Klaus M

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Klaus Mönig and Jadranka Sekaric
DESY - Zeuthen
MEASUREMENT OF TGC IN e? COLLISIONS AT TESLA
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T E S L A
INTRODUCTION

• In order to predict the precision of measurement
  of trilinear gauge couplings (TGC) at a photon
  collider
• signal to background separation study (e? ?W? )
• for real and parasitic e? -mode
• observables sensitive to TGC
• (angular distributions, cross-sections )
• estimated errors, ??? and ??? of measurement of
  ?? and ?? parameters, obtained by
  fit-minimizing the ?2 value
• - effect of photon beam polarization on ??? and
  ??? measurement

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T E S L A
EVENT SELECTION

• TOOLS
• PYTHIA event generator
• SIMDET V3 detector simulation
• sample of 105 mixed signal and background events,
  generated with PYTHIA at ECM (e?) 450 GeV
• background for real and parasitic e?-mode
• e? ? ?W ? ?qq ?T ? 37 pb
• e? ? eZ0 ? eqq ?T ? 3.5 pb
• ?? ? qq ?T ? 137 pb
• ?? ? WW ? l?qq ?T ? 82 pb
• ?? ? qq ?T ? 128 pb
• response of a detector simulated with SIMDET V3
• Ws are reconstructed from hadronic final states

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sufficiently high W production cross-section
allows us to efficiently separate signal from
background
T E S L A

• Applied cuts
• acceptance of detector - 7

?? ? qq
e? ? ?W
e? ? eZ0

• angular distributions for signal and bck.
  hadronic final states

• W energy
• (100-250) Gev

• hadronic final states energy spectrum

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T E S L A
?? ? qq
e? ? ?W
e? ? eZ0

• W mass
• (60-100) Gev

High efficiency for hadronic channel, 84 with
low background

• hadronic final states mass spectrum

• final angular distributions after selection

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T E S L A
Background for parasitic e? mode ?? ? WW ?
l?qq same cuts as previous ?? ? qq

• Applied cuts
• acceptance of detector - 7

e? ? ?W
?? ? qq
?? ? WW
angular distribution

• W energy
• (100-250) Gev

energy distribution
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T E S L A

• W mass
• (60-100) Gev

qq
?W
WW
mass distribution
S/BWW 91, purity 90
angular distribution after selection
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T E S L A
OBSERVABLES SENSITIVE TO TGC
total and differential cross-section

• analytic formula for total (differential)
  cross-section (A. Denner, A.Dittmaier,
  Nucl.Phys. B398 (1993)239
• helicity amplitudes for different initial photon
  and final W states (E.Yehudai, Phys.Rev.
  D11(44)1991))
• differential cross-section distribution over the
  decay angle (Bilenky at al.,Nuc.Phys. B(409)
  (1993)22
• WHIZARD Monte Carlo treelevel generator
  (W.Kilian,University of Karlsruhe)

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T E S L A
ANOMALOUS TGC can affect the total production
cross-section and the shape of the differential
cross-section
DCS in presence of anomalous coupling for J?
1 state normalized to its SM value
DCS for J? 1 state in SM
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T E S L A
Contribution of each helicity state of the W
boson ? affects the distribution of their decay
products
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T E S L A
MONTE CARLO FIT

• WHIZARD Monte Carlo generator, 106 mixed pairs
  (du-bar and sc-bar) at ECM 450 GeV, fixed
  photon-beam energy, polarized beams (P100),
  anomalous couplings
• for each event we observe 3 kinematic variables
• -W production angle with respect to the e- beam
  direction - cos?
• -W polar decay angle - angle of the fermion with
  respect to the W flight direction measured in the
  W rest frame cos?1
• -azimuthal decay angle ? of the fermion with
  respect to a plane defined by W and the beam axis
• Monte Carlo SM events are reweighted with
  function R(??????) (??? and ??? are free
  parameters)

R(??????) 1 A??? B??? C(???)2
D(???)2 E ??? ???
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T E S L A

• 2D (over cos?, cos?1 ) and 3D (over cos?,
  cos?1,? ) cross-section distributions are fitted

?L-error on the luminosity measurement norm-normal
ization constant
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T E S L A

• Estimated errors of ?? and ?? for 1 photon
  polarization state (P100) single parameter 2D
  and 3D fit

real mode/ parasitic mode ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 2D ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 2D ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 2D
real mode/ parasitic mode J? 1 J? 1 J? 1
?L 1 0.1 accurate
??? 10-3 3.6/3.7 1.0/1.0 0.4/0.4
??? 10-3 1.5/2.2 1.5/2.2 1.4/2.1
real mode/ parasitic mode ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 3D ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 3D ECM 450 GeV, ?L?t 110 fb-1 Monte Carlo 3D
real mode/ parasitic mode J? 1 J? 1 J? 1
?L 1 0.1 accurate
??? 10-3 3.0/3.1 1.0/1.0 0.4/0.4
??? 10-4 2.6/2.9 2.6/2.9 2.6/2.9
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T E S L A
??1.01
- ? distribution slightly decreases error of ??
(?L 1) and of ?? for a factor 7 ! ? shape
sensitivity in phi distribution ? phi
distribution influences much more on
??? 3D - Mean error on ?? comes from ?L, not
case for ?? - Good agreement between 2
modes for ??? and ???
??0.01
??-0.01
??0.99
?2
2D
3D
??
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T E S L A

• Polarization influence on ?? and ??
• ? variation of laser polarization in the laser
  wave
• ? beam field influences the photon polarization
• sample with P?0.9 polarized photons
• ? mixing the events with P?1 and P?-1 in
  order to get preferred polarization (955)
• ? errors obtained from the fit are in a good
  agreement with previous ones
• sample with 1 different polarization
• ? increased the Nev with P?-1 for 10 ?
  increase of Nev correspond to the P?0.89 ?
  test-fit and
• we found 1 changes in polarization (accurate
  fit)
• ? ?? within 12?
• ? ?? within 1?
• Contribution from normalization and from
  polarization

J
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T E S L A
SUMMARY

• -Efficient signal to background separation for
  both e? modes
• - ??? ,??? 10-3 (error on luminosity
  measurement, ?L,
• is included)
• - Main contribution to the error of ?? comes from
  ?L
• Shape sensitivity for anomalous ?? in phi
  distribution decreases error of ??
• Variable polarization (1) affects the ??
  measurement
• Future plans
• Variable photon-beam energy in WHIZARD
• Resolution on reconstructed variables
• Background influences on error predictions

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