Victoria Martin

1
W and Z Physics at CDF

• Victoria Martin
• Northwestern University
• La Thuile 2004

Contents Electroweak Physics at Run II CDF
Detector and Reconstruction Cross Section
Measurements Precision Measurements Conclusions
and Outlook
2
Why Electroweak Physics at Run II?

• Large numbers of W bosons
• High mass Z/? events
• Sensitive to u d quarks

Di-boson cross sections
Beyond SM Di-bosons couplings Zresonance anomal
ous q couplings
Tri-boson couplings
New Forward Detectors
W, Z cross sections
Z Forward-Backward Asymmetry
W asymmetry
sin2(?W), quark couplings
Indirect G(W)
Higgs Mass Constraint
W mass
Lepton Universality
Direct G(W)
3
Run II Luminosity

• Tevatron has delivered 430 pb-¹
• We have 350pb-¹ on tape.
• Analyses presented here are using either 72
  pb-¹, 120 pb-¹ or 200 pb-¹ of data
• Error on luminosity is 6. Limited by knowledge
  of pp inelastic cross section.

4
CDF Run II Detector

• From Run I
• Solenoid
• Central muon system
• Central calorimeter

Polar angle ?

• New For Run II
• Front-end DAQ
• Trigger
• Track (L1) and Displaced Track (L2)
• Silicon Tracker (8 Layers) (??? ? 2.0)
• Central Outer Tracker (??? ? 1.0)
• Plug Calorimeters (1.0 ? ??? ? 3.6)
• Extended Muon Coverage (??? ? 1.5, gaps filled in)

5
CDF Run II Detector
CentralPlug Calorimetery ??? ? 3.6
Muon Chambers ??? ? 1.5
Central tracking ??? ? 1.0
Silicon tracking ??? ? 2.0
6
Electron, Muon, Photon Neutrino Reconstruction
Plug electron EM calorimeter cluster (silicon,
COT hits may be attached)
Electrons
Neutrinos Large Missing Energy (Only Transverse
ET)
Central electron A track pointing to an EM
calorimeter cluster
1.0 ? ??? ? 2.8
??? ? 1.0
??? ? 1.0
Tight Muon An isolated track pointing to a
muon stub
??? ? 1.0
??? ? 1.1
Loose muon An isolated track pointing to a
gap in the muon coverage
Photons EM Calorimeter cluster with no
associated track
Muons
7
Inclusive W and Z Signals
8
Inclusive W cross section

• W?µ? signal
• tight muon plus large ET
• W?e? signal
• central electron plus large ET
• Backgrounds from QCD, Z?ll-, W?t? and cosmic (µ
  channel)

Candidate events in 72pb-1 Candidate events in 72pb-1 Estimated background Acceptance x efficiency
W ? µ? 31,722 (10.6 0.4) (17.940.36-0.33)
W ? e? 37,574 ( 4.4 0.8) (14.390.32-0.31)
9
Inclusive Z cross section

• Z ? e e- signal
• 2 central electrons (CC)
• 1 central plus 1 plug electron (CP)
• Z ?µ µ- signal
• one tight muon plus one track
• 66 lt m(ll)/GeVc-2 lt 116
• Small backgrounds from QCD, Z/W?t, cosmics (µ)
  less than 1.5

Number of candidates in 72pb-1 Number of candidates in 72pb-1 acceptance x efficiency
Z ? e e- (CC) 1730 (22.74 0.47-0.48)
Z ? e e- (CP) 2512 (22.74 0.47-0.48)
Z ? µ µ- 1785 (10.18 0.24-0.28)
For 66 lt m(ll)/GeVc-2 lt 116
10
W?t? and Z?tt- Signals

• Look for hadronic tau decays
• Narrow isolated jet
• Low track multiplicity
• invariant mass of tracks and p0 lt m(t)
• 2345 candidate events in 72pb-1

• Z?tt- signal
• 1 hadronic tau decay (jet)
• 1 t?e? or t?µ? decay
• Backgrounds from Z?ll-, QCD

11
Combining e and µ channels

• Assuming lepton universality, combine W and Z
  results
• correlated systematics effects accounted for

12
BR(W?l?) and G(W)
3.36770.024 NNLO (PDG)
From LEP (3.366 0.0002)
Using NNLO calculation G(W?l?)226.4 0.4 MeV
(PDG)
Current World Average 209242 MeV
13
Lepton Universality

• Calculate R separately for e and µ channels

• From a measurement of yields from a t trigger,
  we extract an value for the ration of t and e
  couplings

14
Z?ee- Forward-Backward Asymmetry
P
angle between p and e-

• Tevatron is uniquely sensitive to Z-?
  interference at high invariant masses.
• Shape of the Afb spectrum can be used to extract
  values for sin2(?W) and u, d couplings to Z
• Agreement with SM prediction.

15
Di-boson Signals
W ?
Z ?
Triple Boson Coupling
Non SM!
16
Di-boson production W?

• pp ? W? ? l??
• One tight high-PT lepton (e,µ)
• One Photon with
• ETgt7GeV
• ?R(?,l)gt0.7
• Large missing-ET
• Backgrounds from QCD, Z?
• Probes electroweak boson self-coupling, new
  physics

ET(?)
?R(?,l)
Candidate Events in 202 pb-1 Candidate Events in 202 pb-1 estimated background
W?? e?? 131 (25 6)
W?? µ?? 128 (32 5)
NLO prediction (U. Baur)
(LO ET(?) dependent k factors)
17
Di-boson production Z?

• pp ? Z? ? ll?
• Two oppositely-charged high-pT leptons
• One photon with ETgt7GeV, ?R(?,l) gt 0.7
• Small backgrounds (10)

Candidate events in 200 pb-1 Candidate events in 200 pb-1
Z?? ee? 34
Z?? µµ? 35
NLO prediction (U. Bahr)
(LO ET(?) dependent k factors)
18
Di-boson production WW-

• pp ? WW ? l?l l?l
• Two oppositely-charged high-pT leptons
• Large missing-ET
• Veto events with jets
• Veto Z background
• 76ltmee, mµµlt106 GeV/c2
• 5 candidate events in 126pb-1
• (2.30.4) background expected from Drell-Yan,
  QCD, WZ and tt.

NLO calculation Campbell Ellis
hep-ph/9905386
19
Towards W Mass and Asymmetry
Work in progress no results yet

• Use MC templates to fit to signal background
• CDF Run I mW 80,465 100(stat) 104(sys) MeV
• CDF Run II for 500/pb (estimated)
• X 40(stat)
  55(sys) MeV

Sensitivity to u/d fraction PDFs
High mT tail is sensitive to G(W)
20
Conclusions

• We have measured the cross section for pp
  collisions at vs1.96 TeV
• W?l? for electron, muon, tau channels
• Z?ll for electron and muon channel
• Di-bosons W?, Z?, WW
• Extracted first results on electroweak
  parameters
• Indirect measurement of G(W)
• Lepton universality
• All results consistent with Standard Model no
  sign of New Physics (yet!)
• Look for CDFII first results on W-mass, W
  asymmetry, direct G(W), sin2(?W) and boson-quark
  couplings, all coming soon!