# Presentation: 446278

## Recent results from EW and Top Quark Physics at DØ

- Leonard Christofek
- University of Kansas
- On behalf of the DØ Collaboration

- Tevatron Connection

## Gauge Boson Couplings

- The standard model makes very stringent predictions for (i.e. uniquely determines) the trilinear couplings of the gauge bosons: W, Z,   and .
- These couplings can be investigated by measuring W and Z production, as well as WW, WZ, and ZZ pair production.
- The presence of anomalous couplings would indicate physics beyond the standard model.
- Parameterized by an effective Lagrangian.  Spin 1 boson will have four parameters.

## W Production

- Requires efficient photon identification.
- Event selection:
- High PT isolated electron or muon,
- Missing transverse energy,
- Isolated photon with ET > 8 GeV || < 1.1 and R(l,) > 0.7.
- Photon ID efficiency                 = 81 ± 1 %.
- Main background is W+jets production where the jet mimics a photon.  Estimated from data.
- Background for important high PT analyses: HWW, top, trileptons.

## W Production Cross Section 

-  Theory cross section: (ppWl) = 16.0 ± 0.4 pb.
-  Combined electron and muon cross section:    L = 162 (134) pb-1   (ppWl) = 14.8 ± 1.6(stat) ± 1.0(syst) ± 1.0(lumi) pb.
-  In the absence of an excess of large ET photons, extract limits on the anomalous couplings.

- Fermilab-Pub-05-046-E

## W Anomalous Couplings 

-  Binned maximum likelihood fit to the photon ET spectrum.
-  Limits on CP conserving couplings ( = 2 TeV):
-                   -0.88 <  < 0.96       -0.20 <  < 0.20
-  Limits on non-CP conserving couplings in progress.

- 95% C.L.
- contour

- Fermilab-Pub-05-046-E

- 1-d

- 2-d

## Radiation Amplitude Zero

- For cos , the angle between incoming quark and photon in the W rest frame, equal to 1/3, the differential cross section goes to zero.  This is a radiation amplitude zero.
- Endcap photon identification necessary to get a statistically significant signal.  In progress...
- Background subtraction important (M(W,) > 90 GeV/c2).

- DØ Preliminary Muon Channel

- MC

- () - (*l*)  -0.4

## Z Production

- Requires efficient photon identification.
- Event selection:
- Two high PT isolated electrons or muons (oppositely charged),
- Isolated photon with PT > 8 GeV, || < 1.1 and R(l,) > 0.7.
- Photon ID efficiency                 = 81 ± 1 %.
- Main background is Z+jets production where the jet mimics a photon.  Estimated from data.

## Z Production Cross Section

-  Theory cross section: (ppZll) = 3.9 + 0.1 - 0.2 pb.
-  Combined electron and muon cross section:   L = 320(290) pb-1   (ppZll) = 4.2 ± 0.4 (stat+sys) ± 0.3 (lumi) pb.

|  | Electron | Muon |
| --- | --- | --- |
| SM | 95.3 ± 4.9 | 126.0 ± 7.8 |
| Bkgd | 23.6 ± 2.3 | 22.4 ± 3.0 |
| Data | 138 | 152 |

- Z Event Yields

- Fermilab-Pub-05/023-E

## Z Anomalous Couplings

- Fermilab-Pub-05/023-E

-  Limits on CP even and CP odd couplings for ZZ ( = 1000 GeV):
-                   | hZ10,30 | < 0.23,        | hZ20,40 | < 0.020
-  Limits on CP even and CP odd couplings for Z ( = 1000 GeV):
-                   | h10,30 | < 0.23,        | h20,40 | < 0.019

- 95% C.L.
- contour

- Unitarity constraints

- Z0 ISR

- Z0 FSR

- DY ISR

## WW Production

- WW production is major background for searches (Higgs, SUSY).
- Provides another channel to search for anomalous couplings (WW and WWZ).
- Theoretical prediction:
- (WW) = 13.5 pb @ 1.96 TeV
- Main backgrounds:
- Z/, top pair production, WZ, ZZ, W+jet/, multijets.

- Campbell & Ellis

## WW Production

- Event selection:
- Two high PT isolated oppositely charged electrons or muons,
- With PT > 20 GeV and PT > 15 GeV,
- MET > 30, 40, 20 GeV  in ee, , e to remove Z/*.

- Missing transverse energy after event selection.

## WW Production Cross Section

-  **hep-ex/0410066**

-   e channel:
-  no third lepton such that 61 < M(l+l-) < 121 GeV/c2.
-  minimal transverse mass > 20 GeV/c2.
-  HT (jets w/ET > 20 and || < 2.5) < 50 GeV.
-  Summary:
-  6 ee candidates, exp. signal/background: 3.4 and 2.3.
-  4  candidates, exp. signal/background: 2.1 and 1.9.
-  15 e candidates, exp. signal/background: 11.1 and 3.8.
-  Anomalous coupling extraction in progress:
-  || < 1.2   || < 1.0  95% C.L.  = 1000 GeV (Run I).

- P(background fluctuation) = 2.3  10 –7
- Corresponds to 5.2  significance.

## WZ Production

- Trilepton events:
-  At least two high PT >15 GeV/c isolated electrons or muons that make a Z boson,
- A third isolated *e* or  with high PT,
- Missing transverse energy > 20 GeV.
-  (WZ) ~ 4.0 pb @ 1.96 GeV.
- Only sensitive to WWZ coupling.

- Campbell & Ellis

## WZ Production Cross Section

-  Main background is Z+X (X = j, , or Z).
-  2  and 1 *eee* candidates.
-  P(0.71 bkgd)  3 signal events is 3.5%.
-  Cross section (WZ) = 4.5+3.5-2.6 pb
-  standard model cross section:
-  (WZ) = 3.7 ± 0.1 pb

- Dielectron Channel

- Dimuon Channel

- D0 Preliminary

## WWZ Anomalous Couplings

- Best limits in WZ final states.
- First 2-d limits in Z vs Z  using WZ.
- Best limits available on g1Z, Z, and Z from direct, model independent measurements.
- Factor of 2-3 improvement of Run I.

- DØ Preliminary

- 95% C.L.

- Unitary boundary

## Z Boson Rapidity Distribution

- Complimentary measurement to high-momentum jet spectrum PDF’s.
- Advantage: Z/DY process rapidity distributions calculated at NNLO.
- Measure at high Q2 , large and small Bjorken x in the initiating quark and antiquark.
- Can be used to constrain the parton distribution functions.
- Two high PT isolated electrons that make a Z boson:
- 71 GeV/c2 < M(ee) < 111 GeV/c2
- Integrated luminosity = 337 pb-1
- Good agreement with prediction.

## W Boson Width

- W boson width is predicted precisely to be W = 2.090 ± 0.008 GeV (Hagiwara et al. D66 (2002)).
- High values of MT are sensitive to the width of the W boson (Breit-Wigner lineshape).
- Integrated luminosity = 177 pb-1
- Event selection:
- High PT electron
- Missing transverse energy
- Backgrounds:
- Multijets
- Z *ee*, one electron undetected
- W   * e*
- Binned maximum likelihood fit:
- 100 GeV < MT < 200 GeV

- W = 2.011 ± 0.093 (stat) ± 0.107 (syst)
- Calorimeter calibration in progress. One inverse femtobarn can give ~25 GeV (stat.) and ~45 MeV (syst.) totaling ~50 MeV.

## The Top Quark Event Signatures

-  At Tevatron, top pair production mainly from qq (85%) and gg (15%).
-  In standard model, top decays 99.9% of the time to Wb.  It decays before it hadronizes.
-  Event classification:
- all hadronic (all jets), lepton plus jets, dileptons.
-  Need to identify and reconstruct:
- electrons, muons, jets from b-quarks, jets from light quarks, missing transverse energy.

- Top pair decay modes

## Top Quark Event Signatures

- Dilepton:
- Signal selection:
- Two high PT leptons
- Missing transverse energy
- Two or more high PT jets
- Backgrounds:
- Diboson (WW, WZ, ZZ)
- Drell-Yan
- Z  
- W + jets with fake lepton

- Lepton plus jets:
- Signal selection:
- One high PT leptons
- Missing transverse energy
- Four or more high PT jets
- Backgrounds:
- W + jets
- Multijet with fake lepton

- Use b tagging to
- increase S/B.

## Top Pair Production Cross Section

## Top Quark Mass

- Top mass measured in two channels with 0.25 fb –1.
- Currently improving measurement of jet energy calibration.
- Expect improved results soon.

## W Helicity Top Quark Decays

- In standard model, W helicity depends on the top quark and W boson masses:
- Predicted 70% longitudinal, 30% left-handed, and 0% right-handed.
- We measure right-handed fraction f+ or V+A component.
- Any deviation is a signal for new physics:
- SU(2)L SU(2)RU(1)Y models [PRL **38**, 1252 (1977)].

-  Use the angular distribution cos *:
- Angle between the charge lepton and top quark direction in the W boson rest frame.
-  Event selection:
- High PT isolated electron or muon,  four jets, missing ET.
- Two parallel analyses: topological, which uses only topological information, and b-tag, which requires at least one jet tagged by the SVT.

## W Helicity in Top Quark Decays

-  Analyses use binned maximum likelihood fit to extract f+ : cos * from data, cos * from signal and background contributions.
- Topological analysis (230 pb-1):
-  35 events observed in data
-  Expected yield for signal and background: 17 and 19, respectively.
-  b-tag analysis (230 pb-1):
-  52 events observed in data
-  Expected yield for signal and background: 41 and 13, respectively.

- Topological

- b-tag

## W Helicity in Top Quark Decays

-  Systematics include:
-  jet energy calibration,
-  top quark mass,
-  signal and background MC.
-  Topological analysis:
-  f+ < 0.25 @ 95% Bayesian C.L.
-  b-tag analysis:
-  f+ < 0.25 @ 95% Bayesian C.L.
-  Dilepton analysis now under collaboration review.

- Combined result:
- f+ = 0.00 ± 0.13 (stat) ± 0.07 (syst)
- f+ < 0.25 @ 95% Bayesian C.L.

## Single Top Quark Production

-  Event Selection:
-  One high PT isolated lepton,
-  From 2 to 4 jets:
- Leading jet > 25 GeV,
- PT > 15 GeV   || > 25 GeV.
-  s-channel 1 or more b-tagged jets,
-  t-channel 1 or more b-tagged jets
-  and 1 or more untagged jets.

- s-channel  NLO ~ 0.88 pb

- t-channel  NLO ~ 1.98 pb

## Single Top Quark Production

-  Backgrounds:
-  W/Z + jets production,
-  Multijet production
-  Top pair production,
-  Diboson (WZ, WW).
-  Use neural networks to improve sensitivity.

## Single Top Quark Production

-  No evidence for single top quark production.
-  Set Bayesian 95% C.L. upper cross section limits:
-  	s < 6.4 pb      t < 5.0 pb
-  Presently, most sensitive limit in the world.

## Summary

- This is just the beginning:
- Electroweak analyses in progress:
- W charge asymmetry in e + , Z PT distribution, W cross section, etc...(Z cross section, W and W*e* cross sections)
- Top quark analyses in progress:
- Top charge, top pair resonances, top decay to charged Higgs,  anomalous kinematics (PT of top quark), top mass in all jets channel, etc...
- Reached one inverse femtobarn: 1fb-1.
- For more details on results available:
- http://www-d0.fnal.gov/Run2Physics/WWW/results.htm