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Published byIvan Worrell Modified over 10 years ago
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First measurement of EWK Z+2j production cross section and hadronic activity in rapidity gap in CMS A.Nikitenko (IC) for 7 TeV Analysis Team March, 2013
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Public PAS. Paper is under CWR
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EWK Z + 2 jet production EWK jj = 255 fb, m ll > 50 GeV, p T j > 10 GeV, | j | 120 GeV VBF H-> = 80 fb for m H =125 GeV Bremsstrahlung VBF multiperipheral Large, negative interference between VBF and others two processes
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Backgrounds 1.Dominant: high order s corrections to DY production: “QCD Z+jets” 2. Small: tt~ production 3. Small: diboson production:
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Analysis strategy Signal is very small (S/B ~ 0.1 after optimized selections), therefore Use different methods to extract signal Confirm signal in and ee modes Use different methods of jet reconstruction JPT jets PF jets
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Event selection cut flow table Uncertainty on the dominant background QCD Z+jets due to JES, +13%, -9% is comparable with the signal. The signal must be extracted from the distributions, most sensitive to the presence of the signal
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Signal is extracted by two methods from fit of m jj from fit of BDT output
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m jj fit; mode S +/- stat B +/- stat JPT jets 1.14+/-0.28 0.869+/-0.008 PF jets 1.14+/-0.30 0.897+/-0.008
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9 Signal extraction from fit of BDTD output Variables for BDTD Pre-selections for 1. p T J1 BDTD: 2. p T J2 3. | J1 - J2 | 4. m jj 5. p T Z 6. y* = y Z – (y J1 + y J2 )/2 7. J1 + J2 8. y Z 9. | J1 - Z | 10. | J2 - Z | 11. | J1 - J2 | | j | < 3.6
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BDTD output fit; and ee modes S +/- stat B +/- stat mode JPT jets 0.90+/-0.19 0.905+/-0.006 PF jets 0.85+/-0.18 0.937+/-0.007 ee mode PF jets 1.17+/-0.27 0.957+/-0.010
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measured cross sections agrees with NLO prediction (VBFNLO): 166 fb at m ll > 50 GeV, p T j > 25 GeV, | j | 120 GeV
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Section: Hadronic activity in rapidity gap
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Check theory expectations with data Jet activity in rapidity gap for QCD Z/W+jets: the larger j1j2, the bigger probability to have additional jet in region between j1 and j2 the larger p T of tagging jets, the bigger probability to have additional jet in region between j1 and j2
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vs jj
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Conclusions First measurement of EWK Z+2j process demonstrates the CMS detector and analysis capability to extract a process which is topologically similar to VBF Higgs production and has a cross section comparable to that in the standard model. First analysis of hadronic activity in the rapidity interval between forward and backward jets in Z+jets process shows good agreement with MadGraph predictions
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Difference in kinematics for EWK Z+jets, VBF H and QCD Z+jets
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Expected Feature 1 the larger p T of tagging jets, the bigger probability to have additional jet(s) between them data confirms simulation predictions
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Expected feature 2 The larger rapidity separation between tagging jets, the bigger probability to have additional jet(s). data confirms simulation predictions
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