# Presentation: 506770

## Recent Electroweak & Top Physics Results From

- Recent Electroweak & Top Physics Results From

**Pushpa Bhat      Fermilab**

**DØ**

**DØ**

**DØ**

**Booster**

- Run II goal:  maximize integrated luminosity delivered to CDF & D0 ...

## ... with a program of upgrades throughout the complex

**Recycler Ring**

## Fermilab Run II Upgrades   

- Improved reliability and operating efficiency
- Optimization of transfers, improved optics and helices in Tevatron
- Increase pbar production, stack and store
- Upgrade Tevatron for higher bunch intensities

**Design Projection**
**  ****-  No schedule contingency, **
**    ****eng. design margin per subproject**
**Base Projection**
**  ****- ****Assumes schedule slip and **
**     ****under-perforance for **_**all**_** subprojects**
**      **

- Run II upgrades are handsomely
- paying off as evidenced by the
- Luminosity performance in FY04!

## Run II Luminosity History

**Instantaneous Luminosity Record : 1.1E32 cm****-2****sec****-1**
**Weekly Integrated Luminosity Record : 17.5 pb****-1**
**Integrated Luminosity delivered (Run II) = 670 pb****-1**

## DØ detector installed in the Collision Hall, January 2001

**DØ detector installed in the Collision Hall, January 2001**

## Upgraded Run II D Detector 

**Upgraded Run II D******** Detector **

- LAr/U Calorimeter, fine-grained, hermetic
- New trackers  Silicon, Scint Fibers
- 2T superconducting solenoid
- Pre-shower detectors
- Upgraded muon detectors
- Faster readout electronics
- New trigger & DAQ

**Total of  800,000 **
**Silicon channels **

**80,000 channels**
** ****in the Central Fiber Tracker**

## D Run II Luminosity 

- ~150-250 pb-1
- used for the
- reported analyses

## Electroweak Measurements 

- W, Z and di-boson Production
- W, Z important for calibration and understanding of the detector
- Tests of EW Standard Model and QCD
- Contained in signatures of many interesting physics processes
- Background to new particle searches
- The measurements reported here are the first steps of the Electroweak program at DØ in Run II
- W mass
- Important SM parameter
- Along with top mass, allows to Constrain Higgs mass
- (no results from D0 Run II yet)

## We, Zee Cross Sections

- Ldt= 177 pb-1
- Event Selection:
- W: ETe>25 GeV, |η|<1.05
- ET> 25 GeV
- 175572 candidates
- Z: ETe1,e2>25 GeV, |η|<1.05
- 1 electron track-matched
- 4712 candidates
- Main Bkgd.: QCD fake “e”

- MTe

- Mee

## Cross Section for Z/ 

- Ldt= 148 pb-1
- Event Selection:
-  pT1,2>15 GeV, M > 40 GeV
- ∑trks(pT)<3.5 GeV and in a cone of radius R=0.5 where R=√(∆η2+∆φ2)around each muon
- ∑cal_cells(ET)<2.5 GeV in a cone of radius R=0.4
- Cuts to remove cosmic ray background.

**14352 Candidate events**

- Bkgd.: bb (0.5±0.3)%, Z (0.5±0.1)%, W+Wx (0.2±0.1)%

## ZCross Section

- channels will be extremely useful for a lot of searches
- Ldt= 207 pb-1
- Event Selection:
- One   and the other decaying hadronically
- Isolated muon with pT>12 GeV
- Build NNs for 1 prong and 3 prong  hadronic taus
- 5- 10 GeV cut on had-tau ET
- |dφ|>2.5, NN>0.8
- 1946 events with ~55% bkgd.

- Data Points plotted are
- after background subtraction

- NN output

## Comparison of cross section

- measurements from Run I and
- Run II with SM predictions

## Measurement of WW Production

- Ldt= 224-252 pb-1
- Important because
- Tests trilinear couplings (WWZ, WW)
- SM background for many searches
- Signature for high mass Higgs
- Event Selection:
- Two high pT leptons of opposite charge; large missing ET
- Veto on Z and jet events, conversions

**Combination of ee, e********, ******** channels yield**

**Signal Significance**
**  ****=5.2 ******

**Theoretical Prediction (Campbell, Ellis) **
****** ****(WW) = 13.5 pb @ 1.96 TeV**

## ZWProduction

- Z Event Selection:
- Two high pT leptons, M(ll)>30 GeV
- Isolated photon, ET > 8 GeV and dR(, l)>0.7
- Photon ID eff= 82±2 %
- Main Background Z+jets production;
- estimated from data

- L.dt= 144 pb-1

**For E****T****(********) > 8 GeV**
**M(ll)>30 GeV**

- W : Ldt= 162 pb-1 (e channel), 82 pb-1 ( channel)
- Backgrounds: **W+jets, Jet faking ******
**Di-lepton events, e with no track; ****Z********W************ ******

- (ppWl+X)=
- 19.3 ± 6.7 ± 1.2(lum) pb

**Both Channels**

## The Top Quark

- Presently, Tevatron is the only source of top quarks!
- Dominantly pair-produced via strong interactions
- qqbar ttbar (85%)
- ggttbar (15%)
- Each top decays to a W boson and a b-quark nearly 100% of the time.

## Top Quark Decay Modes

**+ neutrinos in all cases except six jets mode**

- Depending on how the W’s decay,
- Top-antitop events have different
- final state signature

**W****+**

- 2 b-jets in each top-antitop
- event
-   b-tagging important

## Top Pair Production Cross Sectionlepton+jets Channels

**SVT**

**CSIP**

**SVT**

**Combining **
**e/******** +jets channels**
**and >=1 b-tag**
** ****samples**

**Single-tag**

**Double-tag**

- IP

**Build a multivariate discriminant using topological variables **
**Fit distributions of data to signal and backgrounds **

- Topological Analysis

- Using b-tagged events

******Ldt ~ 163 pb****-1**** **
**Two tagging algorithms**
- CSIP: a minimum number of tracks with large impact parameter significance
- SVT: secondary vertex with large decoy length significance

##  Top candidate +jets (2b-tags)

## Top Pair Production Cross Sectione+jets+b-tag Channels

**Combining 1 jet, >=2jets bins**

- Very small background <.1 evt
- Expected signal =3.22 evts

******Ldt= 158 pb****-1**

## Top e Candidate

- Soft lepton tag

- Isolated muon

- Secondary vertex

## Top Pair Production Cross Section 

## Top Mass Measurement

- Tevatron, Run I

## Top Mass MeasurementLepton+jets channel 

- Data Sample
- Event Selection
- e(+jets events with ETe (pT)>20 GeV, |η|<1.1 (2.0)
- Missing ET>20 (17) GeV
- 3 jets with ET>20 GeV, 4th jet ET>15 GeV, |η|<2.5
- Fit 2<10. for top-antitop decay hypothesis
**Number of events passing the selection criteria and the estimated composition **

| Channel | e+jets | +jets |
| --- | --- | --- |
| No. of Events | 101 | 90 |
| Sample Composition   tt
                         W+jets
                         Multijets | 30.9
65.7
4.4 | 29.9
53.4
6.9 |

******Ldt= 160 pb****-1**

## The S/B Low-Bias Discriminant (D)

- The variables
- Missing ET
-  Aplanarity = 3/2 x smallest eigenvalue of P
- HT2 = (HT – ETjet1)/H||
- K’Tmin= (min of 6 ∆Rij). ETmin/ ETL

**D****  ******

**All events**

**B-tagged**
** ****events**

**Fitted mass ******

## Top Mass Measurement Lepton+jets channel 

- Extraction of mass information
- The Ideogram Method
- The likelihood to observe a given event is written as,
-    where Pevt is the probability for the event to be a signal event
-    G: the Gaussian resolution function
-    BW: expected Breit-Wigner distribution
-           of the average of the two reconstructed
-           top masses for a given top mass mt
- Combined Likelihood for the sample:

- e/ +jets data results in 

## Top Mass Measurement (contd.)

- Extraction of mass information
- Template Method
-     Compare the fitted mass (the smallest 2  solution)                 distribution for data with the templates from signal Monte carlo at different possible top masses and background.
- Additional Cuts:
- ETW= | pTl|+|ET|>65 GeV
-  HT2>90 GeV, D >0.4
-      87 events in data
- A log likelihood fit to
-     e/ +jets data yields

## Single Top Quark Production

|  | 95% C.L. limits |
| --- | --- |
| s-channel) | <19pb |
| t-channel) | <25pb |
| s+t channels) | <23pb |

**Need about 1 fb****-1**
**for observation**

- EW production of top quark    direct probe of |Vtb|

******Ldt~163 pb****-1**

- Signature:
-  high pT lepton, large Missing ET
-   ≥ 2 jets (≥ 1 b-jet)
- Backgrounds:
- W/Z+jets, top-antitop,  QCD,

## Summary

- Fermilab Accelerator Run II upgrades are providing continually improving luminosity performance.
- Peak luminosity record >1E32 cm-2sec-1
- Weekly integrated luminosity record =17.5 pb-1
- Through 2009: Expect 4-8 fb-1
- Important electroweak results are emerging
-  channels being exploited and added
- Precision measurements in top physics have begun
- With 2 fb-1
- W mass uncertainty ~ 30 MeV
- Top pair cross section uncertainty ≤ 10%
- Top mass with ~2 GeV error
- Vtb using single top process with 10% precision
- Hints of new physics?
- A rich harvest of physics with > 4 fb-1
- Who knows what we will find?

## Back-up Slides

## b-tagging

- We have developed two independent tagging algorithms, together with multiple ways of verifying their efficiencies

**Efficiency ~ 50%**
**Mistag rate **
**(light quark jets) ~ 1-1.5%**

**Top candidate event**tagged by bothalgorithms
- Run 169923 event 16396718Electron pT = 27 GeV , Missing ET = 58 GeV, 4 jets with pT(jet) = 51, 36, 30, 53 GeV ; HT = 207 GeV

## Tracking Performance

**Impact Parameter Resolution**

**B****±**** ******** J/******** K****±**

## Top Pair Production Cross Sectionlepton+jets+b-tag Channels

- Top Pair Production Cross Sectionlepton+jets+b-tag Channels

**CSIP**

**SVT**

**CSIP**

**SVT**

**Combining **
**Both channels**
**and >=1 b-tag**
** ****samples**

**Single-tag**

**Single-tag**

**Double-tag**

**Double-tag**

**CSIP tag**
- S = IP/(IP)
-     2 tracks with S>3
-     or 3 tracks with S>2

**SVT tag**
**Lxy/********(Lxy)>7.**

- IP

## Is Top to Wb vertex SM? W Helicity

- In SM *F*-=0.30, *F*0 =0.70, *F*+ =0

- Helicity of W manifests itself in
-  decay product kinematics

- DØ (l+jets, 160 pb-1)

- No deviations from SM predictions

*F*+ < 0.24 at 90% C.L.
- 	topological
*F*+ < 0.24 at 90% C.L.
- 	b-tagging

- Test of V-A coupling in top decays: W couples only to LH particles
- This together with angular momentum conservation allows top decays into LH
- (negative helicity) or longitudinally-polarized (0 helicity) W bosons