Measurement of W boson mass at D Junjie Zhu State University of New - - PowerPoint PPT Presentation

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Measurement of W boson mass at D Junjie Zhu State University of New - - PowerPoint PPT Presentation

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Measurement of W boson mass at D Junjie Zhu State University of New York at Stony Brook y y Fermilab Users Meeting Fermilab Users Meeting June 3 rd , 2009 Thank you! An award for the whole D collaboration High precision

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SLIDE 1

Measurement of W boson mass at DØ

Junjie Zhu State University of New York at Stony Brook y y Fermilab Users Meeting Fermilab Users Meeting June 3rd, 2009

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SLIDE 2

Thank you!

An award for the whole DØ collaboration High precision measurement needs excellent understanding of High precision measurement, needs excellent understanding of

the DØ detector

Thought it was hopeless to do the DØ W mass measurement in

g p Run II before 2005

It took many people many years’ hard work to make this

measurement possible

Special thanks to: Th W

ki

The W mass working group The electroweak physics group The calorimeter operation and calibration gro ps The calorimeter operation and calibration groups Mentors and others that I have worked with University of Maryland (Sarah Eno Nick Hadley Marco University of Maryland (Sarah Eno, Nick Hadley, Marco

Verzocchi) and Stony Brook (Paul Grannis, John Hobbs, Bob McCarthy)

2009-06-03 Junjie Zhu 2

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SLIDE 3

W boson mass

1 1

2

MW = πα ) 1 ( sin 2

2

r G M

W F W

Δ − θ

Δ M 2 Δr ∝ logM Δr ∝ Mt

2

Δr ∝ logMH

2009-06-03 3 Junjie Zhu

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SLIDE 4

W boson mass

1 1

2

MW = πα ) 1 ( sin 2

2

r G M

W F W

Δ − θ

Δ M 2 Δr ∝ logM Δr ∝ Mt

2

Δr ∝ logMH M b i d b t 250 M V i MSSM

2009-06-03 4

MW can be increased by up to 250 MeV in MSSM

Junjie Zhu

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SLIDE 5

Higgs mass constraints

2009-06-03 5 Junjie Zhu

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SLIDE 6

Higgs mass constraints (1998)

2009-06-03 6 Junjie Zhu

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SLIDE 7

Higgs mass constraints (2002)

2009-06-03 7 Junjie Zhu

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SLIDE 8

Higgs mass constraints (2006)

2009-06-03 8 Junjie Zhu

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SLIDE 9

Higgs mass constraints (2009)

New DØ result is not included

2009-06-03 9 Junjie Zhu

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SLIDE 10

MW and Mtop uncertainties

10 2009-06-03 Junjie Zhu

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SLIDE 11

MW and Mtop uncertainties

11

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MW and Mtop uncertainties

Need ΔMW ≈ 0.006 ΔMtop in order to make equal contribution to the SM Higgs mass uncertainty ΔM (WA) 1 3 G V ΔM 8 M V ΔMtop(WA) = 1.3 GeV → ΔMW = 8 MeV ΔMW(WA) = 25 MeV → ΔMW is the limiting factor

12

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SLIDE 13

Measurement strategy

W→eν Z→ee

) (υ pT r

Three observables: pT(e), pT(ν) (inferred from missing transverse

energy), transverse mass l i d i l i i h

MT

2=(ETe+ETν)2-|pTe+pTν|2

Develop a parameterized MC simulation with parameters

determined from the collider data (mainly Z→ee events)

Generate MC templates with different input W mass values Generate MC templates with different input W mass values,

compare with data distributions and extract MW

Z →ee events are used to set the absolute electron energy scale, so

  • gy

, we are effectively measuring MW/MZ

2009-06-03 13 Junjie Zhu

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SLIDE 14

W→eν candidate

El t Electron Electron Recoil MET R il MET Recoil

Crucial to understand the calorimeter response to the electron

(~40 GeV) and the recoil system (~ 5 GeV) ( 40 GeV) and the recoil system ( 5 GeV)

To measure MW with an uncertainty of 50 MeV: Need to understand the electron energy scale to 0.05%

  • gy

Need to understand the recoil system response to <1%

2009-06-03 14 Junjie Zhu

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SLIDE 15

DØ detector

CC EC

2009-06-03 Junjie Zhu 15

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SLIDE 16

Uranium-LAr calorimeters

CH CH FH FH CH EM

Four EM layers

EM FH CH

~ 46 000 readout channels

Recoil system is measured using the whole calorimeter system 2009-06-03 Junjie Zhu 16

~ 46,000 readout channels

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SLIDE 17

Material in front of the calorimeter

CPS: 0.3 X0 + 1 X0 of lead

Cryostat walls: 1.1 X0 EM1

~ 3.6 X0 for η=0

0.9 X0

inner detector: 0 3 X

Interaction point

~ 5.0 X0 for η =1 inner detector: 0.3 X0

Interaction point

2009-06-03 Junjie Zhu 17

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SLIDE 18

Calorimeter calibration (I)

Calorimeter calibration: ADC → GeV Electronics calibration using pulsers:

φ

inject known electronics signal into preamplifier and

equalize readout electronics response

φ intercalibration for both EM and HAD calorimeters φ-intercalibration for both EM and HAD calorimeters Unpolarized beams at the Tevatron Energy flow in the transverse plane should not have any

η

Energy flow in the transverse plane should not have any

azimuthal dependence

Use inclusive EM and jet collider data

Red: average Black: one cal tower

Use

c us e a d jet co de data

Layer 1 Layer 1 Layer 2 Layer 2

Before φ-intercalibration After φ-intercalibration

Layer 3 Layer 4 Layer 3 Layer 4 2009-06-03 Junjie Zhu 18 Layer 3 Layer 4 Layer 3 Layer 4

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SLIDE 19

Calorimeter calibration (II)

η-intercalibration for both EM and HAD calorimeters EM: Use Z→ee events

φ

HAD: Use γ+jet and di-jet events

EM lib ti t t EM calibration constants

η Results from two different running periods

2009-06-03 Junjie Zhu 19

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SLIDE 20

Calorimeter calibration (III)

Electrons lose ~15% of energy in front of the calorimeter Amount of dead material determined using electron EMFs Exploit longitudinal segmentation of EM calorimeter Fraction energy depositions (EMFs) in each EM layer are sensitive

to the amount of dead material to the amount of dead material

Amount of missing material in the Geant MC simulation:

(0.16 ± 0.01) X0 Electron EMFs Red: Electron EMFs Red: data Black: simulation

2009-06-03 Junjie Zhu 20

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SLIDE 21

Calibration results

EM resolution Before σ=3.35 GeV After σ=2.10 GeV

2009-06-03 Junjie Zhu 21

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SLIDE 22

Calibration results

EM resolution Before σ=3.35 GeV After σ=2.10 GeV 0.0<|η|<0.4 HAD resolution 0.4<|η|<0.8 Before Before After After

2009-06-03 Junjie Zhu

After

22

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SLIDE 23

Parameterized MC simulation

Interfaced with latest MC event generators (ResBos+Photos) Detector simulation: Electron simulation, Recoil system

simulation, Correlations between electron and the recoil system

Mass templates generation Make sure we understand Z events before we look at W events

2009-06-03 23 Junjie Zhu

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Parameterized MC simulation

Interfaced with latest MC event generators (ResBos+Photos) Detector simulation: Electron simulation, Recoil system

simulation, Correlations between electron and the recoil system

Mass templates generation Make sure we understand Z events before we look at W events Central value blinded until the analysis was approved by D0 Cl

t t d i f ll MC i l ti

Closure test done using full MC simulation

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Doing a blind analysis does not mean doing an analysis blindly...

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SLIDE 25

Mass fits

Z invariant mass (Mee), 18k W transverse mass (MT), 500k MZ = 91.185 ± 0.033 (stat) GeV MW = 80.401 ± 0.023 (stat) GeV

Z

( ) (WA MZ=91.188 ± 0.002 GeV)

W

( )

2009-06-03 25 Junjie Zhu

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SLIDE 26

Mass fits

pT(e)

MW = 80.400 ± 0.027 (stat) GeV

pT(ν)

M 80 402 ± 0 023 ( t t) G V

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MW = 80.402 ± 0.023 (stat) GeV

Junjie Zhu

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SLIDE 27

Uncertainties

2009-06-03 27 Junjie Zhu

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SLIDE 28

W boson mass

Use BLUE method to combine three

results esu ts MW=80.401 ± 0.043 GeV

Most precise measurement from one

p single experiment to date

Expect the Tevatron combined

uncertainty to be smaller than the LEP combined uncertainty for the first time first time

Expect the world average uncertainty

to be reduced by ~10%

Expect the upper limit on the SM

Higgs mass to be reduced by ~ 5 GeV

Expect ΔMW=15 MeV for the ultimate

Tevatron MW uncertainty

2009-06-03 28 Junjie Zhu

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SLIDE 29

Backup Slides

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SLIDE 30

Higgs mass constraints (2009)

2009-06-03 30 Junjie Zhu

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SLIDE 31

Calorimeter calibration

CDF calibration: Use J/ψ→μμ, ϒ→μμ, Z→μμ to calibration the tracking system Use E/p distribution for electrons from W decays to calibrate the

calorimeter system

D0 calibration: D0 calibration: Worse tracker momentum resolution Only ~20k Z→ee events

  • y

2

Similar electron pT distributions for Z and W events

2009-06-03 Junjie Zhu 31

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SLIDE 32

η-equalization and absolute EM scale

O φ d f f d i li i t d Z t Once φ degree of freedom is eliminated, use Z→ ee events to absolutely calibrate each φ-intercalibrated η ring Reconstructed Z mass: ) cos 1 ( 2 ω = E E m Reconstructed Z mass: The electron energies are evaluated as: ) cos 1 ( 2

2 1

ω − = E E m

Raw energy measurement from the calorimeter P t i d l ti

) , (

) 2 ( 1

θ

raw raw

E K E E + =

Raw EM cluster energy:

the calorimeter Parameterized energy-loss corrections from Geant MC simulation

'

E C E

i raw

⋅ Σ = E C E

i cells

Σ

η

One (unknown) calibration Cell energy after electronics calibration, φ it lib ti d li i ht

Determine the set of calibration constants Ciη that

constant per η ring φ-nitercalibration and sampling weights

iη

minimize the experimental resolution on the Z mass and give the correct (LEP) measured value

2009-06-03 Junjie Zhu 32