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Study of Z + Jets in the electron channel with CMS at the LHC

Study of Z + Jets in the electron channel with CMS at the LHC. Christos Lazaridis University of Wisconsin-Madison Preliminary Examination. Magnets. Superconducting NbTi magnets Operating @1.9K 1232 dipoles bend proton beam around ring, B = 8T Quadrupoles focus beam.

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Study of Z + Jets in the electron channel with CMS at the LHC

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  1. Study of Z + Jetsin the electron channel with CMS at the LHC Christos Lazaridis University of Wisconsin-Madison Preliminary Examination

  2. Magnets • Superconducting NbTi magnets • Operating @1.9K • 1232 dipoles bend proton beam around ring, B = 8T • Quadrupoles focus beam Arrows show direction of magnetic field Christos Lazaridis Preliminary Examination

  3. Christos Lazaridis Preliminary Examination Detecting Particles in CMS

  4. RCT Trigger Supervisor • An online framework to configure, test, operate and monitor the CMS Trigger • Each subsystem is represented by a “cell” • Cells communicate via XML-formatted commands My contribution so far: • A Control Panel for the RCT that permits • Specific Crate/Card selection • Command execution Crate Selection Card Selection Command Selection Christos Lazaridis Preliminary Examination

  5. Christos Lazaridis Preliminary Examination Calorimeter Trigger Algorithms:Electrons

  6. Calorimeter Trigger Algorithms:Jets • Jets • Not a “cone” but a “square” algorithm • 12x12 Trigger tower ΣET > Threshold sliding in 4x4 steps AND • Central 4x4 ET > others Christos Lazaridis Preliminary Examination

  7. Christos Lazaridis Preliminary Examination Previous Studies • LHC will probe higher Z pT shedding light on PDF uncertainties Tevatron Plots Can be used to scale the highest Jet PT • Shaded bands are uncertainties for fixed strong coupling strength and varying PDF parameters (hep-ph/0512167: Parton Distributions and the Strong Coupling: CTEQ6AB PDFs - J. Pumplin, A. Belyaev, J. Huston, D. Stump, W.K. Tung)‏

  8. Previous Studies – CDF (1)‏ • Requirements: • Two electrons with ET > 25 GeV • At least one central electron: |ηe|<1 • Second electron central or forward : |ηe|<1 or 1.2 < |ηe|<2.8 • Z mass window: 66 < Mee < 116 GeV/c2 • ΔR (e,jet) > 0.7 • Jets found using the MidPoint algorithm with R=0.7 • pTjet > 30 GeV/c and |yjet| < 2.1 Mee Invariant Mass Events with at least one jet CDF Public Note 8827 Christos Lazaridis Preliminary Examination

  9. Previous Studies – CDF (2)‏ Z + Jets Inclusive Cross Section MCFM: Monte Carlo for FeMtobarn processes Data/Theory Ratio • Shaded bands show systematic uncertainties • Dashed lines: PDF uncertainties • Dash-dot lines: scale uncertainties CDF Public Note 8827 Christos Lazaridis Preliminary Examination

  10. Previous Studies – CDF (3)‏ CDF has found two Z+4 Jet events in 1.7 fb-1 of data CDF Public Note 8827 Christos Lazaridis Preliminary Examination

  11. Christos Lazaridis Preliminary Examination Trigger on Electrons for Z + 0-5 jets Automatic L1 trigger for electrons above 63 GeV max value of 63 GeV Isolated Electron Et

  12. Christos Lazaridis Preliminary Examination Highest Et Reconstructed Electrons Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets • Electrons with: • Et > 15 GeV • -2.4 < η < 2.4

  13. Christos Lazaridis Preliminary Examination Highest Et Electrons η/φ Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets η1st η2nd φ1st φ2nd

  14. Christos Lazaridis Preliminary Examination Electron Finding Efficiency Entries: Overflows: 141530 135 Matched MCe 185 All MCe

  15. Christos Lazaridis Preliminary Examination Electron Finding Efficiency (2)‏ No match

  16. Christos Lazaridis Preliminary Examination Z Invariant Mass We can “see” a Z masspeak even with 5 Jets! • 2 isolated electrons with Pt > 25 GeV • -2.4 < η < 2.4 • Z+0 Jets fit: • Range 80-100 GeV Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets Z+4 Jets Z+5 Jets

  17. Christos Lazaridis Preliminary Examination Reconstructed Pt(Z)‏ Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets Z+4 Jets Z+5 Jets Verify theory by comparing data with theoretical predictions that depend on PDFs

  18. Christos Lazaridis Preliminary Examination Jet Reconstruction Algorithm • Iterative cone • Draw a cone ΔR around a seed with Et > threshold • The computed direction seeds a new cone • Iterate until the cone position is stable • Stable cone ≡ a jet; towers are removed from the list of input objects • no jet merging • Pythia creates these using the Lund string model R

  19. Christos Lazaridis Preliminary Examination Highest Et Jets Second Jet Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets • Iterative Cone • Rcone = 0.5 • Pt > 15 GeV • uncorrected • -2.4 < η < 2.4 • Some jets (e.g. in Z+0 jets events) are underlying soft QCD radiation Highest Jet

  20. Christos Lazaridis Preliminary Examination Highest Et Jets η/φ Z+0 Jets Z+1 Jets Z+2 Jets Z+3 Jets η1st η2nd φ1st φ2nd

  21. Christos Lazaridis Preliminary Examination Summary/Future Plans • Z + Jets is a diverse channel... • Calibration (Important at LHC startup!)‏ • Study as background (Higgs & SUSY studies)‏ • More Monte Carlo studies need to be done • Study efficiencies, Triggers • While doing all the above, work on the RCT

  22. Christos Lazaridis Preliminary Examination Backup Slides

  23. Christos Lazaridis Preliminary Examination Higgs • Standard electroweak theory predicts W± and Z of zero mass • Experiment tells us that the weak force is short-range, so its carriers must be massive • The Higgs field gives mass to these three bosons by spontaneously breaking the SU(2)xSU(1) symmetry • The Higgs coupling to other particles determines their masses • Stronger coupling  Higher mass • Couples to self • Small problem: • Theory cannot predict the Higgs mass

  24. Christos Lazaridis Preliminary Examination Expected Higgs Mass • LEP results from a direct Higgs search set a limit on the Higgs mass ~115GeV/c2 • On January 2007, indirect Tevatron evidence were predicting mH=85+39-28 GeV/c2

  25. Christos Lazaridis Preliminary Examination General Higgs Production • Vector boson fusion • Lower rate • Lower background • Gluon-gluon fusion • Highest Higgs production rate • High QCD background Associated W/Z production ttbar fusion

  26. Christos Lazaridis Preliminary Examination Muon System • Muon chambers identify muons and provideposition information for track matching • Drift Tubes in the central barrel region • Cathode Strip Chambers in the endcap region • Resistive Parallel Plate Chambers in both the barrel and endcaps

  27. Calorimeter Trigger Algorithms:Electrons • Electron (Hit Tower + Max)‏ • 2-tower ΣET + Hit tower H/E • Hit tower 2x5-crystal strips > 90% ET in 5x5 (Fine Grain)‏ • Isolated Electron (3x3 Tower)‏ • Quiet neighbors: all towers pass Fine Grain & H/E cut • One group of 5 EM ET < Threshold Christos Lazaridis Preliminary Examination

  28. Christos Lazaridis Preliminary Examination Removing Electrons From Jets Collection • Keep jets that don’t have a nearby “electron” within a cone ΔR<0.15… Keep >0.15 …where “electron” is required to havethe ratio 0.85< Pt,electron/Pt,Jet < 1.15

  29. Lund String Fragmentation • Used by PYTHIA to describe hadronization and jet formation • Color “string" stretched between q and qbar moving apart • String breaks to form 2 color singlet strings until only on mass-shell hadrons remain Christos Lazaridis Preliminary Examination

  30. Z Production: Rate   • At 1033: • ~108 events/10fb-1 Z (50 Hz - 500Hz for full luminosity)‏ • Z+jet: ~ 0.1 Hz • Z production ~2.5nb • More stuff here   (nb)‏   Events/sec ( L = 1033 cm-2s-1)‏       s 10 1 √s (TeV)‏ Christos Lazaridis Preliminary Examination

  31. Christos Lazaridis Preliminary Examination

  32. Christos Lazaridis Preliminary Examination

  33. Christos Lazaridis Preliminary Examination Previous Studies D0 (1)‏ • hep-ex/0506025 – A. Bellavance • hep-ex/0608052 – V.M. Abazov et. al. • Tevatron D0 Results • 1.96 TeV ppbar collisions • Z → e+e- selection cuts: • 2 electromagnetic objects • ET > 25 GeV • Pseudorapidity η< |1.05| (central calorimeter only)‏ • Jets Identification: • Cone Algorithm • ET > 20 GeV • η < |2.4|

  34. Christos Lazaridis Preliminary Examination Previous Studies D0 (2)‏ D0 (0.4fb-1) Cross Section vs Jet Multiplicity MCFM: Monte Carlo for FeMtobarn processes ME-PS: LO Matrix Element calculations using Pythia for parton showering Pythia predicts fewer events at high jet multiplicity because of missing higher order contributions at the hard-scatter level

  35. Christos Lazaridis Preliminary Examination Previous Studies D0 (3)‏ D0 (0.4fb-1) Highest pT jet distribution ME-PS: LO Matrix Element calculations using Pythia for parton showering Z/γ* + ≥ 1 jet Z/γ* + ≥ 2 jets Z/γ* + ≥ 3 jets

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