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W/Z properties (ATLAS and CMS)

W/Z properties (ATLAS and CMS). Javier Santaolalla (CIEMAT-Madrid) On behalf of the ATLAS and CMS collaborations HCP Paris 14-18 Nov 2011. Outline. Introduction Inclusive boson production W/Z properties Conclusions. CMS. ATLAS. EWK studies are…. …interesting for:

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W/Z properties (ATLAS and CMS)

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  1. W/Z properties (ATLAS and CMS) Javier Santaolalla (CIEMAT-Madrid) On behalf of the ATLAS and CMS collaborations HCP Paris 14-18 Nov 2011

  2. Outline • Introduction • Inclusive boson production • W/Z properties • Conclusions CMS ATLAS

  3. EWK studies are… • …interesting for: • Measurement of SM param. • Better underst. of QCD • processes (PDFs, αS) • …important in CMS/ATLAS operation since they are useful to calibrate the detector (trigger, efficiencies, resolutions…) Gfitter http://gfitter.desy.de/Standard_Model/

  4. EWK studies are… • …also important to look for new physics • It is background of important searches • It places strong constraints on SM parameters SUSY search (Dijet+ETmiss) squarks and gluinos 3. Sensitive to new physics effects W’ search (µ channel) arXiv:1109.6572 CMS-EXO-11-024

  5. Introduction • And… • W/Z bosons copiously produced in the collisions • Leptons are easily detected (working with leptonic modes) • Channels studied • W±l±ν(l=electron,muon,tau) • Zl+l-(l=electron,muon,tau)

  6. W/Z boson selection • W signature • High momentum, isolated lepton • Large ETmiss ETmiss • W selection • Pt > 20-25 GeV and isolated • Selected by inclusive lepton trigger • Quality requirement on lepton reco and id • MT > 40-50 GeV • DY veto µ l

  7. W/Z boson selection • Z signature • Two high momentum, isolated leptons • Z selection • Two high pT isolated leptons • Quality requirement on lepton reco and id • Selected by inclusive lepton trigger • Invariant mass window ~[60,120] GeV

  8. W inclusive production (µ or e) Selection • Previous selection • MT >40 GeV and • ETmiss > 25 GeV (ATLAS) ATLAS Procedure CMS ATLAS Fit Etmiss Counting

  9. W/Z inclusive production (µ or e) JHEP 10 (2011) 132 Systematics unc. of the order of 2% (lum excluded) Systematics reduced In the ratios arXiv:1109.5141

  10. W inclusive production (τ) Charged jet with 1-prong or 3-prong plus EM energy Description • τ jet = light and collimated jet, non-0 flight distance. • τ identification: BDT with 8 variables. • EWK bkg from MC, QCD bkg from data control region Syst unc. ~23% Also preliminary results from CMS: arXiv:1108.4101 EWK-11-003

  11. Z inclusive production (τ) JHEP 08 (2011) 117 Description • 4 final states: τµτµ, τµτhad • τeτhad, τeτµ • MT and Etmiss max • Signal yield estimated with a fit to the visible mass (CMS) • Bckg yields estimated with data-driven methods (ATLAS) τlτhad • Highest BR • Biggest backgrounds: QCD, W+jets and Zµµ τeτµ τ µ τµ • Highly affected by DY • BDT in 5 kinematic variables (ATLAS) likelihood in 4 variables (CMS) • Cleanest • Additional cuts to remove Ws ant ttbar (ATLAS)

  12. Z inclusive production (τ) Description • 4 final states: τµτµ, τµτhad • τeτhad, τeτµ • MT and Etmiss max • Signal yield estimated with a fit to the visible mass (CMS) • Bckg yields estimated with data-driven methods (ATLAS) arXiv:1108.2016 Conclusions Unc. ~ 10% Agreement with SM PF: good τ id capabilities (CMS)

  13. Z rapidity distribution Procedure Large coverage using calorim. (electrons) (ATLAS&CMS) Similar measurement on the W lepton pseudorapidity (ATLAS) • Useful to constraint • PDFs • Z unc: ~ 3% barrel, • ~ 7% endcap • Event counting in each bin • QCD from data, rest of bck • from simulation arXiv:1110.4973 arXiv:1109.5141

  14. W charge asymmetry Sensitive to parton density functions ATLAS and CMS constraining the region In reasonable agreement with PDF predictions. χ2 CERN-PH-EP-2011-024 arXiv:1109.5141 CMS-EWK-10-006

  15. W charge asymmetry CMS ATLAS NNPDF Improved precision in proton PDFs thanks to LHC data on charge asymmetry arXiv:1108.1758v2, NNPDF collaboration

  16. Z momentum distribution PLB 705 (2011) 415-434 Important for W mass (<30GeV region) • Theory predicts high pT • region (pQCD) O(αs2) • (emission of hard partons) arXiv:1110.4973 • Low pT region dominated by non-perturbative QCD and tuning. Uncertainties increasing from ~ 3% (low pT) to ~20% high pT

  17. W momentum distribution (ATLAS) Fixed-order pQCD calculations Important for MW • Underestimation by NLO computations (30%) • Underestimation at intermediate pT values, by NNLO predictions • (general good agreement) arXiv:1108.6308 Parton shower + Matrix element gen • Bad agreement with MC@NLO and POWHEG • SHERPA, ALPGEN, RESBOS and PYTHIA: general good agreement Universality of strong interactions effects in W/Z production Syst. unc. ranges from 3% (low pT) to 10% (high pT)

  18. W polarization (CMS) Dominant W+jet process • At high energy, quarks are left • handed polarized • For W production in the • transverse plane, W spin • “tends” to compensate • the spin of the d quark • At very high pT, W bosons can • be considered as massless Phys.Rev.D84:034008,2011 ― f0― fL― fR • Longitudinal polarization decreases with W pT • W ~75% left polarized at very high pT • Left-handed nature of EWK interactions • prevalence of valence quarks in protons

  19. W polarization (CMS) PRL 107 (2011) 021802 Polarization fractions • Observation of polarization at LHC • Left polarization dominant, but reduced • due to kinematic effects and other • subprocesses • Variable sensitive to W polarization • Electron and muon channels

  20. Conclusions • EWK processes largely studied in CMS and ATLAS. • Interesting results to constraint PDFs, check standard model and for other studies. • Processes studied so far are in good agreement with SM prediction at this new energy scale. • More interesting results still to come • All EWK ATLAS and CMS results are available: • Atlas: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/StandardModelPublicResults • CMS: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEWK

  21. BACK UP

  22. Forward backward asymmetry • Drell-Yan cross section • AFB depends on the quark type and on sin2θW CMS-EWK-10-011

  23. Sin θW Sin θW is the only free parameter to test fermion/boson couplings • Multivariate analysis on y, inv. mass and Collins-Soper angle • EWK interactions description is taken from SM, sin θW is free • Unbinned maximum likelihood arXiv:1110.2682 23

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