Unformatted text preview: 253a/Schwartz Due November 23, 2010 Problem Set 11 The Higgs is a (hypothetical) real scalar particle which couples to the standard model as L higgs =- 1 2 φ ( square + m h 2 ) φ + λ i φψ ¯ i ψ i + ψ ¯ i ( i∂- m i + g z Z ) ψ i + 1 2 Z μ ( square + m Z 2 ) Z μ + λ Z φZ μ 2 + (1) λ i is called a Yukawa Coupling and is different for each fermion species i . In the standard model, λ i = m i v , where v is the Higgs vacuum-expectation-value, related to the masses of the electroweak gauge bosons: v = 2 m W g w e a k = 246 GeV. Z μ is the Z-boson with m Z = 91 GeV, λ Z = m Z 2 v , and g z ∼ 0.1. 1. Direct Higgs searches. Before the LHC, CERN ran an e + e- collider called LEP, running first (LEP 1) at s √ = 92 GeV then (LEP 2) at s √ ∼ 200 GeV, with ∼ 1 fb- 1 = 10- 39 cm- 2 integrated luminosity for each run. a) What is the partial width Γ (decay rate) for the Higgs to decay to fermion i ?...
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- Particle Physics, Higgs, Elementary particle