# Presentation: 904880

## First Run II Measurement of the W Boson Mass with CDF

**on behalf of the CDF Collaboration**

**Oliver ****Stelzer-Chilton**
- University of Oxford

- Rencontres de Moriond EW 2007
- La Thuile, Aosta Valley, Italy, March 11 – 18, 2007

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Outline

- Motivation
- W Production at the Tevatron
- Analysis Strategy
- Detector Calibration
- Momentum Scale
- Energy Scale
- Recoil
- Event Simulation
- Results
- Summary/Outlook

*Outline*

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Motivation

*Motivation*

-  Derive W mass from precisely measured electroweak quantities
-  Radiative corrections r dominated by top quark and Higgs loop
-    allows constraint on Higgs mass

- Current top mass
- uncertainty 1.2%
-            (2.1 GeV)
-  contributes 0.016%
-     (13 MeV) to MW

-  Progress on W mass uncertainty now has the biggest impact on
-   Higgs mass constraint
-  With improved precision also sensitive
-    to possible exotic radiative corrections

- Current W mass
- uncertainty 0.036%
-                  (29 MeV)

-  Higgs mass predicted: 85+39-28 GeV

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## W Production at the Tevatron

- inference of neutrino ET
- (restricted to u<15 GeV)
- Use Z and Zee events to derive recoil model

*W Production at the Tevatron*

- precise charged lepton measurement
- is the key (achieved ~0.03%)

- Combine information into transverse mass:

- Quark-antiquark annihilation
- dominates (80%)

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Measurement Strategy

*Measurement Strategy*

- W mass is extracted from transverse mass, transverse momentum
- and transverse missing energy distribution

- Detector Calibration

-  Tracking momentum scale
-  Calorimeter energy scale
-  Recoil

- Fast Simulation

-  NLO event generator
-  Model detector effects

- W Mass templates

- + Backgrounds

- Data

- Binned likelihood fit

- W Mass

- 81 GeV

- 80 GeV

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## CDF Detector

******

******  ****= 1.0**

******  ****= 2.8**

******  ****= 2.0**

**Silicon tracking **
**detectors**
**Central drift **
**chambers (COT)**
**Solenoid Coil**
**EM calorimeter**
**Hadronic **
**calorimeter**
**Muon scintillator **
**counters**
**Muon drift **
**chambers**
**Steel shielding**

*CDF Detector*

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Tracker Alignment

*Tracker Alignment*

-  Internal alignment is performed
-   using a large sample of cosmic rays
-   Fit hits on both sides to one helix
-  Determine final track-level
-   curvature corrections from
-   electron-positron E/p difference in
-   We decays

-  Statistical uncertainty of
-   track-level corrections leads
-   to systematic uncertainty
-           MW= 6 MeV

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Momentum Scale Calibration

*Momentum Scale Calibration*

- Exploit large J/ and Upsilon
- datasets to set tracker scale
- Tune model of energy loss
-  J/ independent of muon pT
- Apply momentum scale to Z’s

- MW= 17 MeV

- good agreement with
- PDG (91187±2 MeV)

- Tune resolution on width of di-muon mass peaks

- Υ→μμ

- Z→μμ

- MW= 3 MeV

**Data**
**Simulation**

**Data**
**Simulation**

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Energy Scale Calibration

- Transfer momentum calibration to calorimeter using E/p
- distribution of electrons from W decay by fitting peak of E/p
- Tune number of radiation lengths
- with E/p radiative tail
- Correct for calibration ET dependence
-                 Tune resolution on E/p and Z mass peak

*Energy Scale Calibration*

- W→eν

- E

- p

**Data**
**Simulation**

**Data**
**Simulation**

- Add Z Mass fit to calibration
- (30% weight)

- good agreement with
- PDG (91187±2 MeV)

- Apply energy scale to Z’s

- MW= 30 MeV

- Z→ee

- MW= 9 MeV

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Hadronic Recoil Definition

*Hadronic Recoil Definition*

-   Recoil definition:
-   Vector sum over all calorimeter
-       towers, excluding:
-       - lepton towers
-       - towers near beamline
-         (“ring of fire”)

- Electrons: Remove 7 towers keystone
- MW= 8 MeV
- Muons: Remove 3 towers (MIP)
- MW= 5 MeV
- Model tower removal in simulation

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Hadronic Recoil Model Calibration

*Hadronic Recoil Model Calibration*

-  Use Z balancing to calibrate
-   recoil energy scale and to
-   model resolution
-  Calibrate scale (R=umeas/utrue)
-   with balance along bisector axis
-   MW= 9 MeV
-  Resolution has two components
-   -soft (underlying event)
-   -hard (jets)
-  Calibrate along both axes,  & 
-   MW= 7 MeV

- 

- 

- 

**u**

**Data**
**Simulation**

**Data**
**Simulation**

- 

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Recoil Model Checks

*Recoil Model Checks*

-  Apply model to W sample to
-   check recoil model from Z’s
-  Recoil projection along lepton u||
-    directly affects mT fits
-    Sensitive to lepton removal,
-       scale, resolution, W decay

-  Recoil distribution
-    sensitive to recoil scale
-       resolution and boson pT
-  Recoil model validation plots
-   confirm consistency of the model

**Data**
**Simulation**

**Data**
**Simulation**

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Boson pT Model

*Boson p**T** Model*

-  Model boson pT using RESBOS
-   generator [Balazs *et.al.*
-   PRD56, 5558 (1997)]
-  Non-pertubative regime at low
-   pT parametrized with g1, g2, g3
-   parameters

-  g2 parameter determines
-   position of peak in pT distribution
-  Measure g2 with Z boson data
-   (other parameters negligible)
-  Find: g2 = 0.685±0.048
-   MW= 3 MeV

**Data**
**Simulation**

**Data**
**Simulation**

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Production, Decay and Backgrounds

*Production, Decay and Backgrounds*

-  QED radiative corrections:
-   - use complete NLO calculation (WGRAD)
-     [Baur *et.al.* PRD59, 013002 (1998)]
-   - simulate FSR, apply (105)% correction for 2nd 
-      MW= 11 (12) MeV for e ()
-  Parton Distribution Functions:
-   - affect kinematics through acceptance cuts
-   - use CTEQ6 ensemble of 20 uncertainty PDFs
-     MW= 11 MeV
-  Backgrounds:
-   - have very different lineshapes
-     compared to W signal
-   - distributions are added to template
-   - QCD measured with data
-   - EWK predicted with Monte Carlo
-     MW= 8 (9) MeV for e ()

|  |  |  | Background |  |  |  | %(Muons) |  |  | %(Electrons) |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  | Hadronic Jets |  |  |  |  |  |  | 0.10.1 |  |  |  | 0.250.15 |  |
| Decay in Flight |  |  |  |  |  |  |  |  | 0.30.2 |  |  |  | - |
|  |  | Cosmic Rays |  |  |  | 0.050.05 |  |  |  |  |  |  | - |
|  |  |  |  |  | Zll |  |  |  | 6.60.3 |  | 0.240.04 |  |  |
|  |  |  |  | W |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  | 0.890.02 |  |  |  |  | 0.930.03 |  |  |

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## W Mass Fits

*W Mass Fits*

- mW = 80417 ± 48 MeV (stat + syst)
-     combination yields P(2) = 7%

- Transverse mass fits:

- Muons

- Electrons

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## W Mass Fits

*W Mass Fits*

- Also fit ET and ET distributions in muon and electron channel and combine with transverse mass fits:

- Electron ET fit

-      mW = 80413 ± 48 MeV (stat + syst)
- combination of all six fits yields P(2) = 44%

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Systematic Uncertainty

-                    Systematic uncertainty on transverse mass fit
-                      ⇒ Combined Uncertainty: 48 MeV for 200 pb-1

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Results

-  New CDF result is the world’s most
-   precise single measurement
-  World average increases:
-   80392 to 80398 MeV
-  Uncertainty reduced ~15%
-   (29 to 25 MeV)

-  Standard Model Higgs (LEPEWWG)
-   constraint: 80+36-26 GeV
-   (previous: 85+39-28 GeV)

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Summary/Outlook

*Summary/Outlook*

-  First Run II W mass measurement completed using 200 pb-1 of data
-  With a total uncertainty of 48 MeV
-    worlds most precise single measurement

-  Projection from previous Tevatron measurements
-  Expect MW < 25 MeV with 1.5 fb-1 already collected

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Backup

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Standard Model Higgs Constraint

-  Previous SM Higgs fit:
-   - MH = 85+39-28 GeV
-   - MH < 166 GeV (95% CL)
-   - MH < 199 GeV (95% CL) Including LEPII direct exclusion
-  Updated preliminary SM Higgs fit:
-   - MH = 80+36-26 GeV (M. Grünewald, private communication)
-   - MH < 153 GeV (95% CL)
-   - MH < 189 GeV (95% CL) Including LEPII direct exclusion

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Systematic Uncertainty

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Signed 

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## W Mass Measurement

*p**T**W **= 0*
*p**T**W **≠ 0*
*measured*

*m**T*
-  Insensitive to pTW to 1st order
-  Reconstruction of pTν sensitive
-    to hadronic response and
-    multiple interactions

*p**T** *
-  Less sensitive to hadronic
-    response modeling
-  Sensitive to W production
-    dynamics

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Full Electron Simulation

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Consistency of Radiative Material Model

*Consistency of Radiative Material Model*

-  Excellent description of E/p tail
-  Radiative material tune factor:
-   Smat=1.0040.009stat0.0002bkg
-  Z mass reconstructed from
-   electron track momenta

- geometry confirmed:
-     Smat independent of ||

- Measured value in good
- agreement with PDG

**Data**
**Simulation**

**Data**
**Simulation**

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Lepton Removal

- Electrons: Remove 7 towers
-                 keystone (shower)
-              MW= 8 MeV

-  Estimate removed recoil energy using towers separated in Φ
-  Model tower removal in simulation

- Muons: Remove 3 towers (MIP)
- MW= 5 MeV

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Hadronic Recoil Response Calibration

*Hadronic Recoil Response Calibration*

-  Project vector sum of pT(ll) and u on orthogonal
-   axes defined by lepton directions
-  Use Z balancing to calibrate recoil energy scale
-  Mean and RMS of projections as a function of
-   pT(ll) provide information for model parameters

- Hadronic model parameters
- tuned by minimizing 2
- between data and simulation

- MW= 9 MeV

**Data**
**Simulation**

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Progress since 1995

- 2007 indirect mt and mw

- 2007 direct mt and mw

- 1995 direct mt and mw

- 1995 indirect mt and mw

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Momentum Scale Calibration

- Central Outer Tracker: Open-cell drift chamber

-  Use clean sample of cosmic
-    rays for cell-by-cell internal
-    alignment
-  Fit COT hits on both sides
-    simultaneously to a single
-    helix
-  Measure cell tilts and shifts

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007

## Alignment Example

- Cell shift (microns)

- Final relative alignment of cells ~5m (initial alignment ~50m)

- Oliver Stelzer-Chilton - Oxford

- Moriond EW 2007