Strong Coupling Constant αs Determined to Five Parts Per Mille Using Low-Energy Input

Improved Precision for Strong Coupling

The strong coupling constant, αs, which describes the interaction between quarks and gluons, has been determined with significantly improved precision. A new calculation, published in Nature, has reduced its uncertainty to five parts per mille. This marks a substantial improvement over previous measurements, which were known only to one part in a hundred.

Addressing a Theoretical Bottleneck

This enhanced precision is crucial for high-energy physics. Experiments at the Large Hadron Collider (LHC) measure many process rates to the percent level. The previous uncertainty in αs had become a theoretical bottleneck, limiting the accuracy of predictions. Future facilities, such as the High-Luminosity LHC and proposed Higgs factories like the FCC-ee, will require even greater precision to detect small discrepancies that could indicate new physics.

Independent of Collider Data

A key aspect of this new determination is that it relies solely on low-energy input. This means the value of αs can be incorporated into collider predictions without being fitted to collider data itself, providing an independent and robust measurement. This method avoids potential biases that could arise from using the same data for both measurement and prediction.

Role in Quantum Chromodynamics

The strong coupling αs is a fundamental parameter in Quantum Chromodynamics (QCD), the part of the Standard Model that describes the strong force. It dictates the strength of interactions between quarks and gluons. For instance, the probability of gluon fusion, a process that produces Higgs bosons at the LHC, is proportional to αs². A precise value of αs is therefore essential for understanding and predicting processes involving these fundamental particles.