1 EPS2003, Aachen Nikos Varelas ELECTROWEAK & HIGGS PHYSICS AT DØ Nikos Varelas University of Illinois at Chicago for the DØ Collaboration International Europhysics Conference on High Energy Physics Aachen, July 17 – 23, 2003

2 EPS2003, Aachen Nikos Varelas Outline Status of Run II EW Results:   B for W & Z e/  channels Ratio of W/Z Production Cross Sections Combined Tevatron Results Run II W width Run I W mass & width Higgs Studies: WH and ZH Associated Production H  WW * Search Summary Also: Search on fermiophobic Higgs Searches – Drew Baden Top Quark Production at the Tevatron – Elizaveta Shabalina Performance of the DØ experiment in Run II – David Buchhloz

3 EPS2003, Aachen Nikos Varelas DØ at Fermilab TeVatron-RunII DØ Upgrade: Silicon, fiber tracker, solenoid, muon, daq, trigger, electronics Main Injector & Recycler Tevatron Chicago   p source Booster pp p p pp 1.96 TeV CDF DØ

4 EPS2003, Aachen Nikos Varelas Data Sample Tevatron performance improving Peak luminosity ~ 4 x Data samples presented here: 9/02-1/03 (~50 pb -1 ) Detector data collection efficiency 85-90%

5 EPS2003, Aachen Nikos Varelas W’s and Z’s at the Tevatron Production dominated by “annihilation” Run II will have >10 6 W’s & >10 5 Z’s Use leptonic decays of W and Z Avoids large contribution BR ~11% per mode for BR ~3% per mode for Clean, low background, event signatures High p T isolated leptons W: 1 high p T lepton + missing E T (from ) Z: 2 high p T leptons Cross Sections increase by ~10% from 1.8 to 1.96 TeV W  l  ~1 L = 2  10 32

6 EPS2003, Aachen Nikos Varelas L  42pb -1 Inclusive single electron trigger |  e | 25 GeV No track match required Acceptance*Efficiency = 10% Drell Yan + interference = 1.7% background removed by fitting a scaled shape 1139 Z  ee final candidates Z Production - Electron Channel

7 EPS2003, Aachen Nikos Varelas Z Production - Muon Channel L  32pb -1 Di-muon trigger 2 opposite charged muons, |   | 15 GeV At least one muon is isolated Acceptance*Efficiency = 16% Drell Yan + interference = 12% Background removed by fitting a scaled shape 1585 Z  final candidates

8 EPS2003, Aachen Nikos Varelas W Production – Electron Channel L  42pb -1 Inclusive high-p T single electron trigger |  e | 25 GeV E ̸ T >25 GeV Acceptance*Efficiency = 23% W  (MC, 1.7%)  Z  ee (negligible) contributions removed QCD background evaluated from data (3%) removed using the “matrix method” with track-match cut W  e final candidates

9 EPS2003, Aachen Nikos Varelas W Production - Muon Channel L  17pb -1 Inclusive high-p T single muon trigger |   | 20 GeV E ̸ T >20 GeV (corrected for the muon P T ) Acceptance*Efficiency = 13% W  Z  (9%) contributions removed background evaluated from data (6%) removed using the “matrix method” with isolation cut 7352 W  final candidates

10 EPS2003, Aachen Nikos Varelas W and Z Cross Section Summary Scaling with cm energy consistent CR Hamberg, WL van Neerven and T Matsuura, Nucl. Phys. B359 (1991) 343 [CTEQ4M pdf] Measurements consistent with SM predictions CDF and DØ Run II Preliminary

11 EPS2003, Aachen Nikos Varelas Ratio of W/Z Production Cross Sections Use previous  B measurements in ratio to extract  (W) – Indirect Method Many uncertainties cancel in ratio Run II Preliminary: Run I DØ Result: LEP Theory Use CTEQ6 pdf + errors Phys. Rev. D 61, (2000)

12 EPS2003, Aachen Nikos Varelas CDF- DØ Combined Results Extract W width  (W) from the ratio of W/Z production cross sections: CDF Run II Preliminary: DØ Run II Preliminary: Tevatron Run II Preliminary: Tevatron Run I Result: Tevatron Run I + II Preliminary:  Part I

13 EPS2003, Aachen Nikos Varelas CDF- DØ Combined Results Part I’ CDF and DØ Run II Preliminary

14 EPS2003, Aachen Nikos Varelas W-Mass Tevatron Run I Result W Mass Tevatron Run I result (July 2002) DØ: CDF: Tevatron: World: Part II Run I

15 EPS2003, Aachen Nikos Varelas W-Width Tevatron Run I Result Shape of transverse mass distribution for M T >90 GeV is affected by the W width – Direct Method Electron channel Part III Run I

16 EPS2003, Aachen Nikos Varelas Search for non-SM heavy particles that decay to lepton pairs Assume same quark/lepton couplings as SM Z DØ Run I limit: M Z’ > 670 GeV With 2 fb  sensitivity up to 1 TeV Z’  ee Search DØ Run II Preliminary M(ee) around the Z Data Bkg (QCD+DY/Z) Bkg (QCD only) 10x Z'(600GeV) DØ Run II Preliminary M e+e- (GeV)

17 EPS2003, Aachen Nikos Varelas Higgs Searches SM Higgs Boson: m H > GeV (95% CL) Direct searches by LEP m H < ~200 GeV Indirect result from fit to data Many additional Higgs bosons in other models Searches are underway at DØ Several fb -1 of data needed for observation Non SM processes enhance cross section Run II will provide stringent constraints to SM Higgs  M t < 2.5 GeV per exp (currently 5.1 GeV - combined)  M W < 40 MeV per exp (currently 59 MeV - combined) See talk by Drew Baden on fermiophobic Higgs H  WW*, H  

18 EPS2003, Aachen Nikos Varelas Higgs Decays M H [GeV] Excluded Search strategies are a function of Decay Channel and Production Channel High Mass Higgs Searches Low Mass Higgs Searches ZH, WH

19 EPS2003, Aachen Nikos Varelas W(e  or  )+Jets Electron selection |  e | 20 GeV E ̸ T >25 GeV Muon selection |   | 25 GeV E ̸ T >20 GeV Jet selection |  jet | 20 GeV 1 st leading jet 2 nd leading jet JES uncertainty shown Combined MC=PYTHIA + Detector Simulation W(e  or  )+Jets

20 EPS2003, Aachen Nikos Varelas W(e  or  )+Jets – Dijet Mass

21 EPS2003, Aachen Nikos Varelas Z(ee  or  )+Jets Electron selection |  e | 20 GeV Muon selection |   | 15 GeV Jet selection |  jet | 20 GeV MC=PYTHIA + Detector Simulation

22 EPS2003, Aachen Nikos Varelas H  WW*  ℓ + ℓ - Search for high mass Higgs SM extensions enhance the production cross section Signal: dileptons + E ̸ T Bkgd: Z/  *, WW, t t, W/Z + j, QCD Opening angle between leptons is useful discriminating variable Two leptons tend to move in parallel due to spin correlation of Higgs boson decay products Excluded cross section together with expectations from SM Higgs production and alternative models. ee ee ℒ (pb -1 ) Total Background 0.7    0.1 (stat) Observed events 011 ee & e  combined

23 EPS2003, Aachen Nikos Varelas Future Prospects Near term: expect at least doubling of analyzed data for late summer conferences Long term: reaching 4-8 fb -1 by FY09 Detector upgrades for FY06 (Si, trigger) SUSY/Higgs Workshop: hep-ph/ Tevatron Higgs Sensitivity Group: June 24, 2003 WH  l bb ZH  bb Improvement due mainly to sophisticated analysis techniques

24 EPS2003, Aachen Nikos Varelas Summary Presented results from the first 50 pb -1 of Run II data New W and Z cross section measurements from 1.96 TeV shown First Tevatron combined W width results from Run II Results consistent with SM predictions Higgs studies are well under way Very exciting short and long term future prospects with a lot of hard work ahead