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How can the strong coupling constant be measured?

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I’ll try to explain one method that measures ${{\alpha }_{s}}$ within ±8% at very high energies. Consider $pp$ or $p\bar{p}$ collisions with CM energy in the TeV range. What happens in the events of interest is that one “parton” from each of the nucleons participates in hard scattering via single-gluon exchange, and the rest of each nucleon proceeds essentially undisturbed, with a substantial fraction of the nucleon’s initial momentum and <1 GeV/c of deflection. You should see four distinct jets, two of them along the axis of collision and two at large angles. The experimental technique involves measuring the 4-momentum of each jet. The 4-momentum of each deflected parton can be inferred from the different between the momentum of the incoming nucleon and that of the undeflected jet. The 4-momentum of the gluon can in turn be inferred from the difference between the momentum of the deflected parton and that of the outgoing jet. Since the differential scattering cross-sections for $qq$ and $q\bar{q}$ are well known, aside from the coefficient, the measured statistics reveal ${{\alpha }_{s}}(t)$. (Minor complication: In $qq\to qq$ scattering, there is a u-channel process that interferes with the t-channel process.)

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Through literally hundreds of experiments of dozens of process types, involving the strong interactions, and coordinated comparisons of precision measurements with detailed calculations of Quantum Chromodynamics (QCD).

In the last 40 years, dozens of ingenious handles for precision determinations have been devised and compared, cf

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