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 dataAFTER 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 = ±.046 for the ZEUS PDF before including this pseudo-data. It becomes λ = ±.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 : W+ -> e+ |  | >1 : W- -> e- |  | <1 : W- -> e- |  | >1 : 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

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| 25 GeV  Neutrino Pt > 25 GeV  No reconstructed jets in the event with Pt>30 GeV  Recoil 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| 25 GeV  Missing Et > 25 GeV  No reconstructed jets in the event with Pt>30 GeV  Recoil 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=1500 all 2 -> 2 processes involving q,q,g _ Also 1M Signal events: W -> e  with 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 Signal e + No Cutse - No Cuts e + All Cutse - All Cuts Signal: W -> e  CTEQ6.1   W ->  Z -> e - e + Z ->     QCD    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 E t > 25 GeV –E/p < 2 (bremsstrahlung rejection) –|  | < 2.4 –Look for the Charged Electromagnetic Pair with inv. mass M ee closest to the M Z –Select only events in which 70 GeV < M ee <110 GeV –Tag charge of the best reconstructed leg of the Pair (1 st leg) [n. of hits selection] Look if the charge of the 2 nd leg is the same as the 1 st leg Charge Misidentification Real Data Analysis Simulation Charge Misidentification 1 st Leg 2 nd Leg Z0Z0 e >0 e >0 ? M Z [GeV]

Charge Misidentification W->e Rome Sample MC-Truth Check   F-F- F+F+ In agreement with the Z->ee data-like analysis

Charge Misidentification Z->ee Rome Sample MC-Truth Check   F-F- 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 A RAW = Measured Asymmetry A TRUE = Corrected Asymmetry F - = rate of true e - misidentified as e + F + = rate of true e + misidentified as e - F-F- F+F+   Detector Level