A few slides to summarise what Alessandro and I were up to for March 24th video meeting

1
A few slides to summarise what Alessandro and I
were up to for March 24th video meeting

• Taking for granted that W/- are good
  measurements to make- are they really good
  standard candles?
• PDF uncertainty is larger than you might have
  heard comes from low-x gluon dominantly
• Maybe we can even use early LHC data to improve
  it
• But studies have only been done at ATLFAST level,
  need trigger efficiencies as a function of
  rapidity and Pt to go further

2
Look at the lepton rapidity spectra and asymmetry
at generator level -TOP
and after passing
through ATLFAST BOTTOM Generation with
HERWIGk-factors using CTEQ6.1M ZEUS_S MRST2001
PDFs with full uncertainties
3
Study the effect of including the W Rapidity
distributions in global PDF Fits by how much
can we reduce the PDF errors?
Generate data with CTEQ6.1 PDF, pass through
ATLFAST detector simulation and then include
this pseudo-data in the global ZEUS PDF
fit. Central value of prediction shifts and
uncertainty is reduced
BEFORE including W data
AFTER including W data
1day of data-taking at low Lumi
W to lepton rapidity spectrum data generated
with CTEQ6.1 PDF compared to predictions from
ZEUS PDF AFTER these data are included in the fit
W to lepton rapidity spectrum data generated
with CTEQ6.1 PDF compared to predictions from
ZEUS PDF
Specifically the low-x gluon shape parameter ?,
xg(x) x ? , was ? -.187 .046 for the
ZEUS PDF before including this pseudo-data. It
becomes ? -.155 .030 after including the
pseudo-data
4
Event Selection Criteria for W- -gtl- nl
Atlas TDR
Cross section for pp?WX with W?l?, le,µ is 30
nb (10 time larger than Tevatron)
300M evts/y at low Lumi.

• Electrons and Muons Pt gt 25 GeV
• ? lt 2.4
• Missing Et gt 25 GeV
• To reject QCD bkg
• No reconstructed jets in the event with Pt gt 30
  GeV
• Recoil on transverse plane should satisfy ult
  20 GeV

Cuts acceptance 25 Assuming Lepton
reconstruction efficiency 90 identification
efficiency 80
Total Selection Efficiency 20
60 M Ws/y al low Lumi. (10 fb-1)
5
Rome Production W- -gt e- Sample - Full
SimulationDetector and Generator levels
Comparison(after selection cuts application)
Positron Pseudo-Rapidity
Transverse W Mass
Electron Pseudo-Rapidity
6
Detector Acceptance and EfficiencyRome W-gten
sample
7
Outlook

• W Rapidity distributions are good observables to
  constrain PDFs at LHC
• LHC can significantly constrain the gluon
  distribution
• We are not limited by statistic but by systematic
  uncertainties
• To discriminate between conventional PDF sets we
  need to achieve
• an accuracy 3 on rapidity distributions.
• Substantial agreement between AtlFast and Full
  simulation analyses.
• We are planning to fully reproduce our AtlFast
  analysis with the Full Simulation
• Explore various sources of systematic
  uncertainties detector misalignments,
• detector efficiency, backgrounds etc.

8
EXTRAS
9
Rome Production W- -gt e- Sample Full
Simulation
In collaboration with Cigdem Issever and Monika
Wielers

• Rome Production W- -gt e- Sample
• HERWIG CTEQ5L, U.E. with Jimmy
• 67K fully simulated events.
• Reconstruction with Athena v10
• Analysis based on AODs
• In the next Transparencies I am going to show
• W-gte Rapidity distributions at GEN and DET Level
• W-gte Asymmetry and Ratio at GEN and DET Level

To Discriminate PDF Sets
To possibly Minimise PDF Errors
10
Rome Production W- -gt e- Sample - Full
Simulation Generator Level for Ws
CTEQ5L PDF
W and W- Rapidity
W
W-
y
W Asymmetry
W- /W Ratio
y
y
11
Rome Production W- -gt e- Sample - Full
Simulation Generator level for e and e-
e e- Pseudo-Rapidity

• TDR Selection Cuts
• Electrons ? lt 2.4 Pt gt 25 GeV
• Neutrino Pt gt 25 GeV
• No reconstructed jets
• in the event with Ptgt30 GeV
• Recoil on transverse plane ult20 GeV

e-
e
Selection Cuts applied
h
e - e- Asymmetry
Selection Cuts applied
e- /e Ratio
Selection Cuts applied
h
h
12
Rome Production W- -gt e- Sample - Full
Simulation Detector level

• Standard Rome
• Electron Identification

e e- Pseudo-Rapidity

• TDR Selection Cuts
• Electrons ? lt 2.4 Et gt 25 GeV
• Missing Et gt 25 GeV
• No reconstructed jets
• in the event with Ptgt30 GeV
• Recoil on transverse plane ult20 GeV

e-
e
Selection Cuts applied
h
e- e- Asymmetry
e- /e Ratio
Selection Cuts applied
Selection Cuts applied
h
h
13
Background to W- -gte- ne with ATLFAST
Background Generation

• 1M W -gt tn (-gt enn) events
• with HERWIG CTEQ5L
• 1M Z -gt tt- (-gt e nn e- nn) events
• with HERWIG CTEQ5L
• 1M Z -gt ee- events with HERWIG CTEQ5L
• 600K QCD events with HERWIG CTEQ5L
• IPROC1500
• all 2 -gt 2 processes involving q,q,g

Stat too little!!
_
Also 1M Signal events W -gt en with HERWIG
CTEQ6.1
14
e- Rapidity distributions of Background vs
Signal
e No Cuts
e- No Cuts
AtlFast
Backgrounds sums
h
h
e All Cuts
e- All Cuts
h
h
15
Charge MisidentificationReal Data Analysis
Simulation

• Z -gt ee- sample from ATLAS Full Simulation
• 98K events, HerwigCTEQ5L,
• U.E with Jimmy
  
• Event Selection
• Standard Rome Electron identification
• Events with 2 or more Charged
• Electromagnetic Objects in the
• E.M. calorimeter
• Only 2 Elec.Obj. with Et gt 25 GeV
• E/p lt 2 (bremsstrahlung rejection)
• h lt 2.4
• Look for the Charged Electromagnetic Pair
• with inv. mass Mee closest to the MZ
• Select only events in which
• 70 GeV lt Mee lt110 GeV
• Tag charge of the best reconstructed leg
• of the Pair (1st leg) n. of hits selection
• Look if the charge of the 2nd leg
• is the same as the 1st leg

MZ GeV
Charge Misidentification
16
Charge MisidentificationW-gte Rome
SampleMC-Truth Check
F-
h
F
h
In agreement with the Z-gtee data-like analysis
17
Charge MisidentificationZ-gtee Rome
SampleMC-Truth Check
F-
h
F
h
In agreement with the Z-gtee data-like analysis
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Systematic Uncertainties using Full Simulation
Charge
Misidentification

• Charge Misidentification dilutes the Charge
  Asymmetry
• Correction
• Use Z -gt ee- sample from
• ATLAS Full Simulation
• Rome production
• 98K events, HerwigCTEQ5L
• data-like analysis
• (No use of MC-Truth)
• Mis-ID rate
• negligible?

Detector Level
F-
ARAW Measured Asymmetry ATRUE Corrected
Asymmetry F- rate of true e-
misidentified as e F rate of true e
misidentified as e-
h
Detector Level
F
h