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hw04 - ¯ b The main background is Wb ¯ b production where...

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PHZ 6358: Standard Model I Fall Term 2011 Homework Set 4 Due Wednesday, September 28, 2011 Problem 1. Higgs production at the Tevatron. The main production process used for a discovery of a light ( m h < 140 GeV) Higgs boson at the Tevatron is p ¯ p Wh . In this exercise we shall calculate its cross-section using CalcHEP. (a) Start up CalcHEP and generate the diagrams for p ¯ p W + h and p ¯ p W - h . Without doing any calculations, try to guess and rank the Frst few dominant subprocesses according to their importance. (b) Calculate the cross-section for p ¯ p W ± h at the Tevatron ( E CM = 2 TeV) as a function of the Higgs mass m h , for 100 < m h < 200 GeV. Hint: The cross-section is a slowly varying function of m h , so you will only need to compute it at 3-4 points. (c) Check your guesses from (a) against the numerical results from (b). Problem 2. Higgs production at the Tevatron: signal versus background. ±or a Higgs discovery in p ¯ p Wh at the Tevatron, one makes use of the decays W ℓν and h b ¯ b . The Fnal state signature is therefore ℓνb
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Unformatted text preview: ¯ b . The main background is Wb ¯ b production, where the b ’s were produced through a gluon, photon or a Z . On the same plot, show the b ¯ b invariant mass distribution M b ¯ b for the Wh signal and the Wb ¯ b background. Notice that because of the very small Higgs width Γ h , the signal will peak very sharply at M b ¯ b = m h . In reality, however, the energy of the b-jets is not perfectly measured, which results in an uncertainty in M b ¯ b of order 10%. An easy way to account for the poor mass resolution and thus make our plot more “realistic”, is to simply in²ate the Higgs width Γ h to 0 . 1 m h ∼ 12 GeV. Hint: You may need to use the option “regularization” to constrain M b ¯ b near the s-channel gluon, photon, Z or H resonances. Problem 3. Higgs production at the LHC. Repeat Exercise 1, but for the case of Higgs production in vector-boson fusion at the LHC ( pp collider, E CM = 7 TeV). 1...
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