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24 April 2003 - DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 1 Alan L. Stone Louisiana Tech University Louisiana Tech University.

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Presentation on theme: "24 April 2003 - DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 1 Alan L. Stone Louisiana Tech University Louisiana Tech University."— Presentation transcript:

1 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 1 Alan L. Stone Louisiana Tech University Louisiana Tech University … on behalf of the DØ Collaboration Recent Results on Electroweak & Related Physics at DØ • Introduction & Motivation  W/Z 0 muons  W/Z 0 electrons  Z ’ (ee) Search • Top Quark Cross Section • Conclusions

2 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 2 Motivation for Measuring W & Z Production • Test of SM couplings • Constrain proton PDFs • Probe effects of NLO QCD corrections • Better understanding of our Experiment –Efficiencies, Backgrounds, Luminosity –Use these signals to tune triggers & algorithms • Improved luminosity measurement –With sufficiently small statistical & systematic uncertainties –Normalize to other measurements • Preliminaries to other Run II goals –W boson mass –Precision EW measurements –Top Quark Studies –(W or Z) + Higgs DØ Run IIa Prediction Previous Tevatron results

3 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 3 W and Z Production Mechanics p q q p W(Z) l (l) Distinctive lepton decay event signatures  High P T isolated leptons (e or  ) • One high P T lepton + Missing E T (W) • Two high P T leptons (Z) Cross Sections increase by ~10% from 1.8 to 1.96 TeV W  l  ~1 L = 2  O(a s 0 )

4 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 4 W & Z Cross Sections: A Counting Experiment Measurements make use of data taken from mid-August ’ 02 through mid-January ‘ 03 Integrated Luminosity Backgrounds Acceptance from Monte Carlo Efficiencies from data where possible

5 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 5 The DØ Run II Detector SMT •Builds on the firm foundation of the Run I calorimeter & central muon system •Added magnetic tracking, silicon, new forward muon system, new electronics •Electroweak analyses make use of the full detector capabilities

6 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 6 The Muon Detector • Two regions & Three layers of Scintillators and Drift Tubes –Central and Forward  A – inside toroid magnet  B & C – outside toroid magnet • Muon rapidity coverage to ±2 • Shielding reduces backgrounds by x Mini drift tube Plane and Pixels (10m  10m)

7 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 7 Z 0  Event Selection Event selection  2 tracked, oppositely-charged  ’ s  p T >15 GeV & |  |<1.8 • Di-muon trigger • At least one muon is isolated  (  R) 2 =(    2 +(    2 >4.0  |  t| < 9 ns in scintillator • NO explicit mass requirement Background is small  Z 0 bbar is 1  1%  Z 0  is 0.5  0.1% P T (  1 )=40.97 GeV P T (  2 )=43.92 GeV M(  )=86.04 GeV

8 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 8 Z 0  Efficiencies mcontrol mprobe L1+ L 2 central track L1 O R no L1 Z • Acceptance from MC (40±1%) • Efficiencies from data tra c k OR no track  L1 = 87±2%   ID = 91±1%  trk = 82±1% (scaled)

9 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 9 Z 0  Cross Section Drell-Yan Contribution  Correct for 12  1% due to photon exchange and photon-Z interference determined from Pythia 1585 Candidates

10 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 10 W 0  Event Selection Offline • One isolated muon matched with central track p T >20 GeV  In fiducial region of the trigger: |  |<1.6 • Muon corrected Missing transverse energy > 20 GeV  No second muon in event (veto Z 0  events) Trigger • L1: Scintillator based single muon trigger (no p T cut) • L2: At least one muon with p T >5 GeV • L3: At least one track with p T >10 GeV P T (  )=37.48 GeV ME T =35.5 GeV

11 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 11 W 0  Cross Section 7352 Candidates in Backgrounds  Z 0 bb, b 0  where  passes isolation cut ¥ 5.8%, subtracted from above distributions  Z 0  : ~9%  W 0  0  : 3.6% • QCD estimated from data

12 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 12 • Liquid argon sampling ¥Stable, uniform response, rad. hard ¥LAr purity important (< 0.7 ppm O 2 equivalent) • Uranium absorber (Cu/Fe for coarse hadronic) ¥dense absorber hence can be compact ¥Nearly compensated EM and hadronic response ¥Linear response • Hermetic with full coverage   < 4.2 (   2 o )   int  total) Z y x   The Calorimeter

13 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 13 Electrons • Isolated EM Cluster in the Calorimeter • E T > 25 GeV with large EM fraction • Shower shape consistent with MC expectation Z 0 ee • 70 GeV < m ee < 110 GeV W 0 e • Missing transverse energy > 25 GeV • Matched with central tracks Trigger: • L1: 1 calorimeter tower > 10 GeV (or 2 > 5 GeV) • L3: Electron candidate > 20 GeV, shower shape cut P T (e)=40.5 GeV ME T =43.2 GeV M T (W)=83.7 GeV W/Z 0 e Event Selection e+e+

14 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 14 Z 0 ee Cross Section 1139 Candidates in M e+e- (GeV) D0 Run II Preliminary Drell-Yan Contribution •Small effect (1.7%) in the mass window of 70 < m ee < 110 GeV QCD Background •Determined from data by fitting signal and background shape Efficiencies per electron • Trigger: 98±2% • EMF, isolation: ~100% • Shower shape: 86±1% • Track Matching: 73±2%

15 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 15 W 0 e Backgrounds • Dominant background from QCD multijet events • Estimated from data tight = loose + track match Other backgrounds:  W 0  0 e (1.5 %, MC)  Z 0 ee (very small) From QCD dijet sample loose tight 2.3+/-1% D0 Run II Preliminary ME T (GeV)p T (GeV) N loose = N W + N b N tight = N W  trk + N b  f Solve for N W

16 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 16 W 0 e Cross Section Candidates in Background subtracted distributions compared to MC Pythia

17 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 17 Results C. R. Hamberg, W.L. van Neerven and T. Matsuura, Nucl. Phys. B359 (1991) 343 CTEQ4M PDF ZW

18 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 18 Direct Search for Z'  ee M(ee) around the Z 4585 Candidates in Data Bkg (QCD+DY/Z) Bkg (QCD only) 10x Z'(600GeV) Backgrounds Drell-Yan dominates M ee <150 GeV • Estimated from Pythia (CTEQ4L) QCD dominates M ee >150 GeV • Fake electrons from jets • Real electrons from heavy flavor • Estimated from data D0 Run II Preliminary •Search for Non-SM heavy particles that decay to lepton pairs –Assumes Z' couples as Z •Previous Tevatron Run I Limit –M Z' >690 GeV •Event Selection –2 isolated EM objects  |  |<1.1 or 1.5<|  |<2.5 •E T >25 GeV –No track requirement necessary M e+e- (GeV)

19 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 19 Z ’ Search M(ee)=489.1 GeV  Form limit from the ratio of cross sections for (  B) Z' /(  B) Z where many of the systematic errors in the efficiencies and luminosity measurements cancel • Applied a binned likelihood approach with Poisson statistics • Remaining Uncertainties –K-factor 5%  A z ’ /A z & PDFs 2-3% D0 Run II Preliminary

20 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 20 p p t b WW q q’q’ t b W+W+ ll X Production cross-section Resonance production Production kinematics Top Spin Polarization Top Mass W helicity |V tb | Branching Ratios Rare/non SM Decays Anomalous Couplings CP violation Top Spin Top Charge Top Width _ _ _ _ Run I: Discovery   tt ¥Top mass ¥W helicity in top events ¥tt spin correlations ¥Top p T ¥Searches for new physics (X  tt and top decay) Run II: With high precision we hope to answer questions such as: ¥Why is top so heavy? ¥Is it or the third generation special? ¥Is top involved with EWSB? ¥Is it connected to new physics? Motivation for Measuring Top Quark Production

21 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 21 Top Quark Production Mechanics • At the Tevatron, top quarks are produced in pairs –Br(t?Wb)=100% Lepton+jets (topological) Lepton+jets (soft muon tag) dileptons e+jets,  +jetse+jets/ ,  +jets/  ee, e ,  Br = 14.7% Br = 2.5 and 1.2% Efficient Not very pure Pure Not very efficient Pure and efficient Low branching Run I Results ~100 top events  Prediction of ~30%  tt cross section increase from Run I (1.8 TeV) to Run II (1.96 TeV)

22 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 22 -- jet e+e+ 91 GeVETET P T = 55.2j P T = 141.0j P T = 58.1  P T = 20.3e+ Di-muon mass (GeV)  (tt  ll+jets) Event Selection ETET E T (GeV) Event Selection  Two high p T isolated  or e ¥ E T (Z mass) cut  ? 2 jets, E T >20 GeV & |  | < 2.5  H T =  (E l T,E jet T ) cut Backgrounds ¥ WW, Z? tt determined with MC ¥ Z/g*, W+jets and QCD from data 0.3 ± 0.02Expected Signal 0.59 ± 0.30All BG 0.89 ± 0.30All 0.18 ± 0.084QCD+W+jets 0.40 ± ± ± Z?  Z?  ?  WW?  2Observed N events Process  +jets D0 Run II Preliminary

23 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University ± ± ± ± ±0.01Expected Signal 0.07 ± 0.01All BG ± 0.01 Z?ll DY?ll QCD,W+jets 0.02 ± ± Z?tt?ll WW?ll 1Observed 0.02 ± ± ± ± ± ± ± ± ee ee Jet 1 Jet 2  (tt  ll+jets) Results D0 Run II Preliminary e  +jets Jet Multiplicity Sum of jet, electron P T (GeV)

24 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 24  (tt  l+jets) Event Selection (no  tag) Scaling: # of W for N jets ? 4 jets Procedure  Preselect a sample rich in W ’ s • Evaluate QCD multi-jet (as f [Njets] ) • Estimate W+4 jets assuming Berends Scaling • Apply topological selection Event Selection • Isolated lepton w/ P T >20 GeV • ME T > 20 GeV  4+ jets with E T >15 GeV & |  |<2.0 (2.5) • Soft non-isolated muon tag veto Backgrounds ¥ multijet evaluated from data vs. N jets  e+jets: due to fake jets (real  o and  )   +jets: due to heavy flavor decays ¥ Estimate real W+4 jets with scaling law D0 Run II Preliminary  Estimation of QCD Background

25 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 25  (tt  l+jets) Results (no  tag) 4 4 N obs    0.9  +jets    0.5 e+jets Exp Signal* Bkg. Total N QCD NWNW Analysis Topological Selection •1+ jet with E T >55 GeV •ME T Cal>15 GeV  |  W | 60 GeV •H T (jets & W)>220 GeV •H T >180 GeV •Aplanarity(W-jets)>0.065  +jets Candidate Event  - Jet 1 Jet 2 Jet 4 Jet 5 Jet 3  +jets Candidate Event * For  = 7pb

26 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 26  (tt  l+jets) Event Selection (soft  tag) Preselection criteria • Same as leptons + jets except soft non- isolated muon is not vetoed  3+ jets with E T >20 GeV & |  |<2.0 • Aplanarity > 0.04 • H T >110 GeV Soft Muon Tag  p T (  )>4 GeV within  R<0.5 of a jet Sig.* 0 2 N obs 0.6  0.3  +jets 0.2  0.1 e+jets Bkg. Tot. Analysis * For  = 7pb D0 Run II Preliminary 27 e+jets events 23  +jets events

27 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 27  (tt  X) Cross Section Combined

28 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 28 Conclusions  Combining the observation of the top decay channels an excess of 3  is observed, compatible with a signal expectation at the 35% CL  Four new W & Z cross section measurements:  Assuming same SM Z couplings to quarks and leptons, Z' is excluded at 95% CL at m Z' <620 GeV

29 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 29 Backup Slides

30 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 30 Z  ee Candidate No centrally matched track to second electron P T (e 1 )=45.1 GeV P T (e 2 )=40.1 GeV M(ee)=85.1 GeV

31 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 31 W 0  Backgrounds Background estimated from data. Dominant background:  bbar, b0  events where the muon passes isolation cuts

32 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 32 W 0  Efficiencies • Dimuon events  1  w/central track match  1 Calorimeter  • Determine fraction of Calorimeter muons that meet local muon criteria L1 Trigger efficiencies Muon reconstruction efficiency = N 1 /(N 0 +N 1 ) = 74±2% N 0 = 1 local  + 1 cal  N 1 = 2 local  's L2L3

33 24 April DIS03 - St. Petersburg, RussiaAlan L. Stone - Louisiana Tech University 33 Uncertainties Z  W  Z/W  e


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