# Presentation: 548086

## Julien Donini

***Julien Donini***
***University of Padova, INFN***

## Introduction: W/Z Physics

| Leptonic decays |
| --- |
| W mass: constraint on Higgs mass |
| W width: useful tests of SM. Direct and indirect measurements. |
| Drell-Yan qq→ll, AFB: high mll sensitive to New Physics, interference Z/γ*. |
| PDF (parton distribution function) constraints
 x-section W→lν, Z→ll
 differential x-section, Z/γ* rapidity
 W asymmetry.
 Pt distribution. |

| Hadronic decays |
| --- |
| Jet Energy Scales (JES) |
| W→jj: constraint JES, Top mass. |
| Z→bb: b-specific JES, resolution studies. Top, Higgs. |

**Results presented in this talk:**
-  **Z → bb** signal (CDF 0.6fb-1)
-  **Z/****γ********* → e****+****e****-**** rapidity** distribution
-    (CDF 1fb-1, DØ 0.4fb-1)
-  **Z P****t** distribution (DØ 1fb-1)
-  **W charge asymmetry** (DØ 0.2fb-1)

## CDF/DØ Experiments

**CDF/D****Ø detectors**
** ****Silicon vertex tracker**
** ****Solenoid **
** ****Calorimeter (E/H)**
** ****Muons**

|  | CDF | DØ |
| --- | --- | --- |
| Tracking | Drift Chamber + Si, < 2 | Fiber + Si
< 3 |
| Calorimetry | Pb/Steel + Scintillator
< 3.6 | Ur +
Liquid Ar
< 4 |
|  Muons | < 1 | < 2 |

**CDF/D****Ø Experiments**

## Z→bb signal and b-JES

**Large Z****0**** →bb signal: x-section, measure b-specific properties.**

**Use Z****0**** →bb resonance as a tool to:**
** ****measure specific data/MC energy scale of b-quark jets:**
-  Reduction of uncertainty in b-JES helps **Top quark mass**** **measurement
** ****improve b-jet energy resolution**
-  **develop and test algorithm to improve b-jet energy resolution:** important for low mass **Higgs** **searches**.

**b-jets**
- different from generic (light) jets
** ****harder fragmentation**
** ****semi-leptonic decays**
- Play crucial role in **Top** and **Higgs** physics.

**Only triggerable W/Z→jj physical process.**
**Z****→ bb signal was observed in Run I/II.**

## Z→bb signal and b-JES

**Z****→bb signal and b-JES**

**b-specific JES** = scale factor between data and MC Z→bb signal.
**Unbinned likelihood** technique, free parameters: Nsignal and b-jet JES factor.

**f(m****jj****,b-JES)**

**BG model**

**MC signal templates** (Pythia)
- Signal shape **f(m****jj****,b-JES)**

**Data-driven BG model**: BG enriched sample, tag rate function.
- BG models not unique: sideband fit criteria, use all BG model for syst. error.

## Z→bb Results (584 pb-1)

**χ****2****/NDF = 104/75**

**Z****→bb Results (584 pb****-1****)**

- N expected signal used as a constraint to **improve the fit precision** on b-JES factor.

**Results**

**Extraction Z→bb signal and b-specific JES measurements: first step !**
**Applicability of b-JES to other analysis (Top, Higgs, etc) under study.**

- Systematics related to BG models are dominant.

## Z/γ* →e+e- Rapidity Distribution

**Study of  kinematic distributions of Z/****γ********* provide stringent test of QCD calculations.**

- Momentum fraction carried by partons related to Z rapidity:

**Differential x-section measured using ****Z/****γ********* ****→**** e****+****e****-**** decay**
-  lepton accurately reconstructed
-  small backgrounds

- Forward regions (|η|>1.5) most difficult to test

## Z/γ* →e+e- Results (1.1 fb-1)

**Z/****γ********* ****→****e****+****e****-**** Results (1.1 fb****-1****)**

**σ****Tot**** = 265.9 ± 1.0 ± 1.1 pb**

**Compare data/theory:** NNLO calculation with NLO CTEQ6.1 PDF most consistent with data.

**Trigger, acceptance efficiency studies** (data, MC).
**BG sources:** dominant is QCD dijet. Estimated from data. Other processes (diboson, tt, etc) estimated with MC.

**Results:**

**Different topologies:** CC: |η|<1.1, PP: 1.2<|η|<2.8, CP

**Main syst. error:** silicon tracking eff.

## Z/γ* →e+e- Results (0.4 fb-1)

**Z/****γ********* ****→****e****+****e****-**** Results (0.4 fb****-1****)**

- NNLO calculation with MRST2004 NNLO **PDF agrees well with data.**

***Submitted to PRD*****: Fermilab-Pub-07-040-E**

- Statistical uncertainty is dominant.

## Z Boson Pt Measurement 

**Precision measurement of Z boson transverse momentum:**
-  test of theory of weak boson production
-  reduce theoretical uncertainty on W mass
- Measure Z Pt in qq → Z/γ* → e+e- process.

**Event topology** CC: |η|<1.1, PP: 1.5<|η|<3.2, CP.
**Main background:** QCD dijet.

## Z Boson Pt Results (~1 fb-1) 

**Z Boson P****t**** Results (~1 fb****-1****) **

**Z P****t**** spectrum smeared from detector resolution effects ******** unfolding.**

- Largest syst. uncertainty related to lepton ID.
**Syst. uncertainties under study**, expected to be greatly **reduced** in near future.

***960 pb******-1***

## W Charge Asymmetry

**W****±**** rapidity measurement provide useful information about PDF of u and d quarks.**

- Different u, d momentum: **W****±**** produced asymmetrically.**
-  charge asymmetry of decaying l,ν
- But **V-A** interaction: **reduces** the observable asymmetry in the **lepton rapidity distributions.**

**W****+**

##      W→μν Charge Asymmetry (230 pb-1)

**     ****W→μ****ν**** Charge Asymmetry (230 pb****-1****)**

***230 pb******-1***

***230 pb******-1***

**Muon charge asymmetry:**

- Result sensitive to u, d quark momentum in 0.005 < x < 0.3 range.
**Complementary to CDF Run II electron asymmetry analysis (PRD 71, 051104)**.
**Measurement can help constraint the PDFs:** reduce error of some PDF parameters.

- Error bars are **dominated by stat. uncertainty**. Comparable to PDF uncertainty.

## Conclusions

**Large W/Z samples** collected at Tevatron allow many different electroweak measurements.
**Syst. can also be improved in some measurements.**
**Measurements not syst. limited.** Stat. uncertainty will be greatly reduced with increasing amount of data available.
-  Test **theory**, reduce errors on **W mass**, constrain **Higgs mass!**

**Z → bb: preliminary CDF II signal and first b-JES measurement.**
- Applicability of b-JES for other analysis is under study.

## BACKUP

## Z Boson Pt Measurement 

- Event selection:
-  two isolated EM clusters, electron ID
-  high transverse momenta
-  70<mee<110 GeV.
-  track matching of e± candidates

- CC: |η|<1.1, PP: 1.5<|η|<3.2, CP
- Electron triggers.
- ~64000 evts selected

- Electron selection efficiencies (lepton ID, trigger): tag and probe method.

- Main background: QCD dijet.
- Construct inv. mass shape from BG enriched sample
-  then fit data
- Other BG (dibosons, etc): negligible.

## Z_BB Trigger

**Z_BB Trigger**