# Presentation: 197987

## Electroweak Measurements at the Tevatron

**Cairo International Conference on HEP**
**January 9, 2001**
**Results from D0 and CDF’s Run I**
**Prospects for the 1st 2 fb****-1**** of Run II**

**Tom Diehl**
**Fermi National Accelerator Laboratory**
**Batavia, Illinois**

## Acknowledgements

- Thanks as always to D0 and CDF collaborations.
- Some material in this talk comes from previous presentations by
- Uli Heintz, Meena Narain, Georg Steinbruck, John Butler, Natalia Sotnikova, and Darien Wood.

## Electroweak Measurements at the Tevatron

- Introduction
- W and Z Boson Properties
- General Features of Production
- Inclusive Cross Section
- W Boson Width &  Mass
- Trilinear Gauge Boson Couplings
- Top Quark Properties
- General Features
- Top Pair Production Cross Section & Production Dynamics
- Top Quark Mass
- Branching Ratios & Rare Decays
- Electroweak Top Quark Production
- Standard Model Higgs Boson
- M(top), M(W), and M(Higgs)
- Standard Model Higgs Boson Search

- Run 1 Results and
- Prospects for Run II

## The Run 1 D0 Detector

**The Run 1 D0 Detector**

- Electroweak analyses use all of the detector capability

**Non-magnetic central tracking and no silicon detector**

**Calorimeter  **Hermetic 
- x x
- EM)=15%/E1/2
- had)=50%/E1/2

**Large muon toroids**
- pp
- p in GeV/c

## Run 1 CDF Detector 

**Calorimeter:**
- EM)=15%/E1/2
- had)=50%/E1/2

**Magnetic central tracking w/ large radius & a silicon detector for vertices**

**Muon detector provides ID. Momentum measurement from central tracker**

## D0 Upgrade

## CDF Upgrade

## W/Z Physics 

**W/Z Physics **

- Topics
- General Features of Production
- Inclusive Cross Section
- W Boson Width
- W Boson  Mass Preliminaries
- W Boson Mass
- Trilinear Gauge Boson Couplings

- W Bosons Detected:

## General Features of W and Z Production

**General Features of W and Z Production**

**Notes:**
 Production dominated by qq annihilation
 Due to very large pp jj production, need to use leptonic decays
 W  l (BR ~ 11% per mode)	
 Z  ll (BR ~ 3% per mode)
 Distinctive event signatures 
 High PT isolated leptons (e or )
 One high PT lepton + Missing  ET (W)
 Two high PT leptons (Z)
 Low backgrounds
 Large samples
 Well understood EW vertex 
 Test QCD 

##          Inclusive Cross Section

- Luminosity:
- L(D0) = 1.062 x L(CDF)
- D0 uses world avg. (pp)inel,
- CDF uses CDF measurement

** **B(W****l ) ~ 2.2 nb
-  B(Z****l+ l-) ~ 0.22 nb
- Cross section measurement uncertainty:
- Stat  Sys ~ 2%,
- Luminosity error ~ 4%
- Theory prediction uncertainty:
-  ~ 3%, NNLO, O(s2)
- Dominated by PDF’s at NLO...
- (need NNLO)

**         ****Inclusive Cross Section**

## W Boson Width

- Indirect Method

- Direct Method (CDF)
- Model independent
- Study high-end tail of MT(l).

**(SM:2.093 ********0.002)**

- Form ratio:

**LEP**

**Perturbative**
**QCD**

**SM EW**

- CDF+D0 combined

**(LEP combined:2.12 ********0.11)**

## W Boson Mass Preliminaries

- Input from theorist’s calculations tuned by our measurements.

- PT(W) Ladinsky-Yuan

- W Spin Orientation
- E. Mirkes.  (1992)

- PDF’s

- W Boson Production
- & Decay Model

-      A sample of our published results:

- D0 very recent

## W Boson Mass

- W Mass measurements from
- MT(W) @ CDF+D0
- PT(lepton) @ D0
- ET() @ D0
- Using
- electron channels @ CDF+D0
- muon channels @ CDF

- CDF (e+) combined (2000)
- D0 Run 1 (e) Result (2000)

- Uncertainty example (CDF electrons)
- Statistical: 65 MeV/c2
- Systematic: 92 MeV/c2
- ET Scale: 75 MeV/c2
- Detector resolution: 25 MeV/c2
- PDF’s: 15 MeV/c2
- PT(W): 15 MeV/c2
- Recoil Model: 37 MeV/c2
- Backgrounds: 5 MeV/c2

- D0 CC electron channel

## Gauge Boson Self-Interactions

- We study gauge boson couplings by
- investigating properties of
- vector boson pair production
- W, WW, WZ, Z
- in various final states

- Self-interactions are a direct consequence of the non-Abelian SU(2)L x U(1)Y gauge symmetry.
- Trilinear Coupling Diagrams are involved in Vector Boson Pair Production.
- SM makes specific predictions for the strength of the couplings.
- WW and WWZ Couplings related to the static W properties

## WW and WWZ Couplings

- In Run 1:
- Established the EW coupling of  W to  and W to Z.
- The W and WW processes were observed. Candidate WZ events observed.
- Anomalous Coupling Limits     W, WW, and combined WZ results from D0 (equal +Z couplings):
- Another set of relations among couplings

- In 2 fb-1:
- 2000 e+ events per  exp.
- Observe “radiation zero”
- Sensitivity to anomalous couplings ~2-3X better.

- e+ 

## ZZ, Z, and ZZZ Couplings

- Z+photon final state
- Tests ZZand Z couplings
- ZZand Z = 0 in SM    (no s-channel diagrams)

-  14 pb-1 & ee + pb-1

- PRD  4/1/98

- At 95% CL

- Run 1 Limits on coupling parameters

- In 2 fb-1 we expect
- ~600 Z events per experiment
- sensitivity to limits about 5X smaller
- Our first ZZZ limits (CDF observed ZZ candidate with 4 muons in 1995)

- (Z coupling limits similar)

## Top Physics

**Top Physics**

- Pair production mechanisms provide cross section which depends on top mass.
- Top heavier than m(b)+m(W) decays primarily to Wb.

- Topics
- General Features
- Top Pair Production Cross Section & Production Dynamics
- Top Quark Mass
- Branching Ratios & Rare Decays
- Electroweak Top Quark Production

- The Tevatron is the only
- place where we can produce top.

## Top Physics: General Features

- All hadronic and tau+X have             big backgrounds
- Lepton + jets, Dilepton are our best measured channels

## Run 1 result at 1.8 TeV

Run 2
Tevatron beam energy is increased from 1.8 TeV to 2.0 TeV => increase in (ttbar) of 40%.
Uncertainties on signal and backgrounds scale by N-1/2 . Uncertainty on luminosity doesn’t  (~5% in Run 1).

- Run 2
- Tevatron beam energy is increased from 1.8 TeV to 2.0 TeV => increase in (ttbar) of 40%.
- Uncertainties on signal and backgrounds scale by N-1/2** **.** **Uncertainty on luminosity doesn’t  (~5% in Run 1).

**Top-AntiTop Production**

- Event Yields In Run 2a (per experiment)
- Expect @D0 (similar @ CDF).

- Run 1 Results

- Run II Prospects

- * unpublished update of 1998 CDF Pub.

**Notes:**
CDF cross section result is from PRL80 2773, 1998

## Properties of the top events (D0+CDF)

**Properties of the top events (D0+CDF)**

**Top Quark Production Dynamics**

- Distributions as expected
- from SM ttbar production

## Top Quark Mass in Run I

- CDF: Lepton + Jets

- D0: Lepton + Jets

## Top Quark Mass Uncertainties

-     Uncertainties in Run I Lepton+jets mass measurement  @ D0 (CDF)
- Total Systematic: 5.5 (4.9) GeV/c2
- Jet energy scale: 4.0 (4.4) GeV/c2
- Monte Carlo Top Modeling:        3.5 (2.3) GeV/c2
- Principally from uncertainty in Initial and final state radiation
- Background model (Vecbos flavors)  2.0  (1.3) GeV/c2
- Methods 1.2 (0)  GeV/c2
- Statistical [~13 GeV/c2  per event]: 5.6 (4.8) GeV/c2

- How that’s improved in Run II (2fb-1)
-             _Conservative Estimates_
- Systematic: 2.5 GeV/c2
- Jet Energy Scale: 2.2 GeV/c2
- Recalibrate jet energy scale with  +jet, Z+jet, Z->b-bbar, W->jj in top events. There is room for improvement here.
- M. C. Signal Model: 1.0  GeV/c2
- Constrain top production w/ data
- Background Model: 0.5 GeV/c2
- Statistical: 1.0-1.3 GeV/c2
- Reduce combinatorics because of double tags
- Total ~ 2.8 GeV/c2

**Notes:**
Monte Carlo Top Modeling:        3.5 (2.3) GeV/c2
Initial and final state radiation     1.9 (1.8) GeV/c2
PDF’s  0 (0.3) GeV/c2
MC stats 0.8 (0) GeV/c2
Cal Noise, MI Model1.3(0) GeV/c2
b-tagging bias  0 (1.4) GeV/c2

## Top Branching Ratios and Rare Decays

- Within the Standard Model:
- Using indirect estimates of |Vtd| and |Vts|, unitarity, assuming 3 gens:           0.99989 < |Vtb|<0.9993 @ 90% CL

- CDF Result (new)
-      uses ratios of tags in lepton+jets and dilepton events. 0:1:double:2 tags and assuming 3 gens.

- Run 2a (2fb-1): Vtb|~2%

- (95% CL)

- CDF FCNC Search             S.M. Pred. O(10-10)

**Notes:**
Without 3 generations 0<R<0.9993 @ 90% (ie unconstrained)

From Chetyrkin et al prd 60, 114015 (1999) 
Denner and Sack NPB 358, 46, (1991) and 
Mignerond Soni prl 66, 3105 (1991)

## Top Quark Decay Vertex

- Top Quark is unique in that it usually decays before it hadronizes, V-A implies
- W+ is l.h. (h=-1) or long. (h=0)
- i.e. charged lepton tends to be emitted in direction opposite to W line-of-flight.

- S.M. f long ~ 0.7

- Kane, Ladinsky, Yuan PRD 1992

**Notes:**
width  t = (t bW)  1.55 GeV
lifetime   4  10-25 s
QCD time scale 1/QCD  few  10-24 s
may provide a way to pu limits on top lifetime

Lepton pT distribution in tbl distinguishes the two helicity states.
hW= 0: hard pT
hW=-1: soft pT

## Measure angle between the off-diagonal basis and the lepton flight direction in  rest frame of the top -, +

Spin correlation  correlation in + vs - space.        (SM:   0.9)

D0 Measured 

- Spin correlation  correlation in + vs - space. **       (SM: ******** ******** 0.9)**
- D0 Measured

**Top Quark Decay Correlation**

- Spin Configurations
- Optimal spin quantization axis
- Determined once the velocity and scattering angle is known
- Only like-spin combinations are produced in this optimized basis
- G. Mahlon and S. Parke,  PLB 411, 173 (1997**)**

- 

- > -0.25 @ 68% CL

- Fermilab-Pub-00/046-E

## Single Top Production

- Direct access to W  tb vertex
- Measure top quark width and |Vtb|
- Measure of CKM element without any assumptions on number  of generations
- (qq  tb)   (t  W+b)  |Vtb|2

- Theoretical predictions: Smith+Willenbrock, Stelzer et al. For M(top) = 175 GeV

**Notes:**
S-channel Smith+Willenbrock PRD 54, 6696 (1996)
t-channel Stelzer, Sullivan+Willenbrock PRD 56, 5919, (1997) and 
                PRD 58, 094021, (1998)

## Single Top Results: Run 1 vs. Run 2

- D0 Run 1 result at 1.8 TeV
- Signature is e(jj events where one jet is b-tagged with a muon. 90 pb-1. Acceptances:
- Bkgds (W+jets, QCD, top) is 15 events. Expected signal < 1
- Observe 17 events.
- @95%CL:

- Accepted for pub. in PRD

- CDF Preliminary
-  < 13.5 pb
- at 95% CL

- Run 2a (2 fb-1)                will provide a 20% measurement of tb giving Vtb| of 14% at both D0 and CDF.

- CDF’s has better Run I b-tagging (SVX):

**Notes:**
S-channel Smith+Willenbrock PRD 54, 6696 (1996)
t-channel Stelzer, Sullivan+Willenbrock PRD 56, 5919, (1997) and 
                PRD 58, 094021, (1998)

## Top Quark Mass and W Boson Mass 

**Top Quark Mass and W Boson Mass*** *

- W boson  mass + top mass  Constrains Higgs mass

- Tevatron Averages
- M(top)=174.3+-5.1 GeV
- M(W)=80.454+-0.063

**Run 1**

## Search for SM Higgs in Run II

- (H+X) at Tevatron (2 TeV)

- Branching Fractions vs.
- M(Higgs)

## Search for SM Higgs in Run II

- For M(Higgs)<135 GeV/c2
- depends most on b-tagging efficiency and background rejection
- a few signal events per fb-1.
- Background is W+jets
- S/B ~ 1/10

**Best Options for finding Higgs depend on M(Higgs)**

- For M(Higgs)>135 GeV/c2
- Backgrounds are more prosaic forms of diboson production and t-tbar.
- longitudinally polarized W and Z provides some handles on angular distributions
- S/B depends on M(Higgs)
- Varies from 3/30 to 1/4

## Search for SM Higgs in Run II

## Top Quark Mass and W Boson Mass 

- W boson  mass + top mass  Constrains Higgs mass

- M(top)=3.0 GeV
- M(W)=40 MeV

**Run 2**

- Uncertainties shown are slightly bigger than  what we think we can do in 2 fb-1.
- At Run I central values of  M(W) & M(top)

## Conclusions

- The D0 and CDF p-pbar collider experiments have a rich set of preliminary and published results including
- Vector Boson Properties
- W mass, W width, Trilinear gauge boson couplings, and W and Z production properties.
- 3.2 million W to and e expected (per experiment) in 2 fb-1.
- M(W) ~ 30 MeV/c2 per experiment in first 2 fb-1.
- Top Quark Properties
- Top Pair Production Cross Section & Production Dynamics, Top Quark Mass, Branching ratios and Rare Decays.
- M(top) ~ 2.8 GeV/c2 per experiment in first 2 fb-1.
- SM Higgs Boson
- Measurements of M(W) and M(top) hint it is light.
- We restrict the allowed range and find it depending on it’s mass.