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Towards Precision Measurements in the Standard Model Sector in ATLAS

Towards Precision Measurements in the Standard Model Sector in ATLAS. Interplay of detector learning phase and measurements of SM processes as the luminosity is cumulated. Atlas TDR 1999: under major revision in preparation for 2008 Corinne Goy (CNRS/IN2P3).

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Towards Precision Measurements in the Standard Model Sector in ATLAS

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  1. Towards Precision Measurements in the Standard Model Sector in ATLAS Interplay of detector learning phase and measurements of SM processes as the luminosity is cumulated. Atlas TDR 1999: under major revision in preparation for 2008 Corinne Goy (CNRS/IN2P3) LHC New Physics Signature

  2. Standard Model Measurements @14TeV • A fruitful adventure in : • insuring the grounds of the Standard Model : • sin2(W), rad cor, EW cor • PDFs • detailed knowledge of key ingredients : • Z, W, b, Top • Production mechanism • Branching Ratio → Controlled Predictions e e Tevatron p p SLAC e e e p • SM @ 14 TeV : • New energy domain • Precision Top physics • SU(2) non-abelian nature : gauge couplings • Ultimate(?) precision on MW LHC New Physics Signature

  3. A tool to understand : • Detector response to muons, electrons, gamma, jets • Improve/monitor the detector response • calibration : Z→ e+e- • alignment : Z →+- • Develop sophisticated method • b-tagging, missing Et, tau-id, multivariable analysis (NN, pdfs,boosted decision trees etc) ? LHC New Physics Signature

  4. New Phys A tool to understand a new Energy Domain • down to small x • up to higher Q2 • PDfs extrapolated Q2 (GeV) W/Z W/Z x LHC New Physics Signature

  5. High-pT QCD jets W, Z production gluon-to-Higgs fusion (light) { New φ squarks, gluinos (m ~ 1 TeV) First & Ultimate Background for New Physics LHC New Physics Signature

  6. LHC : some numbers • Startup Conditions /Commissionning (2008 ….) • beam crossing: 75ns or less • luminosity from 1031 to 1032 • pile-up negligeable • ~ 2009 conditions • evolving to nominal conditions • crossing angle • designed beam crossing: 25ns • luminosity: ~1033 • pile-up • Onwards • nominal conditions →O(100 pb-1) →O(10 fb-1) LHC New Physics Signature

  7. ATLAS ● 2T Solenoid for inner tracker ● Tracker: silicon (pixel + strips) and TRT (||<2.5) ● Sampling calorimetry (||<4.9) ● Toroid system for muons LHC New Physics Signature

  8. |h|<2.5 xf(x,Q2) x Z and W production • Expected large production : • systematics are rapidly a potential limitation • Production Mode • small x • gluon PDF : the least known • NNLO / DGLAP extrapolation at small X LHC New Physics Signature

  9. Some Plots • Typical W Selection: • e-ID • Ptl=e, > 25 GeV • |ηl | < 2.5 • Pt > 25 GeV • no jet with Pt>20 GeV • hadronic recoil < 30 GeV • Typical Z Selection • opposite charge Muon Track • Pt > 15 GeV, 25 GeV • Isolation • |η | < 2.5 W→e/ 50 pb-1 ATLAS preliminary in preparation Z → +- / 10 pb-1 • Clean Signal : • efficiency → PDF • calibration → Uniformity • isolation → SUSY events LHC New Physics Signature

  10. e ATLAS preliminary in preparation Tag&Probe efficiency • Efficiency from Data: • Z→ e+e- , Z →+- • reduced reliance on MC • 2 sources of uncertainties • statistical • background subtraction • comparison with MC Truth • Application: • trigger • reconstruction • selection • Dominant experimental error: • ~ 1% @ 50 pb-1 (stat) • overlap region ATLAS preliminary in preparation Electron selection efficiency in |η| and Pt bins. LHC New Physics Signature

  11. e-rapidity e+ rapidity CTEQ61 CTEQ61 MRST02 MRST02 ZEUS02 ZEUS02 ds(We)/dy Generated Generated y ds(We)/dy Reconstructed Reconstructed y PDFs • Sensitivity to PDf not degraded after detector response • up to 8% on diff cross-section • Improvement if experimental systematic error less than 4 % • achievable • Proof of principle : • 100 pb-1 simulated W data • gluons parameter uncertainty reduced by 35% [ xg(x)= x-λ ] hep-ex/0509002 LHC New Physics Signature

  12. Overall uniformity 0.7% Number of Z  ee events Example: Ecal Calibration/Uniformity • About a 12-18 months to reach nominal performance Uniformity necessary for H →γγ LHC New Physics Signature

  13. e from Z decays 0.45 fake electrons in QCD sample events Example: Isolation a powerful tool Z->e+e- (σ(QCD) = 2 mb) But in real condition control of : • Electronic Noise • Physics dependance : Bremstrahlung • Eta/Phi dependance • Underlying Events modelling • Machine Noise / Pile-up Example: Et>15GeV + η<2.5 + isolation Isolation = Econe (blue) /Ecluster(red) (normalised) • At the end a tool to clean new (other) physics signature: • Z+jets • SUSY events LHC New Physics Signature

  14. pp -> W/Z + Jets / γ+ Jets • QCD Studies • An application of Isolation criteria (trigger/offline) & sophiscated method 100 pb-1 ATLAS preliminary in preparation + Multivariable analysis • Relevant background for many new particles searches, top physics studies • First step in reducing jet energy scale uncertainties : • - recoil to Z/γ mass γ+jets measured calib JES : 2-3% LHC New Physics Signature

  15. 100 pb-1 M(3jets) GeV A needless motivation for TOP Physics @LHC Top in the Standard Model: The heaviest known particle The least known – limited by statistics of Tevatron A top factory: 106 events per fb-1 early data, no b tagging 4 jets pT> 40 GeV Isolated lepton pT> 20 GeV  trigger pTmiss > 20 GeV LHC New Physics Signature

  16. TOP Physics (cont’) hep-ex/0403021 M_W Top • (Final) Jet Energy Scale: • - W mass constraint • B tagging: • - Event fully reconstructed • Precision Top Physics: • mass +/- 1 GeV (ultimately) seems feasible. • b jet scale. 1 fb-1 LHC New Physics Signature

  17. g g W+ Z0 W+ Z0 W+ Z0 W+ Z0 & g W- Z0 W- T (and more) GC Effective couplings independent of underlying theory See Detailed Talk by Alan Wilson ATLAS-PHYS-2002-022/023 / LEP WG Fake gamma rate Tails’ description ATLAS preliminary in preparation LEPEWWG/TGC/2005-01 Neutral TGC : 0 in SM With 100 fb-1: sensitivity to 10-3 to 10-4 Tevatron ~ 10-1 to 10-3 / Weak LEP limit LHC New Physics Signature

  18. [%] e-  q q e+ Determination of sin2θW(MZ2) • Z decay asymmetric : • AFB = b { a - sin2θW( MZ2 ) } a, b calculated to NLO QED and QCD • Selection : • at least 1 electron in central region > charge • PT > 20 GeV • Mass window MZ±6 GeV • Missing Et cut < 20 GeV LHC New Physics Signature

  19. sin2(W) (cont’) • Systematic due to PDF • under more complete study • effect of Higher Order World average error: 1.6x10-4 ATLAS preliminary in preparation syst = maxValue-minValue= 7.6e-4 (worst case) • Electron in Forward region : • etmiss • new phys signature 2.5<||<3.2 3.2<||<4.9 fake electrons LHC New Physics Signature

  20. THEprecision measurement: MW • Current error : • CDF Run II : 48 MeV • WA : 25 MeV • Aim : MW < 15 MeV • Observables sensitive to MW • Lepton Transverse Momentum • Transverse Mass • Sensitivity from the Edge : • Energy Scale • Resolution • QED rad • Background: • Pileup • Underlying events • Acceptance : • PDFs |ηl | < 2.5 LHC New Physics Signature

  21. LEP : ~4.106 Z / exp Exemple : Energy Scale • Systematics controls from the (huge) Z sample: • precise Mass (LEP) : 2. 10-5 • similar production mechanism • similar phase space • Additional data sets: E/p Δ resolution ΔEnergy Scale Template dist. current estimate on δMW from the energy scale a factor 3 smaller than 15 MeV in TDR99 LHC New Physics Signature

  22. Conclusions : The Ground to New Physics Solid Grounds for New Physics Should be Established LHC New Physics Signature

  23. 1 fb-1 Unless ! Di lepton (electron) spectrum Z’e+e- with SM-like couplings LHC New Physics Signature

  24. Anyway a lot to learn from SM at the end LHC New Physics Signature

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