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Trilinear γ WW Couplings at a γγ – collider at ILC. K.M önig, J.Sekaric DESY-Zeuthen. Introduction. Dominating diagram for γγ  W + W - Two initial states. Ambiguities in 4-jet events: ( cos θ 1,2 , φ 1,2 ) ↔ (- cos θ 1,2 , φ 1,2 + π ). q. . y. W BACKWARD.  1. x.  2. x.  1.

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Trilinear γ WW Couplings at a γγ – collider at ILC

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Trilinear

γWW Couplings at a

γγ– collider at ILC

K.Mönig, J.Sekaric

DESY-Zeuthen


Introduction

Dominating diagram for γγ W+W-

Two initial states

Ambiguities in 4-jet events:

(cosθ1,2,φ1,2) ↔ (-cosθ1,2,φ1,2+π)

q

y

WBACKWARD

1

x

2

x

1

z

2

z

y

WFORWARD

q


Total Cross-Section vs. CMS

notation

Denner, Dittmaier, Schuster, hep-ph/9503442


Total Cross-Section (κγ, λγ) - Whizard

On-shell Ws at cme = 400 GeV, 100% polarized beams


Diff. Cross-Section (κγ, λγ) - Whizard

Relative deviations of diff. cross-section from the SM in presence of anomalous couplings

WLWL masked

by dominating

WTWT fraction


Analysis

  • Signal (γγ→WW) and (background, pile-up) samples at detector level WHIZARD – W. Kilian & CIRCE2 – T. Ohl (Telnov’s spectra) (variable energy spectra, 85% polarized e- and 100% γbeams)

    -pileup : low-energy γγ qq (1.8 ev/BX)

    -background :γγ qq  4 jets (O’Mega)

    JZ=2  σ(QCD) ~ (1+ iαs/π), JZ=0 σ(QCD) ~ (1+jαs/π) i[O(1)] < j

    (for JZ=0 + QCD contribution O(α2) via γγ qqgg andγγ qq(g)qq ) (MadGraph)

  • Response of a detector simulated withSIMDET V4

  • Ws are reconstructed fromhadronic final states

  • Estimated errorsof measurement ofand parameters,obtained by fit (binned Likelihood )


Pileup rejection

track selection via impact parameterI (xy, z)

pileup

clean

Reconstructed PV of an event as the momentum weighted average impact parameter IZ of all tracks, using the information from VTX

Reconstructed IZ of each good/bad track normalized to its error

Separation efficiency

  • All neutral accepted

  • neutral + tracks with θ > 7º


After impact parameter IXY < 2σXYcondition

signal + pileup

tracks

pileup tracks

signal tracks

signal with pileup

  • All neutral accepted

  • neutral + tracks with θ > 7º

clean signal


γγ qq  4jetsBackground

- used luminosity spectra (with mixed JZ=0 and JZ=2 states  σmix)

Born Levelσ2 >> σ0

JZ=2:σ2

JZ=0:σ0 ~ σ2∙(m2/s)  suppression

J2 contribution for

dominating J0

NLO correctionsk2QCD < k0QCD

JZ=2:k2QCD ~ (1+iαs/π)

JZ=0:k0QCD ~ (1+jαs/π)i < j

J0+J2

J0 ↔J2

1-loop

non-Sudakov

form factor

Corrections to the Born Level σ

JZ=2:γγ qq (O’Mega)+ QCD (4-5%) parton shower well described

by Lund model (q  qg soft gluons);

J0 ( 0) and J2  dominates in σmix

JZ=0:γγ qq(O’Mega) σ0Born << σ2BornJ2 dominates in σmixbut…

O’Mega σ0Born 0 due to the (m2/s) suppression


Correction toσγγ qq in the JZ = 0 state

σ0QCD→ 0 (m2/s) suppression canceled by double-logarithms (two-loop)

QCD corrections to the Born Level σin JZ = 0 > σ2QCD

Pure JZ=0 (whole spectrum):

MadGraph  γγ qqgg + qq(g  qq)

(O’Mega does not calc. QCD)

MINV(3,5,6,9,10,12)> 30 GeV

MINV(3,5,6,9,10,12)> 30 GeV

… and added to γγqq (O’Mega) with JZ =0


Selection

εff ≈ 97%

εff ≈ 47%

Accepted events: NENFLO > 40, NCT > 20

40º < accepted events < 140º

εff ≈ 11%

εff ≈ 88%

WF cosθ > 0

WB cosθ < 0

J1,J2  WF

J3,J4  WB


εff ≈ 53%

εff ≈ 1.8%

(MW1+MW2) > 125 GeV

+ 60 GeV < MW1,MW2 < 100 GeV

εff ≈ 52%

εff ≈ 1.9%


Final angular distributions for JZ=0

WF

WB

similar distributions for JZ=2

Events made of

pileup

tracks only

pileup


Monte Carlo Fit

Each event described with 5 kinematical variables (sensitive to TGC) :

  • - W production angle,cosθof W boson

  • - W polar decay angles,cosθ1,2 (sensitive to the different W helicity states)

  • azimuthal decay angles,1,2(sensitive to the interference between different W helicity states)

Matrix element calculations (O’Mega)  weights to reweight SM events (Δκγ=0, Δλγ=0) as functions of anomalous TGC by

Weight/event:

R(,) = 1 + A· + B·()2 + C· + D·()2 + E · 

+ 6-th dimension  cme

ND=NSM-data sample (SM),NMC- Monte Carlo sample[NSM·R(,)],L– error on luminosity measurement


Error Estimations

Estimated errors for and - two-parameter + n6D fit


2-dimensional contour plots

JZ=0

JZ=0

JZ=2

ΔL = 0.1%

ΔL = 0.1%

95% CL

ΔL = 1%


400 GeV % 800 GeV

Estimated errors for and - two-parameter + n (5D fit)

(generator level, fixed beam energy)


γe: Real / Paras.

γγ :JZ=2/ JZ=0

¹ generator level

e- & e+ pol.

Scaled for bkg.,

spectrum, pileup


Systematic Errors

  • Polarization influence on  and 

  • Data sample- 1% changed polarization JZ=2/JZ=0 in the sample with P0,2= + 0.90 JZ=0/JZ=2

    (realized increasing Nev with JZ= 2,0 for 10%  increase of Nev corresponds to the P0,2 = + 0.89)

    fit (with MC):JZ=0 (L= 1%)  ,λγshifted <1

    JZ=2 (L= 0.1%)  shifted <3, shifted < 1

  • Effect of the background

    Data sample

    Estimated background per bin is changed for both modes, fit (with MC):

    (L= 0.1%)

    JZ=2→ for κγshifted by 1σ→ bck. at level of < 0.8%, for λγ< 4%

    JZ=0 → for κγ shifted by 1σ→ bck. at level of < 1.1%, for λγ< 0.6%

    (L= 1%) for κγ shifted by 1σ→bck. at level of ~ 15%,for λγ< 0.6%


Conclusions

  • Pileup rejection is difficult (still has a large contribution – decrease: to enlarge ‘b’)

  • Good signal / background separation

  • Information on Δκγ in the cross-section (via n)

  • Information on Δλγin the shape of the distributions

  • Statistical error estimations Δκγ, Δλγ ~ 10-4

  • Systematic errors  background


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