′ Z/γ∗ W + µ+ µ− γ e+ νe W + q ¯ q′ W + γ e+ νe W + Z/γ∗ µ+ µ−

background to new-physics searches → signature: multilepton + possibly missing ET gives access to triple and quartic gauge couplings (e.g. WWWW, WWγγ) processes with all bosons massive contain intermediate Higgs → background to VH, H → VV

q ¯ q′ Z/γ∗ W + µ+ µ− γ e+ νe W +

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 14/21

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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, ZZγ

[Bozzi, Campanario, Hankele, Zeppenfeld]

W ±Zγ

[Bozzi, Campanario, MR, Rzehak, Zeppenfeld]

W ±γγ production (no leptonic decays, including CKM and fragmentation)

[Baur, Wackeroth, Weber]

W ±γγ

[Bozzi, Campanario, MR, Zeppenfeld]

Zγγ, 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

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 15/21

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W ±Zγ distributions

Scale dependence

[Bozzi, Campanario, MR, Rzehak, Zeppenfeld]

W +Zγ (µ0 = mWZγ)

0.5 1 1.5 2 2.5 3 3.5 0.1 1 10 σ [fb] ξ solid: µF = µR = ξ µ0 dashed: µF = ξ µ0 , µR = µ0 dotted: µF = µ0 , µR = ξ µ0 LO NLO

Individual contributions W −Zγ

0.5 1 1.5 2 2.5 0.1 1 10 σ [fb] ξ Total NLO Virtual-born Virtual-box Virtual-pentagons Real

Transverse momentum of the photon Total cross section NLO/LO

0.0001 0.001 0.01 0.1 150 100 50 50 100 150 dσ/dpTγ [fb] pTγ [GeV] W-Zγ W+Zγ

Differential K-factor without/with jet veto

0.5 1 1.5 2 2.5 3 3.5 150 100 50 50 100 150 K-factor pTγ [GeV] W-Zγ W+Zγ

⇒ Sizable K-factor ∼ 1.9, strongly dependent on phase-space region ⇒ Fully differential NLO Monte Carlo necessary

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 16/21

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Wγγ

Radiation Zero in Wγγ at LO SM amplitude for q ¯ Q → W ±γ(γ) vanishes for cos θ∗

W = ± 1 3

(for W ±γγ photons must be collinear)

[Baur, Han, Kauer, Sobey, Zeppenfeld]

Negative interference between

W γ

and

W γ

LHC symmetric ⇒ radiation dip at 0 spoiled by

final-state radiation (photon emission off final-state lepton) gluon-initiated processes (NLO real emission contribution)

look at rapidity difference yγγ − yW for cos θγγ > 0 and cos θγγ < 0 final-state radiation suppressed by cut MT,ℓν > 70 GeV

0.05 0.1 0.15

  • 4
  • 3
  • 2
  • 1

1 2 3 4 d σ/d yγγ-yW+ [fb] yγγ-yW+ W+γγ LO cosθ>0 cosθ<0 0.5 1 1.5

  • 4
  • 3
  • 2
  • 1

1 2 3 4 d σ/d yγγ-yW+ [fb] yγγ-yW+ W+γγ NLO cosθ>0 cosθ<0

0.1 0.2 0.3 0.4

  • 5
  • 4
  • 3
  • 2
  • 1

1 2 3 4 5 d σ/d yγγ-yW+ [fb] yγγ-yW+ W+γγ NLO cosθ>0 cosθ<0

pT,j < 50 GeV

⇒ radiation zero not present at NLO, not restored by jet veto

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 17/21

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Wγγ + jet

Large K factors in W ±γγ calculation ⇒ need higher orders in perturbation theory NLO calculation of real emission part important ingredient for NNLO precision ⇒ W ±γγ + jet calculation at NLO QCD

[Campanario, Englert, MR, Zeppenfeld]

First triboson + jet process at NLO QCD Leptonic decays of W ± and all off-shell effects included Scale dependence of W +γγj

2 4 6 8 10 12 14 16 0.1 1 10 σ [fb] ξ ℓ+νγγ j @ LHC solid: µF= µR= ξ mWγγ dashed: µF= ξ mWγγ, µR= mWγγ dotted: µR= ξ mWγγ, µF= mWγγ LO NLO

σLO = 2 · 4.6398(1) fb σNLO = 2 · 6.5026(8) fb K = 1.40

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 18/21

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SLIDE 19

Distributions

Differential max pj

T distribution K(max pj

T )

max pj

T [GeV]

700 600 500 400 300 200 100

1.6 1.2 0.8 0.4

NLO (veto) veto uncertainty NLO LO dσ/d max pj

T [fb GeV−1]

W +γγj @ LHC µR = µF = mW γγ max pj

T [GeV]

700 600 500 400 300 200 100

0.1 0.01 0.001

Invariant Wγγ mass

K(mW γγ) mW γγ [GeV] 900 750 600 450 300 150

1.6 1.5 1.4 1.3 1.2 1.1 1

NLO (veto) veto uncertainty NLO LO dσ/d mW γγ [fb GeV−1] W +γγj @ LHC µR = µF = mW γγ mW γγ [GeV] 900 750 600 450 300 150

0.1 0.01 0.001

⇒ results consistent with NLO QCD corrections for VVj ⇒ global K factor not a good approximation → need full NLO calculation ⇒ large scale variation uncertainties for exclusive sample pT,j2 < 50 GeV

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 19/21

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SLIDE 20

Triboson + Parton Shower

Study of pp → 3ℓ+/ ET with VH, H → VV,ττ as signal

[Sherpa+OpenLoops (H¨

  • che et al.)]

Triboson processes appearing as background, simulated up to merging of VVV, VVVj at NLO QCD and VVVjj at LO, plus parton shower → non-trivial application of multi-jet merging at NLO

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 20/21

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Conclusions

Multi-boson production important processes for LHC: access to triple/quartic gauge couplings background to Higgs searches Vector-Boson Fusion/Scattering: modest NLO QCD corrections, small remaining scale uncertainties state-of-the-art: NLO QCD + parton shower enhance over irred. QCD background by VBF cuts ↔ significant discrepancies in predicting central jet activity → needs further studies Triboson production: large NLO QCD K factors due to new channels → merging with higher jet multiplicities fixed jet vetoes can induce large theory uncertainties

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 21/21

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Experimental cuts for Wγγ

Experimental values used: pT

j > 20 GeV

|ηparton| < 5.0 |ηj| < 4.5 pT

l > 20 GeV

|ηl| < 2.5 pT

γ > 20 GeV

|ηγ| < 2.5 ∆Rlγ > 0.4 ∆Rγγ > 0.4 ∆Rjγ > 0.4 ∆Rpγ,Frixione = 0.7 Eff.Frixione = 1.0 mW = 80.398 GeV mZ = 91.1876 GeV PDFs : LO : CTEQ6l1 NLO : CT10 LHC : √ S = 14 TeV

  • M. Rauch – Precision Multiboson Phenomenology: Status and Prospects

SM@LHC 2015, Apr 2015 22/21