# Presentation: 659777

## Review of W and Z      physics at the Tevatron 

- Review of W and Z      physics at the Tevatron

- Sandra Leone
- (INFN Pisa)
- for the CDF and DØ Collaborations
- HEP EPS Lisbon, July 21-27 2005

## Outline

- The Tevatron & the experiments
- Motivations for EWK physics at the Tevatron
- W and Z Cross section measurements (e,,)
- W and Z asymmetries
- W Mass and Width
- Summary and prospects

## Why W/Z  Measurements at the Tevatron? 

- Why W/Z  Measurements at the Tevatron?

- Precise  Electroweak measurement  one of the main physics goals at Tevatron
- They can either:
- Constrain the Standard Model
- OR
- Provide evidence of Physics Beyond SM
- Also crucial as input for LHC physics program:
- Input to Parton Distribution Functions
- Some Tevatron signals will be LHC background
- After LEP era we are now into Tevatron era:
- Tevatron is for the next few years the only accelerator that can produce Ws and Zs directly

## The Tevatron Collider

-  Run II: s = 1.96 TeV
-  Started in spring 2001
-  After a commissioning period, data  “good for physics’’ since February 2002

**1.2 x 10****32**

- Peak Luminosities above   1 x 1032 cm-2 s-1 now common
_**Record:**_ initial lum ~ _1.35 x 10__32_ cm-2 s-1 on _May 2005_
- Integrated luminosity per week ****** **15 pb-1

- Peak luminosity

## CDF & DØ 

-  12 countries     62 institutions ~700 authors

-  19 countries      86 institutions ~620 authors

- CDF & DØ

## Integrated Luminosity

- Start of physics-quality data

- on tape  ~800 pb-1

-  delivered: 1fb-1 milestone reached May 23, 2005!

- Detectors running stably since Feb. ’02
- Data taking  efficiency L(recorded/L(delivered)              commonly  > 85%

- All results shown in the following based on datasets ranging from   ~70 to 400 pb-1

## W/Z Production Processes 

- W/Z Production Processes

- Tevatron is a vector boson factory: *)
-  ~90,000 W-> e**** events/week
-  ~8000 Z-> ee/ events/week
-  ~200 WW, 60 WZ events/week
- 			*) for L ~ 15 pb-1/week

## W/Z Gauge Bosons Identification 

- W/Z Gauge Bosons Identification

- At hadronic collider W and Z bosons hadronic decays are overwhelmed by QCD background.
-  Identification through leptonic decays

- We

- Z

- W**±** signature:  Isolated Energetic  Lepton + ET

- Z Signature: Two Isolated Energetic  Leptons (opposite charge)

- ET>25GeV

- PT>20GeV

- PT>20GeV

## Z0  Boson Production 

- Z0  Boson Production

- cand
- 177 pb-1

- cand
- 148 pb-1

- Zee

- Z****

- CDF:PRL 94, 091803 (2005)

- 72 pb-1
- cand

- 72 pb-1
- cand

## W±  boson production

- W±  boson production

- CDF: PRL 94, 091803 (2005)

- 116569 cand
- 177 pb-1

- 62285 cand
- 96 pb-1

- W****

- We****

- 31722 cand
- 72 pb-1

- 37584 cand
- 72 pb-1

- 10461 c.
- 64 pb-1

- 1.1<****<2.8

## Electroweak physics with 

- Electroweak physics with ****

- _D__Ø__ __ _separates taus into 3 categories based on final state particles,      **** identified with  Neural Network

- _CDF_ uses cut based tau identification
- defines signal and isolation cone around seed track direction
-  0 information is added
- Require track & 0 isolated

- Type 1: 1 track

- Type 2: 1 track with EM en. Type 3: more than 1 track

- Z    is irreducible background to Higgs   search

## Z  h

- Use channel ****1   **** + ****2  had or e  isolated muon (pT > 12 GeV) opposite tau object
- split sample into opposite sign (OS) ******** and same sign (SS) ********
- Use SS data to predict QCD bkgnd
- W+j shape from MC and normalization from data
- Compare output of NN for  OS data and background for all tau types

- PRD 71, 072004 (2005)

- L = 226 pb-1

- xBr(Z) = 237 ± 15(stat) ± 18(sys) ± 15(lum) pb

## Z  eh

- Use channel ****1   e + ****2  had : isolated electron (ET>10 GeV/c) and hadronic tau (pT>15 GeV/c)
- Event topology cuts to reject qcd and W+jet backgrounds
- Cross section consistent with SM expectation

- L = 350 pb-1

##  Inclusive W/Z Cross Sections

-  Inclusive W/Z Cross Sections

******Th,NNLO**=251.3±5.0pb

******Th,NNLO**=2687±54pb

- • Overall good  agreement with the NNLO calculations                                  • Accuracy limited by the systematic effects                                                • Uncertainties dominated by the luminosity measurements (~6%)                  • Other systematics: dominated by PDF uncertainties (~2%) in e/,     tau algo in **** channels

## Lepton Universality in W Decays

- From the measurements of the W  e and W  μ  cross sections
- obtain cross section ratio U:

- Many systematic uncertainties
- cancel out

- .Br(W->ev)

- =

- Γ(W->μv)

- Γ(W->ev)

- =

- In the same way from W  e and  W   cross sections:

## Indirect W Width Measurements

- Checking internal consistency in the EWK sector of SM comparing with * *direct Γ(W) measurement
**   **convert measured value of
- into  a measurement of the W width:

- Many systematic uncertainties cancel out (e.g. luminosity)

- PRL 94, 091803 (2005)

## Z forward-backward Asymmetry

- A**FB** arises from Axial and Vector couplings Z and  interference term:

-  Complementary to LEP, far from the Z pole
-  Sensitivity to heavy neutral bosons (Z')
-  At high Mee limited by statistics

- p

## Z  AFB

- Z  AFB

- Distributions consistent with SM predictions

- L= 177 pb-1

- L= 72 pb-1

- CDF extracted quarks and electron couplings:
- and sin**2********W****Eff****=0.2238**±**0.004**±**0.003**

- PRD 71, 052002 (2005)

##  d/dM (Z/*  e+ e-)

- Invariant mass distribution is computed correcting data for effects due to:
- Detector resolution
-  Acceptance
- QED Radiative corrections
-  Background 1% (fake e's)
-  Main sys. uncertainties:
-  background estimate
-  PDF
-  detector modeling
-  Z pT in MC

- NNLO theory prediction from
- Nucl. Phys. B **359**, 343 (1991)

- L= 177 pb-1

##  d/dy(Z/*  e+ e-)

- L= 337 pb-1

- The use of the DØ  forward calorimeter provides data over almost the entire rapidity range accessible at Tevatron. Generally good agreement with NNLO prediction                71 < Mee < 111 GeV/c2

- The momentum fraction of parton from proton is related to y of the   Z boson:
-  in principle this measurement can provide information to constrain the parton distribution functions (PDF) at high Q2 (~ Mz2) in the high x region (x>0.3)

**Notes:**
This measurement (dsigma/dy) can provide information to constrain the parton distribution functions at Q2 = MZ2

## W Charge Asymmetry

**←****anti-proton direction   proton direction→**

-  u quark inside proton carries higher fraction of p momentum than d-bar quark
-  Use W’s to probe the proton structure:
- obtain info on momentum distributions of the quarks and gluons (PDF's)

##  W Charge Asymmetry 

- Production  asymmetry in ppbar->WX is sensitive to U/D
- _Measured: e asymmetry:_
-  convolution of W production
-  asymmetry + V-A decay
- charge ID at high || is crucial
- misID probability ~4% at |η| ~ 2
-  Bin data in ET (2 bins) to increase                                                                sensitivity

**∫**Ldt=170pb-1

- PRD71, 051101(2005)

## Introduction to W Mass

- ΔMW= 34 MeV

-  Precise knowledge of MW (and Mtop) constrains SM Higgs mass
-  MW known to a precision of 34 MeV:
- LEP: 	     80,447 42 MeV
- Tevatron:  80,454 59 MeV (Run I)
- Uncertainty: 79 MeV (CDF), 84 MeV (DØ)

- W mass fundamental parameter of SM
-  Radiative corrections: depend on Mtop and MHiggs
-  W propagator includes H, tb, hypothetical new particle loops

- Run II Goal: uncertainty < 40 MeV per experiment

## W mass measurement strategy

- W mass obtained from fit of transverse mass **M****T****(l********)**
- use Z events to model detector response to hadronic recoil energy and calibrate the charged lepton resolution
- obtain charged lepton scale using
- J/+ Upsilon mass for momentum scale
- E/p in W events for energy scale                                         (greater  stat. precision than Z)
- use Z events to cross check
- W production model:
- Use Z decay to  model boson pT distr.
- QED corrections to W/Z decay
- QCD corrections to W/Z production
- Will use next PDFs fits with CDF W                                       charge asymmetry measurement                                          included

**CDF RUN II**
**PRELIMINARY**

**CDF RUN II**
**PRELIMINARY**

## CDF RunII W Mass

**CDF RUN II**
**PRELIMINARY**

- Total uncertainty: 76 MeV/c2 (e+**** combined) already
- lower  than CDF Run 1 (79 MeV/c2)

- muons

- electrons

- Fits still blinded

- With L=200pb-1  of Run II data CDF estimated the uncertainty on MW

- MT

- MT

##  W width: direct measurement 

-  W width: direct measurement

- Determine W width using the tail of MT(e****) distribution
- Normalization: 50<MT<100 GeV/c2
- 625 events 100 < MT < 200 GeV/c2 signal region
-  consistent with SM and indirect measurements
-  Syst. error dominated by EM&Had resolution and underlying event
-  Total uncertainty already lower than DØ run 1

**signal region: 100-200 GeV/c****2**

**normalization**

****W= 2.011  0.142 GeV

- Standard Model

- L= 177 pb-1

- MT

## Summary & Prospects 

- Most of Run I Tevatron EWK measurements already improved in Run II:
- EWK measurements with lepton channels (e; ****; **** ) achieve a few % precision.
- Z **** established: a milestone in ppbar coll. Physics
- New W charge asymmetry data included in PDF’05 fits
- First Run II direct measurement of the W width
- All results are consistent with SM
- Looking forward to high precision measurements:
- W mass and width could reach ΔMW~30 MeV, ΔΓW~50 MeV with 2 fb-1
- Tevatron experiments just starting to explore potential of Run II data: stay tuned!