# Presentation: 833087

## W Mass Measurement at the Tevatron

- Chris HaysDuke University

**TEV4LHC Workshop**
**Fermilab 2004**

- CDF

- DØ

## Past, Present, and Future

- C. Hays, Duke University, TEV4LHC

*Precision of direct measurements:*

**x**

**x**

**x**

**x**

**2004:**** **
**LEP **
**42 MeV**

**Tevatron **
**59 MeV**

**1983: **
**UA1**
**5 GeV**

**1989: **
**UA1**
**2.9 GeV**

**1990: **
**UA2**
**900 MeV**

**1995: **
**CDF**
**180 MeV**

**2000: **
**D****Ø**
**91 MeV**

**x**

**x**

*W mass now known to better than 5 parts in 10,000*

**Looking forward:**
- * Tevatron Run 2 has quadrupled Run 1 CDF, DØ data sets
- * CDF has analyzed first 200 pb-1 of data and determined uncertainties

- CDF: 79 MeV
- DØ: 84 MeV

**x**

**x**

**x**

**2011:**** **
**Tevatron **
**<15 MeV**

**LHC**
**<15 MeV**

**2004: **
**CDF**
**76 MeV**

**2005: **
**CDF/D****Ø**
**<59 MeV**

**2006: **
**CDF/D****Ø**
**<34 MeV**

**2008: **
**CDF/D****Ø**
**<20 MeV**

**2010: **
**ATLAS/CMS**
**<20 MeV**

**x**

**x**

*~1 fb**-1*

*~0.4 fb**-1*

*~0.2 fb**-1*

**(********M****W****=34 MeV)**

*~4 fb**-1*

**x**

*~10 fb**-1*

## W Mass Fit Distributions 

- W Mass Fit Distributions

- Transverse mass
- * mT2 = 2pTET(1-cos())
- * m ~ 2 pT + u||
- * Low sensitivity to pTW
- * Recoil modelling crucial

- Lepton pT
- * m ~ 2 pT
- * Insensitive to recoil
- * pTW modelling crucial

- u

- u||

- (**u**)

**E****T **= -(**p****T** + **u**)

- mT

- pT

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

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

- C. Hays, Duke University, TEV4LHC

## CDF Run 2 Uncertainties 

- CDF Run 2 Uncertainties

- Scale and resolution:
- : ****W **= **_**+**_ 30 MeV
- e:  ****W **= **_**+**_ 70 MeV

- Scale and resolution:
- ,e: ****W **= **_**+**_ 50 MeV

- C. Hays, Duke University, TEV4LHC

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

- Tower removal:
- : ****W **= **_**+**_ 10 MeV
- e:  ****W **= **_**+**_ 20 MeV

- Production and decay model:
- ,e: ****W **= **_**+**_ 30 MeV

- Backgrounds:
- ,e: ****W **= **_**+**_ 20 MeV

- Statistics:
- : ****W **= **_**+**_ 50 MeV
- e:  ****W **= **_**+**_ 45 MeV

- Transverse mass fit

## Production and Decay Model Uncertainties

- C. Hays, Duke University, TEV4LHC

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

- l _+_

**Parton Distribution Functions**

**QED Radiative Corrections**

- Uncertainty determined from
- 	CTEQ eigenvectors + MRST
- W charge asymmetry
- 	will reduce uncertainty

****W ~ 5 MeV with 4 fb-1

- LHC:  No charge asymmetry
- Constrain PDFs with lepton
- 	 distributions from *W* and *Z*

****W ~ 10 MeV achievable

- Single-photon FSR modelled

- 2-photon FSR needs to be added

****W ~ 5 MeV with 4 fb-1

- (also at LHC)

## Production and Decay Model Uncertainties

- C. Hays, Duke University, TEV4LHC

**p****T****W**** Model**

- Uncertainties determined from RESBOS parameters g1, g2, g3
- Parameters constrained by Run 1 Z pT distribution

- pT fit: 	****W **= **_**+**_ 27 MeV
- mT fit:  ****W **= **_**+**_ 13 MeV

**g**2 **= 0.68 **_**+**_** 0.12 GeV****2**
**g**3 **= -0.60 **_**+**_** 0.30**

****W ~ 5 MeV with 4 fb-1 (pT fit: 10 MeV)

- LHC:  Large *Z* statistics

****W ~ 5 MeV achievable (also for pT fit)

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

******W**

- 70 MeV uncertainty from world average of direct measurements

****W ~ 5 MeV with 4 fb-1

- (also at LHC)

## CDF Run 2 Muon Momentum Calibration

*Set momentum scale using J/**** and upsilon decays to muons*

****W**= **_**+**_ 15 MeV

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

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

- <1/pT()> (GeV-1)

- p/p

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

- Uncertainty from difference in scales:

- C. Hays, Duke University, TEV4LHC

*J/***

- Upsilon

****W**= **_**+**_ 20 MeV

- Post-alignment-correction uncertainty:

- Resolution uncertainty (from *Z* decays):

****W**= **_**+**_ 12 MeV

*Z*

****W ~ 5 MeV with 4 fb-1

- (also at LHC)

## CDF Run 2 Electron Calibration

- Tune upstream passive material using
- tail of *E/p* distribution

- Set energy scale using *E/p* peak

****W**= **_**+**_55 MeV

****W**= **_**+**_35 MeV

- Correct for non-linearity

****W**= **_**+**_25 MeV

- C. Hays, Duke University, TEV4LHC

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

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

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

****W ~ 15 MeV with 4 fb-1

- (also at LHC)

- Resolution uncertainty (from *Z* decays):

****W**= **_**+**_ 12 MeV

## CDF Run 2 Recoil Measurement

*Estimate removed*
*recoil energy *
*using towers *
*separated in ***

- Measure hadronic recoil by summing over all calorimeter towers
- *  Remove towers with energy deposited by lepton

- C. Hays, Duke University, TEV4LHC

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

****W**= **_**+**_10 MeV
- e: ****W**= **_**+**_ 20 MeV

- Removed muon towers

**0.1 x 0.25 ******

- 438
- 1243
- 92

- 9 MeV

****W ~ 5 MeV with 4 fb-1

- (also at LHC)

## CDF Run 2 Recoil Model

- * Parametrize hadronic response: R = **u**meas/**u**true
- * Resolution model incorporates terms from
- 	underlying event and jet resolution

- Resolution at low
- pT(Z) dominated by
- underlying event

- Resolution at high
- pT(Z) dominated by
- jet resolution

*Tune parameters using Z     **** events*

*Model underlying event with minimum-bias data (inelastic collisions)*

****W**= **_**+**_42 MeV

**u**true given by pT(Z)
****W**= **_**+**_20 MeV

- 

- 

- 

**u**

- C. Hays, Duke University, TEV4LHC

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

****W ~ 10 MeV with 4 fb-1

- (also at LHC)

## CDF Run 2 Backgrounds

- C. Hays, Duke University, TEV4LHC

*Electrons*

*Muons*

****W**= **_**+**_ 20 MeV

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

*Muons*

****W ~ 5 MeV with 4 fb-1

- (also at LHC)

## Milestones

- C. Hays, Duke University, TEV4LHC

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

- * Improve understanding of
- 	passive material (E/p tail)
- * Improve COT alignment
- * Understand *W/Z* differences
- 	in recoil model
- * *W p**T* constrained with *Z* *p**T*

- * Detailed understanding of
- 	upsilon/*Z* systematics
- * PDF constrained with *W*
- 	charge asymmetry
- * Include 2-photon FSR

## Ratio Method

- Can also measure mass by measuring *Z* transverse mass for each lepton

***Lower Z statistics (not an issue at LHC)***

*Are there additional systematics?*

***Potentially removes energy calibration uncertainty***

- C. Hays, Duke University, TEV4LHC

*W* transverse mass measurement gives ratio of *W* to *Z* masses

*p**T**W** uncertainty could be  larger than m**T** measurement*

**D****Ø Run 1 Experience (82 pb****-1****)**

## Summary

- Now have Run 2 experience (first milestone hit)

*Recoil differences between W's and Z's*

*Electron energy calibration (passive material)*

***Should be soluble (still early)***

*Modelling 2-photon FSR (in progress) *

**Experimental issues (CDF)**

**Theoretical issues**

*Update PDFs (need input from W charge asymmetry measurement)*

- C. Hays, Duke University, TEV4LHC

*Update p**T**W** parameters (need input from Z p**T** measurement)*

- Preliminary Run 2
- results available

**Potential Improvements at the LHC**

*Can large Z statistics get recoil model below 10 MeV uncertainty?*

*Can PDF uncertainty get below 10 MeV?*

- Most systematics shrinking with increasing data