W Production and Mass at the Tevatron

1
W Production and Mass at the Tevatron
Oliver Stelzer-Chilton University of Toronto

• on behalf of the CDF and DØ Collaborations

XIX Rencontres de Physique de La Vallée d'Aoste,
La Thuile, Aosta Valley, Italy, Feb 27 Mar 5
2005
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Outline

1. W Physics at the Tevatron
2. W Production Cross-Section at the Tevatron
3. W Width
4. W Charge Asymmetry
5. W Mass
6. Summary/Outlook

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W Boson Physics at the Tevatron

• Z properties known to very high precision from
  LEP
• Goal
• Match precision measurements for charged EWK
  carriers
• Tevatron is for the next few years the only
  accelerator that can produce Ws directly

Test of Standard Model
Constrain Higgs Boson
W cross section
W mass
W width
W charge asymmetry
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W Boson Production at the Tevatron
Use clean W production signatures (leptonic
decays)
Muon channel
Electron channel
Isolated, high pt lepton with large missing
transverse momentum
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CDF and DØ at the Tevatron

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

CDF

• CDF and DØ are running well
• Tevatron delivered 800 pb-1
• Peak luminosities gt 11032/cm2/s
• high luminosity upgrades
• (trigger/DAQ) finalized and on
• schedule

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Inclusive Cross-Section at
the Tevatron
2874

• Overall good agreement with the NNLO
  calculations
• Accuracy limited by the systematic effects
• Uncertainties (6) dominated by luminosity
  measurements (correlated)
• Other systematics dominated by PDF uncertainties
  (2)

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Lepton Universality in W Decays
From the measurements of the W ? e? and W ? µ ?
cross sections obtain cross section ratio U
G(W-gtµv)


?.Br(W-gtev)
G(W-gtev)
Many systematic uncertainties cancel out
In the same way from W ? e? and W ? t ? cross
sections
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Indirect W Width
R cross section ratio measurement
CDF II (m)
Many systematic uncertainties cancel out (e.g.
luminosity)
?(pp-gtW) ??????????? ?(W-gtl?l)
R
?(pp-gtZ) ?(Z-gtll) ?(W)
Allows for an internal consistency check of the
Standard Model with direct G(W) measurement
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Direct W Width

• DØ summer 2004, 177pb-1
• Measurement in W-gte? channel
• Normalization 50ltMTlt100 GeV/c2
• 625 events 100ltMTlt200 GeV/c2

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W Charge Asymmetry
Use Ws to probe the proton structure
production asymmetry in ppbar-gtWX
is sensitive to u/d

• identification of the lepton
• charge is the key
• misID probability 4 at
• ? 2

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W Charge Asymmetry

• Observable quantity is electron rapidity
• Convolution of W production asymmetry and V-A
  decay

Bin data in PT (2 bins) to increase sensitivity
Submitted hep-ex/0501023
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W Mass Measurement
Precision of direct measurements
x
x
x
x
x
x
1983 UA1 5 GeV
W mass now known to better than 5 parts in 10,000
CDF 79 MeV DØ 84 MeV
Looking forward Tevatron Run 2 has now 6 times
Run 1 CDF, DØ data sets CDF has analyzed first
200 pb-1 of data and determined uncertainties
Momentum scale measured to better than 3 parts
in 10,000
u
Hadronic recoil understood to better than 50 MeV
First Run 2 W mass measurement coming soon
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Outline W Mass Measurement
W mass is extracted from transverse mass
distribution
Two important analysis components
Detector Calibration
Fast Simulation

• NLO event generator
• Model detector effects

• Calorimeter energy scale
• Tracking momentum scale

W Mass templates
Data
Backgrounds
Binned likelihood fit
W Mass
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Run 2 W Mass Status

• 200 pb-1 of data analyzed
• First-pass of analysis complete, uncertainties
  determined
• Cross-checks ongoing
• W mass fit results blinded with hidden offset

Production and Decay Model Uncertainties
CTEQ6
MeV
WGRAD
RESBOS
CDF RUN II PRELIMINARY
Constrained by Run 1 pT(Z) measurement
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Run 2 Momentum Calibration
Set momentum scale using J/? and ?(1S) decays to
muons
momentum scale measured to 3 parts in 10,000
CDF RUN II PRELIMINARY
?MW 25 MeV
?p/p
J/? mass independent of muon PT
Upsilon mass consistent using beam-constrained or
non-beam-constrained tracks
lt1/pT(m)gt (GeV-1)
CDF RUN II PRELIMINARY
CDF RUN II PRELIMINARY
mµµ (GeV)
mµµ (GeV)
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Run 2 Energy Calibration
CDF RUN II PRELIMINARY
E/p (W?e?)
Correct for non-linearity
?MW 25 MeV
CDF RUN II PRELIMINARY
CDF RUN II PRELIMINARY
E/p (W?e?)
ET (GeV)
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Run 2 Z Mass Cross Check
Use Z mass fits for tuning and cross-checks

• Tuning
• Tracking hit resolution
• Recoil Model

• Cross-check
• Energy scales
• QED FSR

Electrons
Muons
CDF RUN II PRELIMINARY
?MZ112 MeV
CDF RUN II PRELIMINARY
?MZ56 MeV
mµµ (GeV)
mee (GeV)
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Run 2 Recoil Measurement
Measure hadronic recoil by summing over all
calorimeter towers Remove towers with energy
deposited by lepton
CDF RUN II PRELIMINARY
438 1243 92
9 MeV
Estimate removed recoil energy using towers
separated in F
Removed muon towers
?MW 10 MeV
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Recoil Model
Parametrize hadronic response
utrue given by pT(Z)
?MW 20 MeV
Tune parameters using Z events
Resolution at low pT(Z) dominated by
underlying event
Resolution at high pT(Z) dominated by jet
resolution
?MW 42 MeV
CDF RUN II PRELIMINARY
pT (Z?µµ)(GeV)
Model underlying event with min-bias data
(inelastic collisions)
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Recoil Check in W Events
Any bias in recoil along lepton direction (u)
causes bias in W mass

• Simulation includes
• Tower-removal correction
• Backgrounds
• Inefficiencies as function of u

Muons
CDF RUN II PRELIMINARY
Electrons
CDF RUN II PRELIMINARY
u (W?µ?)(GeV)
Means of simulation and data agree within
uncertainties
u (W?e?)(GeV)
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Backgrounds
Muons
CDF RUN II PRELIMINARY
Muons
Electrons
?MW 20 MeV
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W Mass Measurement
Muons
Electrons
CDF RUN II PRELIMINARY
CDF RUN II PRELIMINARY
mT fit
mT fit
mT(µ?)(GeV)
mT(e?)(GeV)
Good ?2/dof for fits
Fits still blinded
ET fit
pT fit
CDF RUN II PRELIMINARY
CDF RUN II PRELIMINARY
pT(?)(GeV)
pT(µ)(GeV)
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W Mass Measurement
CDF RUN II PRELIMINARY
Total uncertainty (76 MeV) already lower than Run
1 (79 MeV)

• Work in progress to reduce systematic
  uncertainty
• Recoil resolution (hard interaction)
• Passive material upstream

• Alignment of COT performed using cosmic rays
• NEW adjust COT wire position
• along the beam axis
• Charge bias reduced by factor of 3
• (consistent with no bias)

E/p (positrons electrons)/0.1
old alignment new alignment
CDF RUN II PRELIMINARY
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Summary/Outlook

• Summary
• Very successful W boson program at the Tevatron
• Inclusive cross section in agreement with SM
  expectations with
• high precision
• Competitive measurement for W width and lepton
  universality
• W charge asymmetry measurement eager to
  see new PDFs
• W mass analysis about to be completed
• Outlook
• In Run 1, ?MW and ?GW followed vL scaling
• Most systematic uncertainties scale with
  available collider data
• Theory input to production model will become
  important 1 fb-1
• In Run 2, could reach ?MW30 MeV, ?GW50 MeV with
  2 fb-1

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• Backup Slides

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Contributions to W Mass
W propagator includes H, tb, hypothetical new
particle loops
?MW 34 MeV
Precise knowledge of MW constrains SM MH, as well
as hypothetical new particles
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CDF Detector
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D0 Detector
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W/Z Cross Section Data-MC
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Cross Section Summary
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W/Z Cross Section vs vs
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W-gtt?

• Tau reconstruction
• Count tracks in 10o t -cone and
• veto tracks in 30o isolation cone
• Reconstruct p0 candidates in
• Shower Max detector
• Combined mass lt m(tau)

W?t?t 2345 in 72 pb-1 Background 26
(dominated QCD)
?BR(W?t?) 2.62 ? 0.07stat ? 0.21sys?0.16lumnb
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W Charge Asymmetry

• Corrections to extract asymmetry
• Charge misidentification rate.
• Background subtraction.
• Measured in each ? bin
• Both bias the asymmetry low
• ? dilution.

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DØ Z-gttt Cross Section
L226 pb-1

• Muon trigger
• neural network-based t ID
• cut NN gt 0.8
• S/B 1
• Z-gttt signal 914/-24

For m(tt)gt60 GeV/c2 sB(Z?tt)25216stat19syst
17lum pb ? removed sB(Z?tt)23715stat18syst
16lum pb hep/ex 0412020