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M W Entri es Entri es Peak position M W Same Events Mixed Events Study of Hadronic W Decays in the Jets + MET Study of Hadronic W Decays in the Jets + MET Final State Final State Kittikul Kovitanggoon and Dr. Sung-Won Lee (Advisor) Department of Physics, Texas Tech University Abstract Top quarks are dominantly produced in pairs and they will be abundantly created at LHC. Top quark decays almost exclusively to a W boson and a b quark, therefore the detection of W bosons is vital. W can decay hadronically ( W jj ) for 70% and leptonically ( W lν) for 30%. Due to the higher probability of W boson to go though hadronic decay, this will be the channel for us to probe both Standard Model and beyond Standard Model. Because, in all hadronic nal state, we will face a large combinatorial fi background in dijet mass, the previous methods of extracting hadronic W decay in Jet+MET nal state cannot give the mass fi peak at the result of mass (80 GeV). In this study, we present the data-driven method to extract hadronic W decay from this type of nal state. This method will use the fi uncorrelated jets to imitate combinatorial background and eliminate this background from the signal. This method is tested on Monte Carlo simulation of the Standard Model Top pair productions and Super Symmetry Low Mass point 7 (SUSY LM7). Also, the preliminarily search for hadronic W decay in collisions at = 7 TeV at LHC is shown. Top Pair Production • The b-tagger of High Efficiency Track Counting is used in this analysis. A.Calorimeter Jets Methods Conclusion • Extracting the hadronic W decay is important for both Standard Model and SUSY events. • The studies show that the data-driven method seems to work on extracting hadronic W. • Proper b-tagging could help us to see clearly mass peak with less combinatorial background. • Various jet energy corrections and PF jets can solve the over-calibrating energy. References: 1.Y. Pakhotin et al., “SUSY survey with inclusive muon and same-Sign dimuon accompanied by jets and MET with CMS” , Acta Phys.Pol.B 38,2(2007)653-660 2.C. Amsler et al., “Review of Particle Physics”, Physics Letter B 667, 1(2008) 3.A. Nikitenko, E. Yazgan, “Jet Energy Scale Evaluation for Tagging Jets in Vector Boson Fusion Higgs Production”, CMS-AN-2010/004 4.U. De Sanctis, T. Lari, C. Troncon, “Perspectives for the detection and measurement of Super-symmetry in the focus point region of mSUGRA models with the ATLAS detector at LHC”, Eur.Phys.J.C52:743-758(2007) t t p p s CMS ALICE ATLAS LHCb E beam = 7 TeV p p Large Hadron Collider (LHC) 1 • The different jet energy corrections is applied to correct the over-calibration of jet energy. • In comparison of the three jet energy corrections, quark-jet energy correction gave us the better W boson mass. However, we lost some jets due to the lower jet energy in this correction. With this results, we can clearly see that the data driven seem to eliminate the high tail mass background well. B. Particle Flow Jets • With track information, the over calibrated jet energy is not an issue. • Combined with high efficiency b-tagger, the clear peak at 80 GeV of W mass is evident. SUSY LM7 Production • Supersymmetry (SUSY) provides an elegant solution for a cold dark matter candidate. The minimal SUGRA framework indicate that gluinos is lightest. The gluinos decay to pairs of tops plus the lightest supersymmetric particle (LSP). • This results show that data-driven method Entri es Entri es Log Scale Normalizati on Region 300-500 GeV/c 2 Entri es Entri es Entri es Entri es Peak position Peak position Entri es Entri es M W M W t t ) )( )( ( 0 1 0 2 ~ b W b W ~ t t g ~ Entri es Entri es M W M W Test on Early LHC Data at = 7 TeV Modified Data-Driven Method Result •The peak position lower than W mass because many QCD jets passed our event selections. • This method is still pre-mature. We need more detailed studies. s Entri es Entri es
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