Theorists in the HPQCD collaboration have pinned down Vcs, a key parameter of the Standard Model, using STFC’s DiRAC Data Intensive supercomputer at Cambridge.
Vcs is determined from combining the theoretical calculation with results from particle physics experiments around the world for the proportion of D mesons that decay to a K meson in a process akin to nuclear beta decay.
This rate depends on the coupling strength Vcs between the W boson of the weak interaction and the charm-strange quark pair, but also on the strong interaction physics, encoded by ‘form factors’, that binds the quarks inside the mesons while this process happens.
The numerical techniques of lattice QCD allow the form factors to be calculated, but in the past their uncertainty has limited the precision of Vcs.
Using improved methods for handling quarks, developed by HPQCD, physicists in Cambridge and Glasgow have now obtained a value for Vcs of 0.9663(80), three times more accurate than previous work. This allows Vcs to be distinguished from 1 for the first time, giving tighter constraints on the possibilities for new physics beyond the Standard Model.
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