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u-Channel
The u quantity is does not have a clear cut interpretation like the s and t channels
u≡(P∗1−P′∗2)2=(P∗2−P′∗1)2
u≡(P∗1−P′∗2)2
u≡P∗21−2P∗1P′∗2+P′∗22
u≡2m21−2E∗1E′∗2+2→p ∗1→p ′∗2
In the center of mass frame of reference,
E∗≡E∗1=E′∗1=E∗2=E′∗2=E∗1=E∗2
and
|p∗|≡|→p ∗1|=|→p ′∗1|=|→p ∗2|=|→p ′∗2|
and θ1=−θ2 is the angle between →p ∗1 and →p ′∗2
t≡2m∗1−2E∗21−2|p|∗2cos θ
Using the relativistic term for Energy
E2=→p 2+m2
t≡−2p ∗21(1+cos θ)
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