1. 1 UCSD Meeting Calibration of High Pt Hadronic W Haifeng Pi 10/16/2007 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

2. 2 UCSD Meeting 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. 3 UCSD Meeting 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 (m H =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 M H > 700 GeV/c 2. So CMS results might be more conservative in high mass.

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

5. 5 UCSD Meeting Higgs mass distribution after selection (M H =600 GeV/c 2 ) Large signal to background ratio, visible mass peak and shape, right mass scale

6. 6 UCSD Meeting Mass-dependent W pt cut M H =300 GeV/c 2 M H =400 GeV/c 2 M H =500 GeV/c 2 M H =700 GeV/c 2 M H =900 GeV/c 2 MHMH W Pt Cut 30065 400120 500160 600190 700190 800200 900210 1000210 The W mass cut, Forward jet tagging cut are slightly different to maximize the discovery potential. Details are summarized in Appendix.

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

8. 8 UCSD Meeting Discovery potential vs M H 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. 9 UCSD Meeting 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 WW + 0/1/2 jetsAlpgen20 million WZ + 0/1/2 jetsAlpgen19.4 million ZZ + 0/1/2 jetsAlpgen10.1 million W + 3/4/5 jetsAlpgen22.1 million Z + 3/4/5 jetsAlpgen17.3 million WW(ewk) + 2jetsMadgraph70 k

10. 10 UCSD Meeting Hadronic W Properties Di-quarkW

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

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

13. 13 UCSD Meeting 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 6 dedicated W pt scale and improvement of energy resolution Another di-jet approach has been investigated by colleagues at Fermilab (CMS IN 2006/004). The comparison is also under way. The data-driven analysis using TTbar events for the hadronic W mass reconstruction is under separate study

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

15. 15 UCSD Meeting 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. 16 UCSD Meeting MC-based W Pt Calibration

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

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

19. 19 UCSD Meeting Summary 1.New di-jet clustering algorithm is developed to reconstruct hardonic W with better performance in mass resolution and offline selection efficiency 2.MC-based W Pt calibration based on di-jet cluster is studied. The corrected W Pt help restore the MET scale and resolution 3.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 4.The similarity between TTbar and Higgs events reduces the systematic uncertainties of applying the calibration constant to Higgs analysis 5.W+jets is the most important background channel. But the combinatory background of TTbar events is more serious in the high Pt region 6.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 …