# Presentation: 929796

## ICHEP 2002, Amsterdam                              	                  July 23 - 31, 2002

**Top Quark Physics at the Tevatron**
- Ia Iashvili
- University of California, Riverside
**For the CDF and DØ Collaborations**
- Introduction
- Latest results from Run 1
- New results from Run 2
- Summary and prospects

## Introduction

**Top quark has a special place in the SM**
- The Yukawa coupling,
- Special role in EW symmetry breaking?
**Discovered at  Tevatron in 1995**
- CDF,  PRL 74, 2626 (1995)
- DØ,    PRL 74, 2632 (1995)
**Top quarks have been observed in pair production through strong interaction**:

**3 classes of signal in       production**:
- Dilepton — 2 high-PT  leptons,  2 b-jets, large  ETmiss  —  BR(ee , , e) = 5%
- Lepton+Jets  —1 high-PT lepton, 4jets (2b’s), large  ETmiss — BR(e,+jets) =30%
- All-hadronic   — 6 jets (2b’s) — BR=44%
**Another mechanism  —   single-top production via  EW interaction**:
**Wealth of information extracted with   ****~100 ****      events per experiment  based on  ****~110 pb****-1****  Run1 data**

- Ia Iashvili

- ICHEP 2002

## Top Physics in Run 1

-        **Xsection and top mass**
- CDF:                                                        *(Phys.Rev.D64 03022, 2001)*
- DØ:                      *(hep-ex/0205019,2002)*
- CDF+ DØ:                                                *(Fermilab-TM-2084, 1999)*
- in good agreement with theory

- CDF l+jets
- 76 events

- Ia Iashvili

- ICHEP 2002

## Top Physics in Run 1

**Studied top-antitop spin correlation using   6 dilepton events**** ****(DØ, ***Phys.Rev.Lett. 85, 256,2000***):**
- SM:**   **K ~ 0.9
- DØ :** **** **K > -0.25 at 68% C.L.
**Branching ratio R=BR(t********Wb)/BR(t********Wq)     and |V****tb****|**** ****(CDF, ***Phys.Rev.Lett.86, 3233, 2001***):**

**W helicity in top decays using dilepton and lepton+jets sample**** ****(CDF, ***Phys.Rev.Lett. 84, 216, 2000***):**
- SM:
- CDF:
**Top quark P****T**** distribution****                       ****(CDF, ***Phys.Rev.Lett. 87, 102001, 2001****;*****  DØ, ***Phys.Rev.D58, 052001,1998***)**
**All measurements in agreement with the Standard Model**

- Ia Iashvili

- ICHEP 2002

## Search for single top production in Run 1

**CDF has also performed search for two single-top processes combined. Derived Xsection limit is: **
-  ****** ****(single-t) < 14 pb at 95% C.L.****  **(*Phys.Rev.D65, 091102, 2002*)** **

**Search for single top production in Run 1**

**At Tevatron dominant single top production processes are:**
**Final state consists of W decay products plus  jet(s) :**
- Searches are restricted to leptonicaly decaying W  e, 
**Single top processes are harder to observe than       production:**
-  final states containing fewer jets suffer from a larger background
- A priori no sensitivity expected in Run I data, unless new physics processes enhance production rate

- Ia Iashvili

- ICHEP 2002

## Search for single top production in Run 1

**CDF: single-tag W+2jets events**

**CDF: double-tag W+2jets events**

**To separate two single-top processes consider non-overlapping W+2jets samples:**
-  single-tag events -- dominated by t-channel
-  double-tag events -- dominated by s-channel
**In t-channel light-quark often is in the same hemisphere as the (anti)proton when (anti)top is produced**
**In double-tag events use M****l********b ****distribution to extract s-channel contribution**** **
**95% C.L. limits are set by CDF at:******
** ********(s-channel) < 18 pb**
-  ******(t-channel) < 13 pb               **(*Phys.Rev.D65, 091102, 2002*)** **
**95% C.L. limits derived by ****DØ:**
-  ******(s-channel) < 17 pb**
-  ******(t-channel) < 22 pb               **(*Phys.Lett.B517, 282, 2001*)** **

- Ia Iashvili

- ICHEP 2002

## Search for       resonances in Run 1

**Search for       resonances in Run 1**

**Models with dynamically broken EW symmetry**** ( ****“Technicolor”)**** ****predict  existence of top quark condensate X that can decay to       pair,**
**Search for narrow                  resonance** — reduce sensitivity  to the model details

**Use lepton + jets events.** Fit observed distribution of           to derive probability distributions of Nevents for signal,  top pair,    and other SM background processes.

- Ia Iashvili

- ICHEP 2002

## Search for       resonances in Run I

-  **No statistically significant excess has been observed and therefore 95% C.L. limit has been derived  on production Xsection assuming ********x****=0.012M****x ****and M****t****=175GeV**

-  **For particular model of leptophobic topcolor** (*C.T.Hill and S.Parke, hep-ph/9911288*) **DØ excludes**** ****M****x****< 585 GeV at 95% C.L. **(*hep-ex/0205019*)
-  **Under the same assumption CDF has set lower limit of**** ****480 GeV at 95% C.L. ** (*Phys.Rev.Lett.85,2062,2000*)

- Ia Iashvili

- ICHEP 2002

## Tevatron Upgrade

**New Main Injector and Recycler Ring**
**Improved Antiproton source and Booster**
- Increase pbar yield
- Increase luminosity
**Increase number of bunches**
- Reduce number of interactions per crossing
- Reduce  bunch spacing

**Increase beam energy 900********980GeV**
- Increase Xsections for interesting physics processes, e.g. by 30-40% for top production:
-          - from ~5 to ~7 pb for top pair,
-          - from ~2.4 to ~3 pb for single top

-  Run 1  Run 2a  Run 2b
- 0.1 fb-1    2 fb-1   15 fb-1

**Run2 data taking started in spring 2001**

- Ia Iashvili

- ICHEP 2002

## Run 2 detectors

**CDF upgrades**
- New Silicon Vertex Detector (SVX) and faster tracking drift chamber (COT)
- New scintillating tile end-plug calorimeters
- Increased  coverage for muon detectors
- New scintillator time of flight system
**DØ upgrades**
- New Silicon (SMT) and Fiber (CFT) trackers, placed in 2 T magnetic field
- Calorimeter supplemented with the preshower detectors
- Significantly improved muon system
**Entirely new DAQ and trigger systems to handle high event rate**
**Both CDF and DØ will replace Silicon detectors during 2004 shutdown — dictated by radiation damage.**

**CDF**

**DØ**

**Both detectors: **
**- b-tagging capability through  displaced vertices**
**- Improved lepton identification systems**

- Ia Iashvili

- ICHEP 2002

## W  e candidates in Run 2 DØ data

**W ** e** candidates in Run 2 DØ data**

-  **W+jets and Z+jets are primary  backgrounds  to top ********  Study these processes to asses  detector performance before enough top  events are detected**
-  **W  transverse mass spectrum in                  e + missing E****T**** inclusive sample. QCD background derived from the data**

-  **Inclusive jet multiplicity in background**
**subtructed  W********e******** sample — follows**
**to linear in log law (Berends scaling)**
-  **With higher statistics and b-tagging **
**requirement, enhancement at W+4jets**
**will indicate  ttbar********e********j+jjj contribution**

***L***int~7pb-1

- Ia Iashvili

- ICHEP 2002

## W and Top candidates in Run 2 CDF data

- W events: Ntracks associated to 

-                W events

- Ia Iashvili

- ICHEP 2002

## Z candidates in Run 2 data

-         Z e+e- events

-           Z +- events

**  ****DØ **

- Ia Iashvili

- ICHEP 2002

## 
b-tagging capability important to suppress background to top (W/Z+jets, QCD jets)

To tag b-jets exploit  both techniques:
a)  soft lepton tagging (SLT);       b) tagging with displaced vertices

**b-tagging capability important to suppress background to top (W/Z+jets, QCD jets)**
**To tag b-jets exploit  both techniques:**
- a)  soft lepton tagging (SLT);       b) tagging with displaced vertices

**b-tagging in Run 2**

**Impact  Parameter Tagging:**
- study  di-jet events with and without muon
- di-jet event containing muon within     dR <0.7 and PTrel>1.5 GeV  are enhanced in heavy flavour

**Soft Lepton Tagging****:**
- B(blc)~20%,  B(bc  ls)~ 20%     with l=e and 
- use both muons and electrons looking at PT relative to jet axis
- Muon tagging has been checked in data for bbbar decay studies

- ~resolution

- Ia Iashvili

- ICHEP 2002

## b-tagging in Run 2

**b-tagging in Run 2**

**Current performance is approaching Run 2a design figure for both CDF and ****DØ**

**unfolding beam width of 30 ± 3 ********m**

**Expected :**
******=11********m**

-      **CDF**

-   **DØ**** **

**B lifetime **
**using J/******

- Ia Iashvili

- ICHEP 2002

## Projection on measurement precisions

**Projection on measurement precisions**

**Two largest systematic errors in M****t**** are due to****            ****Jet Energy Scale (JES) ****and ****gluon radiation**
**In Run2, Z******** bb decays will be used to limit JES — relies on L2 Silicon Track Trigger**
**Gluon radiation correction will be constrained  by comparing double-tag events with MC simulation **
**Expected accuracies by the end of Run2b :****               ****Top mass ~ 1.4 GeV, W  mass ~ 16 MeV.  ****Gives ****         ****indirect constraint on higgs mass****  ********M****h****/M****h**** ~25%   ***(hep-ph/0202001, Snowmass Working Group  on  Precision EW measurements)*

- Tevatron
-  projection

- Ia Iashvili

- ICHEP 2002

## Summary

- Successful top quark physics program at Run 1
- All measurements consistent with the Standard Model
- But limited in statistics
- We are entering exciting era of Run 2. Performance of upgraded CDF and DØ detectors are already close to expectations — many improvements relevant to top physics
- Tevatron Run 2 will allow to precisely measure top quark properties. Signs of new physics could well show up first in these measurements.

- Ia Iashvili

- ICHEP 2002