Physics quiz question: Feynman diagram interpretation

Physics 205B Quiz 7, spring semester 2017
Cuesta College, San Luis Obispo, CA

This Feynman diagram depicts a(n) __________ process.
(A) β^–.
(B) β⁺.
(C) electron capture.
(D) (This process is not possible, as it is invalid.)

Correct answer (highlight to unhide): (D)

This Feynman diagram vertex is invalid, because it violates charge conservation. Tracing the proton line left-to-right shows that it converts into a neutron, and so the outgoing intermediate vector boson must be positively charged (W⁺) to conserve charge for that vertex. However, at the bottom vertex it is not possible for the neutrally charged neutrino (ν) to absorb that positively charged intermediate vector boson in order to convert to a negatively charged electron.

Sections 30882, 30883
Exam code: quiz07N4ci
(A) : 9 students
(B) : 12 students
(C) : 6 students
(D) : 0 students

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