Precision Measurements of the Standard Model

cosurgi writes:

More precision measurements are planned at LHC (Large Hadron Collider) [1]. Short extract below:

When ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid) discovered the Higgs boson [2] and confirmed the validity of the Brout-Englert-Higgs mechanism, physicists were hungry for more. But the Higgs was a giant tree hiding a meadow full of well-known flowers. No exotic plants were to be found in these high-energy plains. Month after month, the Standard Model has revealed itself to be more solid than ever. Previously when higher energy at LHC was possible scientists were looking for spectacular phenomena that have now mostly been ruled out. The approach now is to carry out precision measurements.

In reality, the Standard Model is built on two quantum theories: the electroweak theory [3], which describes the electromagnetic and the weak forces, and quantum chromodynamics, which describes the strong force. So, here we have the basics. One advantage of the Standard Model is that it is predictive: it predicts all possible interactions between particles with a precise probability (which physicists call the "cross section"). However, it doesn't predict the masses of the fundamental particles: these are among the parameters measured by the experiments. These masses vary greatly e.g. the heaviest top quark, is almost 90 000 times heavier than the up quark, the lightest. In total, there are 19 free parameters which determine the inner workings of the standard model (aside from the parameters relating to neutrinos). Measuring them precisely is crucial to be able to calculate the interaction cross sections and test the consistency of the Standard Model. Although the Standard Model doesn't predict their values, it ties some parameters together. "By [more precisely] measuring all of these parameters independently, we test the relationships predicted by the Standard Model and impose constraints on physics beyond the Standard Model." explains Andrew Pilkington, a physicist with the ATLAS experiment.

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