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In high energy physics there are different channels of particle production: t-channel, s-channel. What do they mean? And are there any other channels besides "t" and "s"?

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These are basically ways of describing which leading diagram contributes the largest term to the cross-section; they are named after which of the Mandelstam variables characterizes the 4-momentum of the virtual particle.

In t- and u-channel processes the 4-momentum of the exchange particle is space-like (has a negative norm).

In the s-channel the 4-momentum of the exchange particle is time-like (has a positive norm). This necessitates the annihilation of the incident particles.

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Thank you. Now it's more clear to me. –  BartoNaz Oct 17 '12 at 13:21

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