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1. Study of Hadronic W Decays in the Jets + MET Final State KittikulKovitanggoon and Dr. Sung-Won Lee (Advisor)Department of Physics, Texas Tech University Large Hadron Collider (LHC) Peak position Peak position CMS 300-500 GeV/c2 Ebeam= 7 TeV p p LHCb Log Scale ATLAS Normalization Region ALICE Methods • 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 seem to work on SUSY signal. • However, this analysis is still in the early state. More detail studies are required • 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. 1 Entries Entries • 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 final state, we will face a large combinatorial background in dijet mass, the previous methods of extracting hadronic W decay in Jet+MET final state cannot give the mass 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 final state. This method will use the 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. MW MW Entries Entries Entries Entries • Top Pair Production • The b-tagger of High Efficiency Track Counting is used in this analysis. • Calorimeter Jets Entries Entries MW Same Events Mixed Events • 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. Entries Entries Entries Entries • References: • Y. Pakhotin et al., “SUSY survey with inclusive muon and same-Sign dimuon accompanied by jets and MET with CMS” , ActaPhys.Pol.B 38,2(2007)653-660 • C. Amsler et al., “Review of Particle Physics”, Physics Letter B 667, 1(2008) • A. Nikitenko, E. Yazgan, “Jet Energy Scale Evaluation for Tagging Jets in Vector Boson Fusion Higgs Production”, CMS-AN-2010/004 • 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) Entries Entries Peak position MW MW MW