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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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)
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 …
In the final states from qqH,HWWlvjj (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, HZZlljj) 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.
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
Large signal to background ratio, visible mass peak and shape, right mass scale
The W mass cut, Forward jet tagging cut are slightly different to maximize the discovery potential . Details are summarized in Appendix.
Background -- Convoluted Landau and Gaussian distribution
Signal – Gaussian distibution
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
Various distributions show strong similarity between TTbar and H300
Di-jet Eff vs
Di-jet Eff vs Pt
Matching R < 0.3
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
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.
New di-jet clustering Algorithm
Using standard di-jet for the mass reconstruction
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.
Pt > 30 GeV/c
W Mass Resolution