Multi-boson Production in Weak Boson Fusion Michael Rauch | DIS 2014, - - PowerPoint PPT Presentation

▶
multi boson production in weak boson fusion
SMART_READER_LITE
LIVE PREVIEW

Multi-boson Production in Weak Boson Fusion Michael Rauch | DIS 2014, - - PowerPoint PPT Presentation

Feb 17, 2024 180 likes •355 views

Multi-boson Production in Weak Boson Fusion Michael Rauch | DIS 2014, Apr 2014 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 VBF

slide-1
SLIDE 1

INSTITUTE FOR THEORETICAL PHYSICS

Multi-boson Production in Weak Boson Fusion

Michael Rauch | DIS 2014, Apr 2014

www.kit.edu

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

slide-2
SLIDE 2

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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 2/16

slide-3
SLIDE 3

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 anomalous triple and quartic gauge couplings

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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 3/16

slide-4
SLIDE 4

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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 4/16

slide-5
SLIDE 5

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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 5/16

slide-6
SLIDE 6

Distributions

Differential distributions: mjj (W+ W+)

[J¨ ager, Oleari, Zeppenfeld]

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

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 6/16

slide-7
SLIDE 7

QCD-Diboson production

Calculations at NLO QCD: W± W± jj, W+ W− jj, W± Z jj, W± γ jj, γ γ jj

[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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 7/16

slide-8
SLIDE 8

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

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 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 – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 8/16

slide-9
SLIDE 9

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

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 9/16

slide-10
SLIDE 10

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 POWHEG-BOX

[Alioli, Hamilton, Nason, Oleari, Re]

implementation of W +W −, W ±W ± and ZZ via VBF available

[J¨ ager, Zanderighi]

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 10/16

slide-11
SLIDE 11

Matching with parton shower

W +W − via VBF

[J¨ ager, Zanderighi]

Relative position of third jet with respect to the two tagging jets: y⋆ = yj3 − yj1 + yj2 2

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

  • 4
  • 3
  • 2
  • 1

1 2 3 4 dσ/d y* [fb] y* pt,j3 > 10 GeV POWHEG+PYTHIA NLO 0.005 0.01 0.015 0.02 0.025 0.03

  • 4
  • 3
  • 2
  • 1

1 2 3 4 dσ/d y* [fb] y* pt,j3 > 25 GeV POWHEG+PYTHIA NLO

Extra jet activity in central region predicted by parton-shower calculation Relevant differences to pure NLO calculation

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 11/16

slide-12
SLIDE 12

Unitarization of WW-scattering

Test of electro-weak symmetry breaking Longitudinal WW scattering contains Higgs graphs:

+ + + +

necessary for correct high-energy behaviour (otherwise unitarity violation at ∼ 1 TeV) MH ∼

s v2

Signal amplitude for s-, t- and u-channel exchange of H MB ∼ −s

v2

continuum electroweak background amplitude

1e-10 1e-09 1e-08 1e-07 1e-06 1e-05 0.0001 0.001 0.01 0.1 500 1000 1500 2000 2500 3000 3500 4000 dσ/dmWW [fb/GeV] mWW [GeV] SM-H (126 GeV) H (126 GeV), κ2

V=0.7

no H

exact cancellation only for SM couplings (Higgs part may be split

  • ver different bosons with
  • i g2

hi VV = g2 HVV,SM, e.g. 2HDM)

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 12/16

slide-13
SLIDE 13

Anomalous quartic gauge couplings

New physics at high scale Λ could influence gauge couplings ⇒ anomalous gauge couplings

[Eboli et al. ; recent review: Wackeroth (ed.), Degrande, MR et al. ]

Different approaches to parametrize effects → Effective field theory LEFT =

  • d
  • i

f (d)

i

Λd−4 O(d)

i

Operators O with low energy degrees of freedom respect gauge symmetries Dimension-8 operators in Lagrangian (Φ Higgs doublet, W µν/Bµν: SU(2)/U(1) field strength tensors):

e.g. LM,2 ∝

  • BµνBµν
  • ×
  • DβΦ

† DβΦ

  • ,

LT,1 ∝

  • W ανWµβ
  • ×
  • W µβWαν
  • , . . .

(at least) four gauge fields in each term → modify quartic gauge couplings triple gauge couplings contribute as well in general unitarity violation at high energies → avoid region or apply unitarization method (K-matrix, formfactor, . . . )

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 13/16

slide-14
SLIDE 14

Anomalous quartic gauge couplings

[Schlimpert, Zeppenfeld]

Normalized / pt distribution

1 2 3 4 5 6 7 8 200 400 600 800 1000 1/σ dσ/d/ pT

  • 10−3GeV −1

/ pT [GeV]

Standard Model fM2/Λ4 = 800 TeV−4 fT1/Λ4 = 25 TeV−4 fWWW /Λ2 = 10 TeV−2

Normalized |η|max

ℓ

distribution

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.5 1 1.5 2 2.5 1/σ dσ/d|η|max

ℓ

|η|max

ℓ

Standard Model fM2/Λ4 = 800 TeV−4 fT1/Λ4 = 25 TeV−4 fWWW /Λ2 = 10 TeV−2

Anomalous couplings enhance predominantly high-energy region ∆σ ∼ O(1 − 4%) for total cross section, ∆σ ∼ O(20 − 100%) in high-energy region, mT

WW > 800 GeV

Visible changes in distributions, different for individual couplings → distinguish between different couplings

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 14/16

slide-15
SLIDE 15

Experimental Results

[ATLAS-CONF-2014-013]

Recently first evidence (3.6σ) for W ±W ± via VBF by ATLAS (W → eνe, µνµ) (4.5 σ for W ±W ±jj production total (QCD+EW))

Events/50 GeV

  • 1

10 1 10

2

10 Data 2012

  • Syst. Uncertainty

jj Electroweak

±

W

±

W jj Strong

±

W

±

W Prompt Conversions Other non-prompt ATLAS Preliminary = 8 TeV s ,

  • 1

20.3 fb [GeV]

jj

m 200 400 600 800 1000 1200 1400 1600 1800 2000 Data/Expected 2 Data/Expected

  • Syst. Uncertainty

4

α ›0.4 ›0.3 ›0.2 ›0.1 0.1 0.2 0.3 0.4

5

α ›0.6 ›0.4 ›0.2 0.2 0.4 0.6

ATLAS Preliminary = 8 TeV s ,

›1

20.3 fb jj

±

W

±

W → pp K›matrix unitarization 68% CL 95% CL expected 95% CL Standard Model confidence intervals

Good agreement with SM prediction ⇒ Limits on anomalous couplings σfid

exp = 1.3 ± 0.4 (stat) ± 0.2 (syst) fb

σfid

th = 0.95 ± 0.06 fb

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 15/16

slide-16
SLIDE 16

Conclusions

Di-boson production via Weak Boson Fusion important process for the LHC

Higgs searches – unitarity in WW scattering testing anomalous (triple and) quartic gauge couplings

NLO QCD corrections modest for some processes NLO QCD + parton shower available VBF approximation in VBF region justified in general also QCD and QCD-EW interference contributions first experimental evidence in W± W± jj production by ATLAS

  • M. Rauch – Multi-boson Production in Weak Boson Fusion

DIS 2014, Apr 2014 16/16