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Progress Report on W and Z Cross-Section Measurements and Di-Boson Physics Studies

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In the latest meeting involving around 18 participants from 10 institutes, we discussed ongoing studies in the cross-sections for W/Z and di-boson processes. Key topics included the efficiency of electron and muon triggers, particle identification, and event selection for both 1pb^-1 and 1fb^-1 integrated luminosities. Preliminary results indicate that ATLAS will establish WW, WZ, and Zγ signals with significant confidence using early data. We focused on detailed systematic uncertainties and the robustness of reconstruction methods, including multivariate analysis for improved measurement accuracy.

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Progress Report on W and Z Cross-Section Measurements and Di-Boson Physics Studies

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  1. Current SM studies CMB

  2. Reports at last meeting • W/Z cross-section (CSC) • W-mass (CSC) • Dibosons (CSC) • Minimum bias (CSC) • W+charm

  3. W/Z cross-section electrons Around 18 people? Covering • Electron and muon trigger efficiency • Muon trigger efficiency • Particle ID and reconstruction for electrons and muons • Missing Et • Event selection with 1pb-1 and 1fb-1 • Cross-sections for Zee,mm,lldN/dy, dN/dpt muons Early results

  4. Di-bosons ~10 institutes • 10 institutes

  5. Lepton Trigger Efficiency • Evaluated with Z decay leptons • Single particle loses to geometrical gap, • multiple particles reaches 100% e25i : isolated electron ET>25 GeV mu20i : isolated muon PT>20 GeV

  6. Lepton Reconstruction Efficiency • Leptons of W, Z decay • Reconstruction efficiency of • IsEM 0x7FF with a track matching • MuID • PT distributions η distributions

  7. 9 Summary • Physicists from ten institutes contributed to Di-Boson Physics CSC note. • First draft is ready. • Analysis tools, such as BDT, are developed and tested in our studies. • With fully simulated MC events (both signal and background) • we show that ATLAS will establish the WW, WZ, Wγ and Zγsignals • with significance better than 5 with the first 100 pb-1data. • ZZ signal will be established with the first 1 fb-1integrated luminosity. • Cross-section measurements, with 5-10 fb-1 integrated luminosity, • the systematic errors will be the dominant uncertaintites. • Charged TGC sensitivity will be significantly improved with 100 pb-1 data • to the Tevatron limits; and with 30 fb-1 data it is orders of magnitude • improvement to LEP/Tevatron. • Neutral TGC sensitivity will be much tight compared to the limit • from LEP and Tevatron for 1 fb-1 data.

  8. Z-asymmetry • Small number of people • Looking at forward electron reconstruction

  9. Method • Multivariate analysis • Inputs variables • Topo cluster moments • +other variables • Optimal set of variables • Iterativemethod • Discriminanteanalysis • Distinguishtwoetabins : EMEC (2,5<||<3,2) and FCal (3,2<||<4,9 ) • Signal and background: • Full sim. (CSC) • Electrons from Z->ee • Jets QCD page11 M. Aharrouche SM meeting

  10. FCal EMEC bkg. signal CELLMAXFRAC CELLMAXFRAC SECONDLAMBDAN SECONDLAMBDAN LONGITUDINAL LONGITUDINAL Variables Fraction of the energy in the most energetic cell Moment of order 2 M(di)of the distance diof each cluster cell i to the shower center Ma(di)/ [Ma(di)+Mb(di)] Condition a: distance of the two most energetic cells = 0 Condition b: distance of the two most energetic cells= 10cm and the distance of the other cells = 0 page12 M. Aharrouche SM meeting

  11. Iterative Method • Principle: • At each step i, the combination of i (in N-i) variables leading to the good efficiency for a given rejection is choosen, and the i-1 variables from the step i-1 are kept. • Step 1: energy fraction in the most energetic cell • Step 2: + variable 3 • Step 3: + variable 5 • ... FCal EMEC page13 M. Aharrouche SM meeting

  12. Discriminant analysis bkgd signal likelihood FCal EMEC page14 M. Aharrouche SM meeting

  13. Results 1.13 2e-4 2.6e-4 2.4 1.4e-4 0.9e-4 page15 M. Aharrouche SM meeting

  14. Others • W-mass • Focus detailed systematics • Energy/momentum scale and linearity • Pt(W) for pt(l) • Efficiency • Get to dMw~6GeV with 10fb-1 • Min bias – known

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