Production of Gauge Bosons at the Tevatron

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Production of Gauge Bosons at the
Tevatron Recent Results Harry Melanson Fermilab
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A shopping list of W, Z Tevatron topics
Pick recent results with a QCD flavor
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Introduction to W, Z Production at the Tevatron
p
l
q
O(as0)
W(Z)
n (l )

• Production dominated by qq annihilation (60
  valence-sea, 20 sea-sea)
• Due to very large pp jj production, need to
  use leptonic decays
• W en, W mn, W tn (BR 11 per mode)
• Z ee, Z mm (BR 3 per mode)
• Leptonic decay features
• W High PT isolated lepton, Large missing
  transverse energy
• Z Two high PT isolated leptons

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Introduction to W, Z Production at the Tevatron
D0 W en
D0 Z ee
Benefits of studying QCD with Ws and Zs

• Distinctive event signatures
• Low backgrounds
• Large Q2 (Q2 Mass2 6500 GeV2)
• Well understood Electroweak Vertex

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QCD Corrections O(as )
O(as)
q
q
W
q
W
W
g
g
q
q
q
Modifications due to QCD corrections

• Inclusive cross sections larger (K factor 18)
• Boson produced with transverse momentum ( lt PT
  gt 10 GeV )
• Boson jet events possible ( W 1 jet 7,
  ETjet gt 25 GeV )
• Boson decay angular distribution modified

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Connections between W,Z Production, QCD and New
Physics
Inclusive Cross Sections
Measure
SM EW
Form ratio
W Width
Perturbative QCD
LEP measurement
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Indirect vs Direct W Width Measurements
Vertex Corrections same for quarks and leptons,
so cancel in BR(W ln)
Rosner, Worah, Takeuchi, hep-ph/9309307
W decays
Kalinowski and Zerwas hep-ph/9702386
Indirect has no sensitivity to corrections to the
coupling of the W to fermions, but is sensitive
to possible non-standard model decay modes of the
W.
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Inclusive Cross Sections
NEW
Updated

• Measurement errors Stat Å Sys 2,
  Luminosity error 4
• Theory error 3, NNLO, O(as2) (Hamberg, van
  Neerven, Matsuura)
• Dominated by PDFs at NLO(need NNLO)
• NB Luminosity determination L(D0) 1.062 x
  L(CDF)
• D0 uses world avg. s(pp)inel, CDF uses CDF
  measurement

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Inclusive Cross Sections
NNLO theory
NNLO theory
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New
D0 preliminary
R 10.43 0.15 (stat) 0.20 (sys) 0.10
(theory) B(W en) 0.1066 0.0015 0.0021
0.0016
2.6 total error
Luminosity error cancels in the ratio
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W Width
NEW
(Preliminary)
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Inclusive Cross Sections
D0 preliminary
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Inclusive Cross Sections
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Connections between W,Z Production, QCD and New
Physics
W boson mass top quark mass Constrain Higgs
mass
Need precise model of W production and decay for
Monte Carlos
W mass measurements require low PTW
Non-perturbative QCD
NLO QCD
Resummation techniques
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Introduction to W, Z PT Theory

• Large PT region (PT ³ 30 GeV) Use pQCD, O(as2)
  calculations exist

Ellis, Martinelli, Petronzio (83) Arnold Reno
(89) Arnold, Ellis, Reno (89) Gonsalves,
Pawlowski, Wai (89)

• Small PT region (LQCD lt PT lt 10 GeV) Resum
  large logs ln(Q2/PT2)

Altarelli, Ellis, Greco, Martinelli (84)
Collins, Soper, Sterman (85)

• Very low PT region (PT LQCD) Non-perturbative
  parameters extracted from data

b-space Parisi-Petronzio (79) Davies-Stirling
(84) Collins-Soper-Sterman (85) Davies, Webber,
Stirling (85) Arnold- Reno-Ellis (89) AK
Arnold-Kaufann (91) LY Ladinsky-Yuan
(94) qt-space Dokshitser-Diaknov-Troian (80)
Ellis-Stirling (81) Altarelli-Ellis-Greco-Martine
lli (84) Gonsalves-Pawlowksl-Wai (89) ERV
Ellis-Ross-Veseli (97) Ellis-Veseli (98)
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Recent W,Z PT measurements

• W PT
• D0 Run 1b electrons (82 pb-1)
• (Compared to AK O(as2) b-space)
• CDF Run 1a1b electrons (110 pb-1)
• (Compared to ERV O(as) bqt space)

NEW

Recent

• Z PT
• D0 Run 1b electrons (82 pb-1)
• (Compared to AK O(as2) LY O(as) b-space)
• CDF Run 1a1b electrons (110 pb-1)
• (Compared to O(as) LY b-space ERV O(as)
  qt-space)

• Ws vs Zs
• W x10 more statistics
• Z Better PT resolution, lower backgrounds

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D0 W PT measurements
New
Arnold-Kauffman Nucl. Phys. B349, 381 (91).
O(as2), b-space, MRSA (after detector simulation)
Preliminary
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D0 W PT measurements
Preliminary
Arnold, Kauffman, Nucl. Phys. B349, 381. O(as2),
b-space, MRSA (after detector simulation).
c2/dof7/19 (pT(W)lt120 GeV/c) c2 /dof10/21
(pT(W)lt200GeV/c)
Resolution effects dominate at low PT High PT
dominated by statistics backgrounds
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CDF W PT measurements
Ellis, Ross, Veseli, NP B503, 309 (97). O(as), qt
space, after detector simulation.
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CDF Z PT measurements
ResBos Balasz, Yuan, PRD 56, 5558 (1997),
O(as2), b-space.
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CDF Z PT measurements
ResBos Balas, Yuan, PRD 56, 5558 (1997), O(as2),
b-space VBP Ellis, Veseli, NP B511,649 (1998),
O(as), qt-space
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D0 Z PT measurements
Preliminary
c2/dof 17/16
Ladinsky, Yuan, PRD 50, 4239 (94), O(as2),
b-space.
c2/dof 83/16
Arnold, Kauffman, NP B349, 381 (91), O(as2),
b-space.
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D0 Z PT measurements
Arnold, Reno, Nucl. Phys. B319, 37. O(as2),
MRSA, after detector simulation.
Preliminary
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Connections between W,Z Production, QCD and New
Physics
W boson mass top quark mass Constrain Higgs
mass
Current CDF/DØ dMW 5-9 MeV from PTW model dMW
10 MeV Þ dMH/MH 14
W production Monte Carlos tuned to Z data
NLO QCD
Non-perturbative QCD
Resummation techniques
W, Z PT distributions confirm formalism(s)
Z PT distributions constrain non-pert. parameters
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W Decay Distribution
Angular distribution of electron in W rest frame
Pure V-A
Collins-Soper frame
NLO QCD corrections to production modify this
distribution
g
V-A
QCD
q
q
sq
sq
sW
sW
Mirkes, NP B387, 3 (1992) - O(as2).
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W Decay Distribution - a2
a2 vs PTW
V-A a2 1
V-A a1 1 D0 only sensitive to a2
Connections between W,Z Production, QCD and New
Physics
Including this effect in W mass Monte Carlo DMW
40 MeV (D0)
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D0 method to measure a2

• Use correlation between cosq and MTW to infer
  cosq on a statistical basis

• Define probability function

• For each PT (W) bin, plot background subtracted
  mT (W) and get

Bayesian

• Compare to ni templates from MC

• Use log-likelihood to determine best value of
  a2(PT (W))

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D0 method to measure a2
Extracted cosq distributions
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D0 method to measure a2
Log-likelihoods vs a2
PT lt 10 GeV
10 GeV lt PT lt 20 GeV
20 GeV lt PT lt 35 GeV
35 GeV lt PT lt 200 GeV
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W Decay Distribution - a2
V-A a2 1
Prob(V-A NLO QCD) 87 Prob(V-A only) 7
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Conclusions

• W, Z inclusive cross sections in good agreement
  with SM.
• Stat Å Sys 2, Luminosity error 4, Theory
  error 3
• Maybe use to determine luminosity in Run II.

• W width measurement (direct and indirect) in
  good agreement with SM.
• Indirect measurement error 3

• W, Z PT distributions measured.
• CDF D0 measurements over wide range of PT with
  errors 10 - 20
• Testing NLO QCD resummation non-perturbative
  models

• QCD correction to W decay distribution
  confirmed.
• D0 preliminary measurement of a2 vs PTW