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Calibration of High Pt Hadronic W

Calibration of High Pt Hadronic W. Outline Introduction High Pt Hadronic W in TTbar and Higgs events Reconstruction Algorithm MC based calibration of W Pt Correlation between W Pt cut and W mass scale. Haifeng Pi 10/16/2007. Origin of the Topic.

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Calibration of High Pt Hadronic W

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  1. Calibration of High Pt Hadronic W • Outline • Introduction • High Pt Hadronic W in TTbar and Higgs events • Reconstruction Algorithm • MC based calibration of W Pt • Correlation between W Pt cut and W mass scale Haifeng Pi 10/16/2007

  2. Origin of the Topic Di-jet resonance from W is a critical component in a number of important physics studies TTbar analysis (Tt  b+ W (lv) + b + W (jj)) Wt (Wt  lv + b + W(jj)) Vector Boson Fusion Higgs (qqH(H WW)  qq + lv + jj) V-V scattering (qqWW  qq + lv + jj) Existing Issues: The tuning jet reconstruction algorithm for hadronic W events was missing for a long time at LHC. The reconstruction for the high mass Higgs with hadonic W is largely based on the jet algorithm for single and “isolated” jets with its calibration constant. The strong dependency between properties of reconstructed di-jet system and the selection cuts which are supposed to cover a wide Higgs mass range needs to be understood. (The selection cuts is mass-dependent) What this analysis about: tuning of algorithm for the di-jet system, data driven strategy, basic performance …

  3. Signal events In the final states from qqH,HWWlvjj (we only consider e/), the number of signal events in 30 fb-1 based on Leading-Order Generated Higgs Mass-Distribution (mH =700 GeV, =74.5 GeV) The cross section we used is consistent with previous CMS Note(s) and recent reports from other channels (qqH, HZZlljj) within ±5%. ATLAS cross sections is consistent with CMS in the low-mediate mass range, but 10-20% higher for MH > 700 GeV/c2. So CMS results might be more conservative in high mass.

  4. Hadronic W mass in Higgs and TTbar After applying lepton trigger and isolation, and basic selection cuts (at least 4 jet with ET > 25 GeV, and MET > 30 GeV) Higgs, mH=700 GeV TTbar W+4jets

  5. Higgs mass distribution after selection (MH=600 GeV/c2) Large signal to background ratio, visible mass peak and shape, right mass scale

  6. Mass-dependent W pt cut MH=300 GeV/c2 MH=700 GeV/c2 MH=400 GeV/c2 MH=900 GeV/c2 MH=500 GeV/c2 The W mass cut, Forward jet tagging cut are slightly different to maximize the discovery potential . Details are summarized in Appendix.

  7. Fitting of S and B in lower mass range (MH = 300 GeV) Background -- Convoluted Landau and Gaussian distribution Signal – Gaussian distibution

  8. Discovery potential vs MH at 30 fb-1 • Best discovery potential near 600 GeV • High mass range is limited by statistics (although a higher S/B can be achieved) • Low mass range is limited by large W+jets background

  9. Background Samples Full matrix element event generator + FAMOS Pythia + Full simulation TTbar+ jets 3.5 million W/Z + jets 4.5 million Pythia + FAMOS QCD 400 million

  10. Hadronic W Properties Di-quark W

  11. Jet Pt in Different Samples Various distributions show strong similarity between TTbar and H300

  12. Matching Quark to Jet Di-jet Eff vs  Di-jet Eff vs Pt Matching R < 0.3

  13. Hadronic W Reconstruction Di-jet re-clustering algorithm: Step 1 using standard iterative cone (IC) jet algorithm with 0.5 cone size to get the “jet-seed” Step 2 applying gamma-jet calibration Step 3 applying jet Et threshold 25 GeV Step 4 using jet-seed of closest two jets in space to reconstruction the di-jet cluster Step 5 using E-scheme to calculate the di-jet cluster Step 6dedicated W pt scale and improvement of energy resolution The data-driven analysis using TTbar events for the hadronic W mass reconstruction is under separate study Another di-jet approach has been investigated by colleagues at Fermilab (CMS IN 2006/004). The comparison is also under way.

  14. Mass of Di-jet System New di-jet clustering Algorithm Using standard di-jet for the mass reconstruction

  15. di-quark (di-jet) R Interested region of merged di-jets: R < 1.5 The refined analysis will adapt the R cut with the W Pt cut or targeted Higgs mass. Di-quark Di-jets

  16. MC-based W Pt Calibration

  17. Calibration vs W Pt Cut >50 >70 Pt > 30 GeV/c >90 >110 >130 >150

  18. Dependencies on W Pt Cut W Mass Resolution W Mass Nominal S/B

  19. Summary • New di-jet clustering algorithm is developed to reconstruct hardonic W with better performance in mass resolution and offline selection efficiency • MC-based W Pt calibration based on di-jet cluster is studied. The corrected W Pt help restore the MET scale and resolution • Data driven calibration using TTbar events is studied based on one isolated lepton + 4 jets signature. The S/B is big enough to perform the calibration • The similarity between TTbar and Higgs events reduces the systematic uncertainties of applying the calibration constant to Higgs analysis • W+jets is the most important background channel. But the combinatory background of TTbar events is more serious in the high Pt region • The calibration can be achieved with 1-2 fb-1 of data for early discovery or exclusion. High precision can be achieved in 8-10 fb-1. The time scale fit well into the Higgs discovery or exclusion of VBF Higgs and V-V scattering …

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