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Martina Schäfer

Z’ studies at LHC Z e + e - Martina Schäfer. Exotics meeting @ CERN. 23 J une 2004. F.Ledroit (UJF-CNRS) : DEIR Th.Müller (Universität Karlsruhe) : Diplomarbeit. IEKP. Martina Schäfer. 1. Z’ models and di scovery limits Data used Kinematics DY and Interference

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Martina Schäfer

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  1. Z’ studies at LHCZe+e- Martina Schäfer Exotics meeting @ CERN 23 June 2004 F.Ledroit (UJF-CNRS) : DEIRTh.Müller (Universität Karlsruhe) : Diplomarbeit IEKP Martina Schäfer 1

  2. Z’ models and discovery limits • Data used • Kinematics • DY and Interference • Electron identification • Calibration • Z’ reconstruction in full sim • Background • Total decay width • Leptonic cross section • A_FB • Summary and outlook discriminating variables Martina Schäfer 2

  3. Z’ models (1) The research for Z’ bosons is motivated by the high number of models beyond the standard model that propose extra gauge bosons. As it is a channel easy to observe, this channel is an excellent method to distinguish the models. • SSM • Z’ with same couplings as the usual Z boson • E6 models • Effectif rang 5 models • Based on GUTS, popular extensions: SO(10) and E6 • E6SO(10) x U(1)SU(5)xU(1)x U(1)MSxU(1)ß • Z’=sinß Z + cosß Z • studied: Z, Z et Z Martina Schäfer

  4. Z’ models (2) • tower of Kaluza-Klein resonances for all gauge bosons withM²n=(nMc)²+M0², (Mc compactification scale, M0 mass of the ordinary gauge boson) • LR symmetric models • SU(2)LxU(1)Y (SM) enlarged to SU(2)LxSU(2)RxU(1) • =gL/gR: ration of the couplings of the left and the right gauge bosons • studied:  =1 • Z’(KK): extra dimensions • fermions confined on a 3-brane, gauge bosons propagate with the gravitation in the extra dimensions (small, orthogonal to the branes) • here: one extra dimension compactified on S1/Z², all fermions are on the same « orbifold point » MC=1TeV n=3 n=1 n=4 n=2 goal: study of discriminating variables Martina Schäfer

  5. Discovery limits Direct and indirect discovery limits • SSM • >1.5TeV indirect, >690GeV direct • E6 models • >350..680GeV indirect, >590..620GeV direct • LR symmetric models • >860GeV indirect, >630GeV direct • Z’(KK) • 4TeV Mixing between Z’ and Z negligible Martina Schäfer

  6. Data used • channel Z’  e+e- • low lumi, without pile-up,… • generation with Pythia (within Athena) • Z’ at 1.5TeV and 4TeV with complete interference structure(DY) • DY only • without ISR/FSR • cut CKIN(1) = 1000GeV / 2500GeV • fullsim (DC1) • Z’ at 1.5TeV with DY (4TeV not yet done) • DY only • with ISR/FSR • cut CKIN(1) = 500GeV • single electrons, photons and dijet for electron identification and calibration from DC1 Martina Schäfer

  7. Kinematics for the SSM at 1.5TeV (generation level) fullsim pT of e- e+ || of e- and e+ =(e-,e+) (lab) fullsim fullsim pz of Z’ Martina Schäfer

  8. DY and interference Interference : SSM (generation level) peak Interference : Z’(KK) broader Mll(GeV) DY+Z’ narrower Mll(GeV) with int. Mll(GeV) DY destructive destructive ! Mll(GeV) with int. /GeV /GeV Martina Schäfer

  9. Electron identification • only clusters with ET>50GeV • selection • variable “ISEM” (standard electron identification ) • number of tracks (1 or 2) • number ofhits in the tracker (at least 6) • results (efficiency) • electrons (single electrons, DC1, 200GeV): 91% • electrons (single electrons, DC1, 1000GeV): 87% • photons (single photons, DC1, 200GeV ): 4% • jets (dijets, DC1, 560GeV): 0.13% Martina Schäfer

  10. Calibration • “standard” calibration : photons • de-calibration and re-calibration • only barrel • tested with single electrons (200GeV and 1TeV) Stathes Paganis (University of Wisconsin)H4e Results: Z’ (SSM 1.5TeV) electrons at  750GeV (E)/E (E=750GeV) =9.5%sqrt(E)-1  0.45%  0.6% ok (M)/M (M=1.5TeV) = sqrt(2) (E)/E  0.8% ok resolution of electrons (Z’ at 1.5TeV) /E0.7% Martina Schäfer

  11. Z’ reconstruction (1) only events with • 2 identified electrons • e+ and e- • 2 electrons in the barrel truth recalibrated resolution on the mass(1.5TeV) not recalibrated = 11 GeV + tails /E 0.7% Losts by bremsstrahlung and FSR outside the cluster neglected.  Martina Schäfer

  12. Z’ reconstruction (2) acceptance(55%, only barrel 45% ) in |cos| for different bins in |Y| high |Y| in |Y|(Y of Z’) in |cos| low |Y| Martina Schäfer

  13. Background (1) • photons and jet rejection: • see electron identification • efficiency •  90% for electrons •  0.1% for jets • 4% for photons at 1.5 TeVgeneration bb pT() << 50GeV at 1.5TeV, with B=DY, B=S=0.4, 1 year low lumi (20fb-1) Martina Schäfer

  14. Background (2) at 4 TeV, generation at 4TeV, with B=DY, B=S=0.4, 1 year high lumi (100fb-1) very clean signal Mll/GeV Martina Schäfer

  15. Discriminating variables • Total decay width • Leptonic cross section • Asymmetries Martina Schäfer

  16. Total decay width (1) ±4 peak fit for total decay width  -- generation level exemple: Z’(eta) à 1.5 TeV parton luminosity + interference BW BW*exp+exp DY only: Approximated by exp exp (DY) DY /GeV KK: NO DY Martina Schäfer /GeV

  17. Total decay width (2) [Res][BW*exp+exp] Mass resolution fit for total decay width  -- full sim natural decay width detector resolution G+G+G Resolution function: Gauss+Gauss (central peak + tails) Gauss+Gauss+Gauss(preliminary to take into account the asymmetry in the resolution/preliminary calibration) G+G Martina Schäfer

  18. Total decay width (3) M recalibrated DY 1.5TeV fit all models (generation) Mll/GeV full sim, SSM 1.5TeV Martina Schäfer /GeV

  19. Total decay width (4) Results at 1.5TeV – generation andfull sim syst  1…6% already at generation level, bigger for small  always over- estimated! stat. error Martina Schäfer

  20. Total decay width (5) Results at 4TeV – generation level /GeV Martina Schäfer stat. error

  21. Leptonic cross section (1) • Calculated with • luminosity (cross section of Pythia) • number of events in the peak without DY • in  4  • acceptance 1 (at generation) • * ( exotic Z’ decays) results at 4TeV, generation (n )/(15 )  LR 1.5TeV, generation Martina Schäfer n stat. error

  22. Leptonic cross section (2) results at 1.5TeV Martina Schäfer stat. error

  23. Forward/Backward (1) % of evts with wrong quark direction • in pp collisions there is no natural forward/backward definition q direction “forward” • q direction approximatedby Z’ direction (in general the quark is a valence quark and so faster than the antiquark from the sea) • wrong in 25% of the events • better at high rapidity Y of the Z’ parametrised by pol2 |Y| > 0.8: 10% wrong 1.5TeV, generation Martina Schäfer

  24. Forward/Backward (2) cos * distribution in the Z’ system exemple: Z’(chi) model at 1.5 TeV(generation) * = (e-,q) * = (e-,Z’) * = (e-,z-axis) • cos* is asymmetric A(true) • cos* : less asymmetric A(obs) • cos*is symmetric Martina Schäfer

  25. A_FB (1) as a function of M A_FB(M)=(N+-N-)/N N+: cos>0, in each  bin of M ! need acceptance correction ! or fit to the cos distribution in each bin of M 3/8(1+ cos2) + A_FB cos exemple: Z’(SSM) at 1.5TeV, generation real direction of the q fit  counting conclusion: Agreement between fitting and counting. Martina Schäfer

  26. A_FB (2) as a function of M exemple: Z’(psi) at 4TeV, generation fitting q direction  Z’ direction conclusion: Z’ washes the asymmetry out. Martina Schäfer

  27. A_FB (3) as a function of M counting, with(out) cut |Y|>0.8  q, without cut q, with cut  Z’, without cut Z’, with cut exemple: Z’(eta) at 1.5TeV, generation conclusion: A cut in |Y| reduces the loss in asymmetry. But: acceptance decreases with |Y|. Martina Schäfer

  28. A_FB (4) as a function of M Factor of dilution: A(obs)=D A(true), D-1=1-2eps(y) Dilution fit q fit Z’ fit 2D (dilution) Fit 2D, simple division doesn’t work as D depends on the model. conclusion: Fit in 2D works fine, eps(y) is independent of the model, but dependent of the mass. Advantage: access A(true) and not only A(obs) exemple: Z’(SSM) at 1.5TeV, full sim Martina Schäfer

  29. A_FB (5) as a function of M A(true), 4TeV generation Martina Schäfer

  30. A_FB (6) as a function of M Results (on peak) A(true) fit2D stat. error stat. error+ syst. error on eps(y) Martina Schäfer

  31. A_FB (7) as a function of Y exemple: Z’(LR) at 1.5TeV full sim A_FB(Y)=(N+-N-)/N N+: cos>0, in each  bin of Y ! need acceptance correction ! A_FB(-Y)= - A_FB(Y) exemple: Z’(eta) at 4TeV generation exemple: Z’(chi) at 1.5TeV generation Y Martina Schäfer

  32. A_FB (8) as a function of Y Choice: slope of a straight line to characterize models stat. error + syst. error on acceptance Martina Schäfer

  33. Summary and Outlook • To do : • 4TeV (fullsim) • Selection cuts (fullsim) • Background/noise (fullsim) • Discriminating • Outlook: • « Diplomarbeit » finished in September • ATLAS note • Analysis at generation level at 1.5 and at 4TeV for different models • interference • background • Study in full simulation • Electron identification • Calibration • Resolution • Discriminating variables • decay width • cross section • A_FB (dilution factor) Towards discrimination between models by global fits Martina Schäfer

  34. FIN BACK-UP Martina Schäfer

  35. Back-up (1) • Theoretical decay width • = gx² /48 (cv²+ca²) Mx (for mf=0) • gx=g/cosw, g=e/sin w • Extra dimensions • S1: y=0..2R, 0=2R • Z²: y=-y=2R-y • Fix points: 0 et  • Dilution • A_FB(obs)= (1-2eps) A_FB(true), eps: % of wrong q direction • Charge miss-identification: 3.5% Martina Schäfer

  36. Calibration (1) • “standard” calibration :photons • de-calibration • re-calibration • only barrel energy after recalib. Stathes Paganis (University of Wisconsin) before recalib. 200GeV /E=0.9% (E)/E (E=200GeV) =9.5%sqrt(E)-1  0.45%  0.8% ok Martina Schäfer

  37. Calibration (2) energy after recalib. 1TeV before recalib. /E=0.8% (E)/E (E=1000GeV) =9.5%sqrt(E)-1  0.45%  0.5% ok Martina Schäfer

  38. Calibration (3) Results on the Z’ (SSM 1.5TeV), electrons at about 750GeV (E)/E (E=750GeV) =9.5%sqrt(E)-1  0.45%  0.6% ok (M)/M (M=1.5TeV) = sqrt(2) (E)/E  0.8% ok /E0.7% resolution of electrons (Z’ at 1.5TeV) Martina Schäfer

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