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Importance of W+jets Analysis at the LHC

This article discusses the significance of studying W+jets at the Large Hadron Collider (LHC). It explores the role of W+jets as a signal for measuring Electroweak Interaction, testing theoretical calculations, and calibrating detectors. The article also highlights the LHC's goals, the role of the Electromagnetic Calorimeter, and the identification of W+jets signals. The conclusion emphasizes the need for further analysis, data collection, and exploration of new physics in the W+jets channel.

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Importance of W+jets Analysis at the LHC

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  1. Outline • Standard Model • Importance of W+jets • Large Hadron Collider • Compact Muon Solenoid • W+jets analysis • Summary/Next Steps Kira Grogg, U. Wisconsin

  2. The Standard Model • Fundamental particles: • Fermions (matter) • Electron, muon, tau, corresponding neutrinos • up, down, charm, strange, top, bottom quarks • Bosons (force carriers) • Photon (EM) • Gluon (Strong) • W, Z (EW) • Higgs? (source of EW symmetry breaking) Kira Grogg, U. Wisconsin

  3. Importance of W+jets as Signal • Measure of Electroweak Interaction at much higher energies • Test of perturbative QCD calculations • Verification of theoretical cross-section and parton distribution functions (PDFs) • High-statistics detector calibration tool Kira Grogg, U. Wisconsin

  4. W+jets as Background • top production (ttbarWbWb) • Higgs production Kira Grogg, U. Wisconsin

  5. W+jets as source of new physics • WW resonance? Kira Grogg, U. Wisconsin

  6. The LHC Goals Goals for the 14 TeV p-p accelerator: • More precise measurements of known particles • Produce and find the Higgs boson • Find evidence of supersymmetry • Explore the energy frontier • New physics Kira Grogg, U. Wisconsin

  7. Electromagnetic Calorimeter • Measures e/ energy within || < 3 using 76,000 lead tungstate (PbWO4) crystals • Will measure energy of electron from W decay • Resolution: Kira Grogg, U. Wisconsin

  8. Electromagnetic Calorimeter • Measures e/ energy within || < 3 using 76,000 lead tungstate (PbWO4) crystals • Will measure energy of electron from W decay • Resolution: • Lead tungstate crystals • Density 8.3 g/cm3 • Molière radius 2.2 cm • Radiation length 0.89 cm • Crystal size: 2.4x2.4 cm x 25.8 X0 Kira Grogg, U. Wisconsin

  9. Software trigger Multi-processor farm Reduces L1 rate to 100 Hz Finds an electron: Energy deposit in ECAL Track reconstruction Match ECAL and track information We rate: ~2 Hz = 106 / yr (L = 1032 cm-2 s-1, 1 yr = 100 pb-1) ET Tracker Strips Pixels pT Electron High Level Trigger Kira Grogg, U. Wisconsin

  10. The Electron and Neutrino • Electron selection: • ET > 15 GeV for an EM cluster, • |cluster| < 1.4 for barrel electrons • 1.6 < |cluster|< 2.4 for endcap electrons • Small energy deposit in HCAL • EHad/EEm < 0.05 • Matched track, within • Isolated: no nearby energy or other tracks • Missing Transverse Energy • Neutrino only ‘detectable’ from missing energy • Expect about 30 GeV of ETmiss • These cuts will be applied to following plots Kira Grogg, U. Wisconsin

  11. CDF W + n jets, Jet ET • Jet transverse energy is reasonably well described by MC samples -- after much tuning of the PDFs LHC will have much higher statistics at this range and beyond Uncertainty is in the background fraction Kira Grogg, U. Wisconsin

  12. Generation of SignalW+jets Kira Grogg, U. Wisconsin

  13. Signal Identification Kira Grogg, U. Wisconsin

  14. ET of top three jets for 3-jet events Jet ET > 15 GeV Elec pT > 15 GeV cut Kira Grogg, U. Wisconsin

  15. Signal Identification Kira Grogg, U. Wisconsin

  16. Conclusions/Next Steps • Conclusions • W+jets is a good signal to look for soon after LHC startup • High cross section • Expect about ~107 events in the first year with L = 100 pb-1 • LHC will be able to explore new energy regime and gluon processes. • Next Steps • Commission trigger system • Simulate backgrounds to W+jets • Take data • Use signal to tune MC simulations • Look for new physics in W+jets channel • Need to understand as background to new physics Kira Grogg, U. Wisconsin

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