Quarks on the mark

The most precise measurements to date of the strength of the couplings between different fundamental particles known as quarks are reported online in Nature Physics this week. The measurements provide a fundamental input parameter for the standard model of particle physics and represent a stringent test of its accuracy.

In the standard model of particle physics, which describes the properties and interactions of fundamental particles, the decay of one quark to another is described by the so-called Cabibbo-Kobayashi-Maskawa (CKM) matrix. For the standard model to hold, the input parameters for the CKM matrix from different fundamental processes must be consistent with each other. By taking advantage of recent technical improvements at CERN’s Large Hadron Collider, the LHCb collaboration reports the first measurement of CKM matrix elements based on decays of baryons, particles made of three quarks.

The results of this approach are complementary to those of previously reported methods based on decays of mesons, which are particles composed of two quarks. These measurements are expected to have a significant impact on the quantitative understanding of the fitting parameters to the CKM matrix and allow constraints to be placed on any possible extensions of the standard model.