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Precise Analysis of W-Pair Cross-Section & Branching Ratios at DELPHI: LEP2 Results Alignment

Presenting the final DELPHI results on W physics at LEP2, showcasing efficient selection techniques like Neural Network and IDA for different W+W- decay modes. Detailed systematic error studies and comparisons with the Standard Model prediction validate the results. The analysis covers various aspects, including background modeling, fragmentation, radiative corrections, and detector effects. Understanding W-pair production dynamics and investigating systematic errors provide valuable insights into subatomic particle interactions.

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Precise Analysis of W-Pair Cross-Section & Branching Ratios at DELPHI: LEP2 Results Alignment

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  1. W-pair cross-section and W Branching ratios at DELPHIG. Gomez-Ceballos (M.I.T.) • *** W Physics was one of the main goals at LEP2*** • Close to the final DELPHI results! • Selection: Different multidimensional discriminant techniques used in the selection • W+W- qq’q’’q’’’ = Neural Network (Eff~80%, Bg~15%) • W+W- qq’ l n = IDA (Eff~75%, Bg~10%) • W+W- l n l’n’= Neural Network (Eff~65%, Bg~10%) “CC03” diagrams of W-pair production at LEP2 Distribution of the Neural Network output variable for four-jets events at Ecm = 207 GeV Distribution of final discriminants for the semi-leptonic selection Distribution of the two types of Neural Network used for the selection of fully-leptonic events Measurements of the WW cross-section compared with the Standard Model Results in agreement with the Standard Model prediction! • Detailed study of systematic errors: • Modelling of 4-jet Background from qq • Background cross-sections • Fragmentation modelling • FSI • Radiative corrections • Luminosity determination • Detector effects • MC statistics W- polar angle differential cross-sections from qqen and qqmn channels Ratios between measured and predicted WW cross-sections with the DELPHI data Breakdown of systematic errors on the partial WW cross-sections at Ecm = 200 GeV

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