# Presentation: 574078

## Electroweak Physics Prospects in Run 2 with the DØ Detector at the Tevatron Collider

**Alan L. Stone**
**    ****Louisiana Tech University**
***...******on behalf of the DØ Collaboration***

** ****Tevatron Upgrade**
** ****D****Ø Detector Upgrade**
** ****Run 2 EW Physics Prospects**
** ****Preliminary Analysis **
** ****Summary & Goals**

## Run 2 Tevatron Upgrade

**Main Injector**
** ****& Recycler**

**Tevatron**

**Chicago**
****

******p source**

**Booster**

******p **

**p **

**p **

******p **

**1.96 TeV **

**CDF**

** ****D****Ø**

** ****Higher Energy     **
**   ****1.8 TeV ******** 1.96 TeV**
** ****Increased Luminosity**** **
**    ****0.1 fb****-1**** ******** 2 fb****-1 ******** 15 fb****-1**

## The Run 2 DØ Detector

**Builds on the firm foundation of the Run 1 calorimeter and central muon system**
**Adds magnetic tracking, silicon, new forward muon system, new electronics and three level trigger **
**Electroweak analyses make use of the full detector capabilities**

**The Run 2 DØ Detector**

## Run 2 Detector Performance

**Muon System**
**reduced backgrounds and trigger rates with additional shielding**
**lower thresholds (no prescale): single muon *****p******T***** ****> 7 GeV, dimuon *****p******T***** ****> 2 GeV**
**Calorimeter**
**performance at 5x10****32 ****cm****-2**** s****-1**** comparable to Run I performance at 2x10****31**** cm****-2**** s****-1**
**ability to *****in situ***** calibrate (*****E***** vs *****p***** now available)**
**Preshowers**
**electron ID (central and forward)**
**forward electron triggering: additional x3-5 rejection over calorimeter alone****	**
**Triggering**
**increased bandwidth: 7 MHz L1, 10 kHz L2, 1 kHz L3, 50 Hz to tape**
**more than an order of magnitude improvement over Run 1 system **

** ****Important additions to DØ physics capabilities: **
**   ****E/p matching for electron ****	****identification**
**    ****Improved muon ****	****momentum resolution**
**    ****Charge sign & momentum ****	****determination**
**     ****Calorimeter calibration**
**     ****Displaced vertex ****	****identification**

## Data Recorded by the DØ Detector

**Detector commissioning,**
**timing, improve electronics, **
**DAQ and offline**

**Fully**
**Instrumented**
**Fiber Tracker**

**First Collisions**

**Run 2 **
**start**

**Detector Roll-in**

******40 pb****-1**** delivered by May 2002 **
** ****About 25 pb****-1**** used for detector **
**  ****commissioning**
** ****Timing, triggering**
** ****Data Acquisition System**
** ****Tracking, Alignment**
** ****object ID: e, ********, ********, ********, W, Z**
** ****E/p, E****T****, jets, etc.**
** ****Starting to do physics...**

## General Features of W & Z Production

**Distinctive lepton decay event signatures**
** ****High P****T**** isolated leptons (e or ********)**
** ****One high P****T**** lepton + Missing  E****T ****(W)**
** ****Two high P****T ****leptons (Z)**

**Cross Sections**
**increase by 20% from **
**1.8-2.0 TeV**

**W********l********  ******** ~1 Hz @ L = 2********10****32**

**Run 2**
**Expected**
**Rates**

## Run 2a EW Physics Prospects for DØ

**W & Z cross sections in electrons and muons**
**W boson mass and width**
**W charge asymmetry  **
**Trilinear gauge boson couplings**
**W ******** analysis and radiation zero**
**Z’ search**

## W & Z Cross Sections

**Previous Tevatron results**

-  **Measurement errors:**  Stat  Sys ~ 2%,   Luminosity error ~ 4%
-  **Theory error:**  ~ 3%, NNLO, O(s2) (Hamberg, van Neerven, Matsuura)
- Dominated by PDF’s at NLO

## Measurement of the W Width

**Indirect Method**

**Direct Method**

**Perturbative**
**QCD**

**LEP**

**W Width**

**Measure**

**SM **
**EW**

** ****Total width of *****W***** boson can be**
**   ****measured directly from the tail **
**   ****of the transverse mass distribution.**
** ****Less model dependent than indirect**
**  ****method – dominated by Breit-Wigner, **
**  ****not detector effects.**
** ****The lineshape measurement would**
**   ****yield better results with luminosity**
**   ****greater than 15 fb****-1****. **

**Deviations from the SM**
**prediction would signal **
**the presence of new decay modes of the W boson.**

## W Boson Mass Preliminaries

**W Boson **
**Production **
**& Decay **
**Model**

**D****Ø 1994-1996**

** ****Theoretical calculations tuned by our measurements.**

** ****Uncertainties in vector boson production at small p****T**** are a major source of uncertainty in mass of *****W***** boson **
** ****Z: Similar production characteristics & decay e****+****e****-**** very well measured – constrain Z/W prod. models**
** ****Probe non-perturbative, resummation  & fixed-order QCD effects (all values of p****T****)**
** ****Good agreement w/ Ladinsky-Yuan parameterization **

**P****T****(Z) spectrum**

** ****Probe effects of NLO QCD corrections on the spin structure of W boson production**
** ****Transverse mass of W boson is correlated with the decay angle of the lepton**

**Electron angular **
**distribution parameter**

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

## W Boson Mass  

** ****Precision measurement of **
***W***** mass of ~30 MeV/c****2****  with 2 fb****-1**** of Run 2a data should be possible**

***W***

***W***

***b***

***W***

***W***

***W***

*******m******W **********m******t*****2**

*******m******W *********ln *****m******H***

***t***

***H******0***

**DØ**
**Run 2a**
**Prediction**

** ****EW symmetry breaking gives mass to the *****W***** boson **
** ****Aside from radiative corrections ********r****EW****, *****W***** boson mass is determined by three precisely measured quantities:  *****M*****Z****, *****G*****F**** and ******

** ****Derive the size of  ********r****EW**** from the measured *****W***** boson mass**
** ****Dominated by loops involving the top quark & Higgs boson**

** ****With a precision of  20 MeV/c****2****  for the *****W***** mass and  **
**2 MeV/c****2**** for the top quark mass (Run 2b, 15 fb****-1**** ), the Higgs Boson mass can be further constrained. **

## W Charge Asymmetry

***u***** quarks tend to carry more momentum than *****d***** quarks, so the *****W******+***** (*****W******-*****) is boosted in the proton (antiproton) direction**
**A precision *****W***** charge asymmetry measurement will discriminate between PDFs**
**Reduce uncertainty from PDFs in the *****W***** mass measurement**

***A******w******(y) *****is closely related to the slope of the *****d(x)/u(x)***** quark distribution at high *****Q******2***** (*********M******w******2*****)**

**Efficiencies &**
**acceptances**
**cancel out**

***W***** charge asymmetry is inferred from the lepton rapidity asymmetry.**

***W***** Charge Asymmetry**

## Gauge Boson Self-Interactions

**Trilinear coupling diagrams are involved in vector boson pair production.**
**SM makes specific predictions for the strength of the couplings.**
***WW*********** & *****WWZ***** anomalous couplings are related to the EM multipole moments of the *****W***

**We investigate properties of vector boson pair production *****W*****************, *****W******+******W******-*****, *****W************Z***** in various final states in order to test the nonabelian couplings of photons, Z’s and W’s**

**q****e****W**** = -e(******** -********) / M****2****W**

******W ****= e(1+******** + ********)/2M****W**

***...******where ************ = (************-1) = ************= 0 in SM ***

**‘****Anomalous’ couplings represent possible**
**deviations from the SM predictions.**

**Leading order tree level Feynman diagrams **

**qq******

**Radiative decay**

**ISR**

**WW******

**From MC cross section calculations: with non-SM couplings, the trilinear diagram contribution becomes larger with larger anomalous couplings**
**By counting *****W*********** events & measuring the cross section, the coupling effect can be measured**

## Anomalous Coupling Limits

***Run 1:*****  Anomalous coupling limits from combined DØ results of *****W***********, *****WW***** and *****WZ***** cross section measurements (equal ******** +Z couplings)**

** ****Expect ~2000 ****W******** events in Run 2a**
** ****Improve by 2-3x over Run 1 limits**

**Run 1**

**Run 1**

***Run 2 Predictions***

## W  Candidate

**Track match**
**to an electron**

**ME****T**** = 24.8 GeV**

**           ******

**Photon, p****T**** = 58 GeV/c**

**Electron, p****T**** = 20 GeV/c**

**Run 2 **
**Preliminary**

**Run 2 **
**Preliminary**

## Radiation Amplitude Zero

**Monte**
** ****Carlo**

** ****...************* is the scattering angle of the photon relative to the quark direction in the *****W***********  CM rest frame **

**Monte**
** ****Carlo**

** ****Effect of the anomalous couplings is to fill in the zero.**
** ****Never before observed.**

**SM**

**SM**

******=1.5**
******=0**

******=0**
******=1.5**

******=1.5**
******=0**

******=0**
******=1.5**

** ****Due to the interference of the different SM diagrams, the *****W*********** differential cross section vanishes at a particular point in phase space, called the *****‘radiation zero’ ***

** ****Extra coupling between the *****W***** & ********** leads to excess of events, visible at high ****E****T****.**

**Cos ************* = -1/3(+1/3) for W****+****(W****-****)**

## W e  Event Sample

**M****T ****(GeV/c****2****)**

**M****T ****(GeV/c****2****)**

***Events***

***Events***

***W************ e***********  Event Sample**

**Background**
**subtracted**

***Major source of background:***
- dijet events where one jet passes EM id cuts & the MET is mismeasured.
- Also: W, ee & ttbar.

**No Track**
**Matching**

**With Track**
**Matching**

**Run 2 **
**Preliminary**

**Run 2 **
**Preliminary**

***Missing  ***
***Transverse ***
***Energy***

**Run 2 **
**Preliminary**

***Transverse***
***Mass***

**Run 2 **
**Preliminary**

**Run 2 **
**Preliminary**

***W Transverse***
***Momentum***

## W   Event Candidate

**E****T**

**Central track matched to muon**
** ****Transverse Mass = 78 GeV **
** ****11 Hits & DCA ****= 50********m**

**Pbar**

**P**

**R-Phi**
**plane**

******

******

**Muon p****T**** = 37 GeV**
**Charge = -1**
**2.6 GeV (MIP) in Calorimeter**

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

## Z  e+e-

***Z ************ e******+******e******-***

** ****in Z peak (75-105 GeV)**
** ****outside Z peak**** **

**E/p**

**Events**

**No Track**
**Matching**

**With Track**
**Matching**

**Preliminary Run 2 data **
**(~3 pb****-1**** from Jan-Mar 2002)**

**Matched track:**
** ****| ********electron****- ********track****| < 0.02 **
** ****Close to vertex (< 1 mm)**
** ****|E/P|<2 **

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

## Di-Muon Mass Plots

**Central track matched with muon**

**p****T**** > 15 GeV**

**p****T**** > 2 GeV**

****

**J/******

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

**Run 2**
**Preliminary**

## Z  +-  Event Candidate

**Two muons with matched**
**central tracks**

**Invariant mass = 102.7 GeV**

**R-Phi**
**plane**

******         **

**          ******

**Run 2**
**Preliminary**

## DØ Summary & Goals

**Improved DØ detector for Run 2**
**2T solenoid, superior tracking, forward muon, faster electronics, three level trigger system**
**We are reconstructing electrons, muons, jets, missing E****T****, ****J/********, W’s and Z’s**
**Working hard to understand our backgrounds**
**From Run 2a integrated luminosity of 2 fb****-1**
**A few million *****W***** & hundreds of thousands of *****Z *****events**
**Precision measurements of *****W***** mass & width**
**Cross sections at higher energy**
**Improve anomalous coupling limits & charge asymmetry measurements**
**QCD:  *****W***** & *****Z***** transverse momentum measurements**
**Radiation zero**
**We are on the way to exciting physics!**