QCD with W/Z-events

1
QCD with W/Z-events

• Ursula Bassler, LPNHE-Paris
• in behalf of the CDF and DØ collaborations

• Basics on W/Z at the Tevatron
• W/Z-production
• Drell-Yan cross-section
• d?/dPT for W and Z
• W/Zjet production
• W-decay
• angular dependence of decay lepton
• lepton charge asymmetry

2
Basics of W and Z production

• W/Z production from qq annihilation
• ?, pT distribution depend on pdf
• large production
• selection based on leptonic decays
• W ? l? (BR 11 per mode)
• ET(l) gt 25 GeV, ET(?) gt 25 GeV
• Z ? ll (BR 3 per mode)
• 2 isolated leptons, ET(l) gt 25 GeV
• Run 1A 20 pb-1 Run 1B 80 pb-1
• (Run 0- CDF 4pb-1)
• ? 60k W-events, ? 5k Z-events /exp.

l
l
kinematic variables
3
Drell-Yan cross-section

• access region at x gt 0.02 and up to Q2?15000
  GeV2
• high mass Drell-Yan sensitivity to new physics
• good agreement with NLO-calculation

4
Drell-Yan cross-section low mass

• update of low mass Drell-Yan cross-section with
  reduced statistical errors
• ee and ?? channel in good agreement
• consistent with expected behavior

5
Drell-Yan at high rapidity

• special analysis with leptons in the forward
  region
• y1/2 ln x2/x1
• access high x region
• good agreement with gluon resummation calculation

6
pT dependence in W/Z-production
,W
q
q
q
,W
,W
q
q
q

• O(?) W/Z bosons produced with pT0
• pT attributed to gluon radiation, expected to
  broaden with Q2 M ? 10 GeV ??
  ltpTgt ? 1 GeV
• M ? 80 GeV ? ltpTgt ? 5 GeV
• M ? 91 GeV ?? ltpTgt ? 6 GeV
• measurements of d?/dpT
• W ? higher statistics, Z ? better resolution

7
Z-production at high pT

• d?/dpT(Z) measured at 1 lt pT lt 230 GeV
• cross-section falls over 5 orders of magnitude
• perturbative QCD at O(?2) describes data at high
  pT

8
Z-production at low pT

• at low pT soft gluon radiation dominates
• resummation of large ln(Q2/pT2) terms
• pT ?0 parameterize non-perturbative contribution

• 2 formalisms possible
• b-space resummation ? impact parameter space
• qT-space resummation ? transverse momentum space

9
fit of Sudakov Form Factor

• best description from
• Ladinsky-Yuan
• parameterization
• fit to low mass Drell-Yan
• and d?/dpT from CDF on
• Run 0 data

• non-perturbative Sudakov Form Factor
• SNPLYg1b2g2b2ln(Q2/Q02)g1g3b ln(100xixj)
• new fit of g20.590.06 GeV2 , reduced error
• g1 and g3 in agreement with LY-value, similar
  error

10
pT dependence in W-production

• d?/dpT(W) measured at 1 lt pT lt 180 GeV
• error dominated by
• low pT hadronic resolution
• high pt statistics and backgrounds
• good agreement with NNLO QCD low pt gluon
  resummation

• DØ preliminary
• MRSA - NNLOres.

11
W/Zjet production

• hard gluon radiation produces additional jets
• ?(W/Z ?1j)/?(W/Z)
• depends on ?S
• ?(W/Z ? Nj) in good agreement with
• LO-calculation
• soft scale ltpTgt2 favored

12
angular dependence in W-decay
?2
in W-rest frame
q
O(?)
sq
sq
sW
g
q
QCD
sq
sq
sW
13
charge asymmetry in W-decay
W
W-
u
d

• constraints d/u ratio
• measurement at Q2?M2W and 0.006 lt x lt 0.34
• CDF combined e?
• DØ ? only

14
Conclusions

• W and Z bosons allow QCD studies using leptonic
  signatures, both in production and decay
• Run II will start in march 2001
• increased statistics (2 fb-1 / 2 years)
• improved detectors
• new and interesting results!