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Exploring W Polarization and Top Spin Correlation in ATLAS: Progress and Results

This document presents recent findings on W polarization measurement and top spin correlation (TSC) from the ATLAS experiment, discussing the methodologies employed in semi-lepton and di-lepton channels. The preliminary analysis of data collected in 2011 shows significant insights into top properties and potential new physics. The studies incorporate advanced techniques for event reconstruction, background management, and polarization fitting, highlighting the current progress and future steps towards increased precision in measuring top quark behaviors.

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Exploring W Polarization and Top Spin Correlation in ATLAS: Progress and Results

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  1. W polarization & Top Spin correlation Liming CHEN, Bo LI, Emmanuel MONNIER, Lian-You SHAN, Chengguang ZHU FCPPL5, Mar 21, Orsay ( Many thanks to the organizers )

  2. Outline • Introduction • W polarization measurement • Semi-lepton channel • Di-lepton channel • Top spin correlation measurement • Summary L.Y. SHAN @ W&top polarization

  3. Introduction • “top property group” in ATLAS • CPPM, SDU, IHEP in competing with • Gottingen, LIP, • 1.04/fb 2011 data analyzed • Note prepared • 4.7/fb analysis in progress • spin correlation in preparation L.Y. SHAN @ W&top polarization

  4. Intro to the physics • Possible new physics in twb coupling • Possible new physics via top pair production • Gluon contributions, NLO QCD, EW loops • Virtual contribution from New physics like SUSY … ? • Backgrounds : W+jets, multi-Jets, single top L.Y. SHAN @ W&top polarization

  5. Intro to the analyses • EF_e20_medium/EF_mu18 • EF_e22vh_medium1 • EF_mu18_medium • Leptons : • PS : pT, | • Tight_PP / muID_combined • Isolation : Etcone & pTcone /dR_jet • Jet • pT, |, JVF > 0.75 • AntiKt4_EMTopo • B jet • JetFitterCOMBNN/MV1 (0.602) • 2 b jet required • MET : RefFinal_em_tightpp • defined & utilized w t : The angle between lepton direction in W ( top ) rest frame and W ( top ) direction in top ( ttbar ) rest frame L.Y. SHAN @ W&top polarization

  6. W polarization measurement • Event reconstruction • Pick 2 from ≥ 2 light jets for • pick 1 from ≥ 2 b jets for • pick another b closest to lepton (smallest ) • Solve neutrino from • KLFitter as a cross check • Breitwigners against JetEnergy/MET resolution • Tagged b is necessary • Corrections from Performance groups L.Y. SHAN @ W&top polarization

  7. W-pola Yields ele muo • W+jet : 2-b tag MC-effi multiplied to DD scale • Mjets : DD-extracted faking multiplied to loose-control • Others : MC simulation L.Y. SHAN @ W&top polarization

  8. W-pola fit • Unfolding method • Each 1/3 polarization has its own response • 3 PROTOS samples simulated/prepared • Unfolding function extracted for each polarization • Fit data with • Response functions convoluted • Backgrounds shapes superposed • Consistency from Iterating procedure L.Y. SHAN @ W&top polarization

  9. W-pola result SM 0.695 0.304 Dominant uncertainty In addition to ATLAS-Conf notes, The Editor Board has approved the paper draft on 1/fb result L.Y. SHAN @ W&top polarization

  10. W-PolA di-lepton • Extra backgrounds : Z+jets, di-boson • >15GeV, |-91GeV|>10GeV • Tagged b ≥ 1 for more yields • A little difficulty in Event topology • 2 components of MET • 2 mass of W, 2 mass of tops • Numerical searching/scanning • Many set of solutions from 2 quadratic equations • 73% success L.Y. SHAN @ W&top polarization

  11. Di-lep DISTRIBUTION L.Y. SHAN @ W&top polarization

  12. Preliminary di-lepton 380/3139/1045 events in ee/em/mm channel Systematics in progress, many thanks to Liming CHEN L.Y. SHAN @ W&top polarization

  13. Top spin correlation(TSC) • Share many with W pola analysis • Objects/event selection • Event topology reconstruction • Angles Product instead of Double differentials • Linear term contribute null once well-corrected and integrated over PS • QCD conserve parity, other contribution is small/negligible , ignore B terms • C = -9 < > • Iterated fit against unfolding function • The Mixing between the correlated and UNcorrelated samples L.Y. SHAN @ W&top polarization

  14. Angle product dIST About 3500 ele events About 500 Muo events • C = 0.42 ( SM 0.32 ) • Systematics ongoing, many thanks to Bo LI L.Y. SHAN @ W&top polarization

  15. Summary • Good progress • Work more for better precision • Thanks ! L.Y. SHAN @ W&top polarization

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