Introduction to QCD slides - P.Hoyer.pdf - High Energy Physics Group
Introduction to QCD slides - P.Hoyer.pdf - High Energy Physics Group
Introduction to QCD slides - P.Hoyer.pdf - High Energy Physics Group
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No exclusive amplitudes for charged particles (I)<br />
The identification of the data on e + e – → 2 jets with the <strong>QCD</strong> process<br />
e + e − → q¯q<br />
Gauge invariance dictates that amplitudes<br />
with external charged particles vanish:<br />
Paul <strong>Hoyer</strong> Mugla 2010<br />
requires care, since the latter does not exist!<br />
This is a general feature of gauge theories, and as such is best illustrated by<br />
the QED process e + e − → µ + µ −<br />
A(e + e − → µ + µ − ) = 0<br />
This is because the amplitude must be invariant under local U(1) gauge<br />
transformations. Multiplying one of the external fermions by<br />
U = e iπ = – 1 we get A → – A.<br />
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