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

Look at the lepton rapidity spectra and asymmetry at generator level -TOP

and after passing through ATLFAST –BOTTOM

Generation with HERWIG+k-factors using CTEQ6.1M ZEUS_S MRST2001 PDFs with full uncertainties

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

W+ to lepton rapidity spectrum data generated with CTEQ6.1 PDF compared to predictions from ZEUS PDF

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

~1day of data-taking at low Lumi

Specifically the low-x gluon shape parameter λ, xg(x) = x –λ , was λ = -.187 ± .046 for the ZEUS PDF before including this pseudo-data. It becomes λ = -.155 ± .030 after including the pseudo-data

Event Selection Criteria for W+- ->l+- l

Cross section for pp→W+X with W→lν, l=e,μ is ~30 nb (10 time larger than Tevatron) 300M evts/y at low Lumi.

Atlas TDR

Electrons and Muons: Pt > 25 GeV |η| < 2.4

Missing Et > 25 GeV

To reject QCD bkg:

No reconstructed jets in the event with Pt > 30 GeV

Recoil on transverse plane should satisfy |u|< 20 GeV

Cuts acceptance ~25%Assuming Lepton reconstruction efficiency ~ 90% & identification efficiency ~ 80%

Total Selection Efficiency ~20%

60 M W’s/y al low Lumi. (10 fb-1)

W+ -> e+ || <1 : 0.94 +- 0.03W+ -> e+ || >1 : 0.84 +- 0.02

W- -> e- || <1 : 0.97 +- 0.03W- -> e- || >1 : 0.85 +- 0.02

Signal Selection Efficiency (DET-AfterCuts / GEN-AfterCuts)

Rome Production W+- -> e+- Sample - Full Simulation

Detector and Generator levels Comparison(after selection cuts application)

Generator Level

Detector level(Full Simulation)

Generator Level

Detector level(Full Simulation)

Generator Level

Detector level(Full Simulation)

Positron Pseudo-Rapidity

Electron Pseudo-Rapidity

Transverse W Mass

Detector Acceptance and Efficiency

Rome W->e+ sample

• W Rapidity distributions are good observables to constrain PDF’s 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.

Outlook

EXTRAS

Rome Production W+- -> e+- Sample

Full Simulation

In collaboration with Cigdem Issever and Monika Wielers

• Rome Production W+- -> e+- Sample – HERWIG + CTEQ5L, U.E. with Jimmy

– ~67K fully simulated events.

– Reconstruction with Athena v10

– Analysis based on AOD’s

• In the next Transparencies I am going to show: – W->e Rapidity distributions at GEN and DET Level

– W->e Asymmetry and Ratio at GEN and DET Level

To Discriminate PDF Sets

To possibly Minimise PDF Errors

Rome Production W+- -> e+- Sample - Full Simulation Generator Level for W’s

W Asymmetry

CTEQ5L PDF

y

W-

W+

y y

W- /W+ Ratio

W+ and W- Rapidity

)(/

)(/)(

Wdyd

WdydyR

W

WW

)(/)(/

)(/)(/)(

WdydWdyd

WdydWdydyA

WW

WWW

Rome Production W+- -> e+- Sample - Full Simulation Generator level for e+ and e-

e+ - e- Asymmetry

e- /e+ Ratio

e- e+

Selection Cuts applied

e+ e- Pseudo-Rapidity

TDR Selection Cuts:Electrons: |η| < 2.4 Pt > 25 GeVNeutrino Pt > 25 GeVNo reconstructed jets in the event with Pt>30 GeVRecoil on transverse plane |u|<20 GeV

Selection Cuts applied

Selection Cuts applied

Rome Production W+- -> e+- Sample - Full Simulation

Detector level

e+- e- Asymmetry

e- /e+ Ratio

Selection Cuts applied

Selection Cuts applied

TDR Selection Cuts:Electrons: |η| < 2.4 Et > 25 GeVMissing Et > 25 GeVNo reconstructed jets in the event with Pt>30 GeVRecoil on transverse plane |u|<20 GeV

Standard Rome Electron Identification

Selection Cuts applied

e- e+

e+ e- Pseudo-Rapidity

1M W -> -> e events with HERWIG + CTEQ5L

1M Z -> -> e+ e- events with HERWIG + CTEQ5L

1M Z -> e+e-events with HERWIG + CTEQ5L

600K QCD events with HERWIG + CTEQ5L: IPROC=1500all 2 -> 2 processes involving q,q,g

_

Also 1M Signal events: W -> ewith HERWIG + CTEQ6.1

e,

W+- ->e+- l

Background to W+- ->e+- e

with ATLFAST

Background Generation:

Stat too little!!

e+- Rapidity distributions of Background vs Signale+ No Cutse- No Cuts

e+ All Cutse- All Cuts

Signal:W -> eCTEQ6.1

W ->

Z -> e-e+

Z ->

QCD

)(nbBd

dee

Backgrounds sums:

AtlFast

• Z -> e+e- sample from ATLAS Full Simulation: ~98K events, Herwig+CTEQ5L, 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 > 25 GeV– E/p < 2 (bremsstrahlung rejection)– || < 2.4– Look for the Charged Electromagnetic Pair with inv. mass Mee closest to the MZ

– Select only events in which 70 GeV < Mee <110 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

Charge MisidentificationReal Data Analysis Simulation

Charge Misidentification

1st Leg

2nd Leg

Z0

e >0

e >0 ?

MZ [GeV]

Charge MisidentificationW->e Rome Sample

MC-Truth Check

F-

F+

In agreement with the Z->ee data-like analysis

Charge MisidentificationZ->ee Rome Sample

MC-Truth Check

F-

F+

In agreement with the Z->ee data-like analysis

• Charge Misidentification dilutes the Charge Asymmetry

– Correction:

• Use Z -> e+e- sample from ATLAS Full Simulation Rome production ~98K events, Herwig+CTEQ5L data-like analysis (No use of MC-Truth)

– Mis-ID rate

negligible?

Systematic Uncertainties using Full Simulation: Charge Misidentification

FF

FFAA

RAWTRUE

1

ARAW = Measured AsymmetryATRUE = Corrected AsymmetryF- = rate of true e- misidentified as e+

F+ = rate of true e+ misidentified as e-

F-

F+

Detector Level

Detector Level