1. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20051 Top Quark Production Cross- Section at the Tevatron Collider On behalf of DØ & CDF Collaboration KIRTI RANJAN UNIVERSITY OF DELHI, INDIA & FERMILAB

2. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20052 OVERVIEW  Motivation  Tevatron Run II & Detectors  Top quark production & decay  Results  Top pair production  Dilepton  lepton + Jet  All Jets  Single top production  Summary NEW

3. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20053  Discovered by DØ & CDF in 1995  Studied with limited Run I statistics!  Role in the Standard Model (SM)  m top ~ 175 GeV : Heaviest elementary particle  Top quark mass ~ EWSB scale  Short lifetime (~ 10 -24 s) – properties of bare quark  Accurate measurement of top mass constrains Higgs mass  Sensitive to physics beyond the SM  Look for non-SM production or decay modes  Possible background for New Physics searches MOTIVATION It’s FUN studying TOP ! TEVATRON is THE only TOP FACTORY till LHC starts operating

4. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20054 TEVATRON RUN II Tevatron is performing extremely well ! Both experiments have accumulated ~ 680 pb -1 of Data Results presented here ~ 150 – 350 pb -1 L PEAK > 1*10 32 cm -2 s -1 Design Base Present status

5. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20055 EM Hadronic CDF Muon system Tracker DETECTORS Coarse Hadronic (Tail catcher) Fine Hadronic EM DØ Muon system Magnetized iron Tracker  New Silicon Detector  New Central Drift Chamber  New End Plug Calorimetry  Extended muon coverage  Faster DAQ  New Silicon Detector and Central Fiber Tracker in a 2T solenoid  Substantially upgraded muon system  Faster DAQ

6. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20056 TOP QUARK PAIR PRODUCTION & DECAY  Strong Production  At Tevatron energies ( = 1.96 TeV) : primarily produced in pairs SM Prediction (at m top = 175 GeV) Dominant Uncertainties: PDF( 7%) & Scales ( 5%) Role reversed at LHC! RUN I ( = 1.8 TeV) Results CDF: DØ : ( Cacciari et. al,. JHEP 0404:068,2004 ) x-section ~ 30% higher than Run I ( = 1.80 TeV → 1.96 TeV) Gluon Fusion Annihilation  In SM, BR (t → W b) ~ 100%  Final states are determined by W decay modes

7. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20057 FINAL STAES 20% 14.6% 1.2%2.4% 46% 1.2% Requires good identification of e, , jets, & Missing E T LEPTON+JETS [ e,  + 4 jets (2 b jets) ]  Large BR ~ 30%  Moderate background ALL HADRONIC [ 6 jets (2 b jets) ]  Largest BR ~ 46%  Largest background DILEPTON [ ee, , e ,+ 2 b jets ]  Small BR ~ 5%  Smallest background Golden Mode

8. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20058 DILEPTON Signal Selection :  Two high P T Leptons  Two high P T Jets  Large One lepton & One oppositely charged track Final cut Two Oppositely charged leptons Final cut Background dominated Background :  Physics (from MC) : Z /  * → , Dibosons  Instrumental (from Data): fake, fake Leptons CDF: 200 pb -1 DØ : 150 pb -1 ( PRL 93, 142001, 2004) DØ Run II preliminary (150pb -1 ) Two Oppositely charged leptons

9. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 20059 DILEPTON  CDF : Loose cuts to increase no. of signal events  Fit N JET vs. distributions for physics backgrounds CDF Preliminary 200 pb -1 CDF: 200 pb -1

10. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200510 Signal selection  One high P T Lepton  Multiple high P T Jets  Large LEPTON + JETS (TOPOLOGICAL)  Strategy : Extract signal from kinematic / topological characteristics of the events & use Neural Net (CDF) / construct Likelihood discriminant (DØ) Backgrounds  Physics : W+Jets  Instrumental: QCD Multijet DØ : 230 pb -1 : CDF: 347 pb -1 : (hep-ex / 0504043) DØ RunII Preliminary 230 pb -1 ≥ 4jets NEW 38% 44% 18% 167 events

11. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200511 B Mesons are Massive & long-lived (Lifetime Tagging)  Displaced track vertices : SVT (DØ) SVX (CDF) Semi-leptonic decay of B-Mesons (Soft Lepton Tag or SLT)  Identify low-p T e /  inside jet  b-jets provide extra handle to identify Top quark ‘b’ JET IDENTIFICATION ~ 60 % ← event tagging efficiency → ~ 15 % ~ 0.5 % ← Light-flavor jet mistag rate → ~ 4 %

12. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200512 DØ : 230 pb -1 : SVT : LEPTON + JETS (b-TAGGING)  DØ : SVT Analysis NEW = 1 Tag ≥ 2 Tags = 1 Tag 4th Jet bin ≥ 2 Tags 4th Jet bin

13. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200513  CDF : Soft  Tag & SVX Tagging Soft  Tag CDF : 194 pb -1 : Soft  Tag : LEPTON + JETS (b-TAGGING) CDF : 318 pb -1 : Single Tag : CDF : 318 pb -1 : Double Tag : NEW ≥ 1 Tag ≥ 2 Tags NEW

14. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200514 ALL HADRONIC  Increase signal significance using both topological Cuts & b-tagging  small S/B ~ 0.2 - 0.3 CDF: 165 pb -1 : DØ : 160 pb -1 : 6 ≤ N JET ≤8 Signal selection  Multiple ( ≥ 6 ) high P T Jets Backgrounds  Huge QCD multijet background

15. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200515 X-SECTION SUMMARY

16. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200516  Electroweak Production  Not yet observed !  Main production mechanisms  ~ 40% of the x-section Direct measurement of |V tb | Sensitive to physics beyond the SM SINGLE TOP QUARK PRODUCTION SM Prediction :  s ~ 0.88 pb,  t ~ 1.98pb (Harris et al., PRD 66, 054024, 2002) RUN I RESULTS (~100pb -1 ) CDF:  s < 18 pb,  t < 13pb,  st < 14pb DØ :  s < 17 pb,  t < 22pb  Signal Signature  Same as Lepton + Jets ( ≥ 1 b jet) but with lower jet multiplicity (using Leptonic decay of W)  Background , W+jets, QCD multijets  Analysis Strategy  Maximize acceptance  Sophisticated methods to separate signal from background

17. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200517 SINGLE TOP QUARK PRODUCTION 162 pb -1 @ 95% CL Combined : W+2jets ( ≥1 b jet); 140 ≤ M l b ≤ 210 GeV Channel specific : exactly 1 b-jet (t-channel) or 2 b-jets (s-channel) ( PRD 71, 012005, 2005 )

18. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200518 SINGLE TOP QUARK PRODUCTION  Separate signal from background 2 ≤ N JET ≤ 4; ≥ 1 b-jet; ≥ 1 non-b jet in t-channel  Cut based → Event Counting  Decision Tree  Neural Network binned likelihood calculation NEW 230 pb -1 @ 95% CL Cut based Decision Tree Neural Network NEW WORLD’S BEST LIMIT : improvement by a factor of ~2 NEW

19. KIRTI RANJANDIS, Madison, Wisconsin, April 28, 200519  Tevatron is performing remarkably well  Top quark pair production  Measurements in different channels providing consistent results with the SM  b-tagging has provided a powerful handle to identify top quark  With more data, x-section measurement is getting dominated by systematic uncertainties  Working very hard towards reducing systematics  Single Top quark production  New world’s best limit on x-sections  Observation expected with ~ 1 – 2 fb -1 of Data  Analyses refinement continues  Analysis with more data is on the way OUTLOOK Top Quark: A Journey from Discovery → Precision has begun! SM