Flavour Physics arms researchers to unlock universe's subatomic secrets

An international review of lattice flavour physics founded by researchers at the University of Southampton is equipping scientists to extend beyond the esteemed Standard Model.

Over 30 scientists from all around the world are gearing up for a fifth edition of the Flavour Lattice Averaging Group (FLAG) report, which analyses numerical simulations of lattice results to frame efforts to quantify strong-interaction effects.

The previous edition has been the most-cited article in the European Physical Journal C (EPJC), with the most recent figures from the FLAG report featuring on the journal's cover earlier this year.

The Southampton High Energy Physics theory group’s Dr Andreas Jüttner and Professor Chris Sachrajda were founding members of FLAG in 2007. The aim was to unite experts in Lattice Field Theory, Chiral Perturbation Theory and Standard Model phenomenology from all around the world and to provide a service to the wider community.

In flavour physics, elementary particles known as quarks are understood to come in different 'flavours', a property similar to their mass, charge and spin. The particles form part of the Standard Model, a theory that to date remains incredibly successful in correctly describing and predicting properties and behaviour of elementary particles. However, much of the known universe is not explained by the theory. Any tension between Standard Model predictions and findings in particle physics experiments could therefore point to yet undiscovered new physics.

The FLAG group summarises the main features of new calculations to provide a framework for judging and combining the different results. These sometimes produce a single result to be used as a best value in future experiments, but more often it recommends a combination of results from different collaborations.

"As the Large Hadron Collider at CERN explores a new energy frontier and experiments continue to extend the precision frontier, the importance of flavour physics will grow," Andreas says. "This will be seen both in terms of searches for signatures of new physics through precision measurements and in terms of attempts to construct the theoretical framework behind direct discoveries of new particles.

"Our aim is to provide an answer to frequently posed questions in a way that is readily accessible to those who are not expert in lattice methods. These are generally not easy questions to answer; different collaborations use different lattice actions with a variety of lattice spacings and volumes. Not only are the systematic errors different, but also the methodology used to estimate these uncertainties varies between collaborations."

This year's European Physical Journal FLAG cover plotted a quantity that is related to the strength by which quarks and gluons couple together, one of the central quantities in modern particle physics.

Researchers met in Bern, Switzerland, earlier in the year to start planning the review's fifth edition. The deadline for inclusion of new results is 30 April 2021 and the fifth edition of the review is expected to appear in October 2021.