Periodic Reporting for period 1 - RAD TORCH (Rare decays of heavy mesons to resonant channels)
Période du rapport: 2023-11-01 au 2025-10-31
Measurements of rare decays of kaons, pions and heavy mesons have become powerful tools to search for new physics beyond the Standard Model. To fully exploit these measurements, experiments such as LHCb require precise theoretical predictions of the underlying strong-interaction effects. These can only be computed using large-scale numerical simulations of Quantum Chromodynamics (QCD) on a space–time lattice.
The objective of this project was to develop and apply advanced lattice-QCD methods to study processes that involve unstable, strongly interacting particles in the final state. The project focused on the resonant form factors that determine rare decays such as B→K*ℓ+ℓ−. These quantities are key inputs for interpreting experimental searches for new physics in the flavour sector. By improving both the methodology and the computational tools, the project aimed to contribute to the long-term precision programme of flavour physics in Europe.
The objective of this project was to develop and apply advanced lattice-QCD methods to study processes that involve unstable, strongly interacting particles in the final state. The project focused on the resonant form factors that determine rare decays such as B→K*ℓ+ℓ−. These quantities are key inputs for interpreting experimental searches for new physics in the flavour sector. By improving both the methodology and the computational tools, the project aimed to contribute to the long-term precision programme of flavour physics in Europe.
The project delivered several major scientific results. First, the physical-point scattering amplitudes describing the ρ and K* resonances were computed and published, providing the first lattice results that controlled all systematic sources of error for these important benchmark systems. The full dataset used in these studies was publicly released through the CERN Document Server.
Second, new software components were developed within a free, open-source software framework, with improvements along all steps of the workflow and optimized performance on modern GPU systems. These tools are now used by several lattice collaborations.
Third, exploratory three-point functions relevant for the rare decay B→K* ℓ+ℓ− were produced on a first ensemble, demonstrating the feasibility of computing these multi-hadron weak decays with fully relativistic quark actions.
Finally, the project contributed to new research directions, including a first lattice investigation of long-distance effects in D-meson mixing.
Second, new software components were developed within a free, open-source software framework, with improvements along all steps of the workflow and optimized performance on modern GPU systems. These tools are now used by several lattice collaborations.
Third, exploratory three-point functions relevant for the rare decay B→K* ℓ+ℓ− were produced on a first ensemble, demonstrating the feasibility of computing these multi-hadron weak decays with fully relativistic quark actions.
Finally, the project contributed to new research directions, including a first lattice investigation of long-distance effects in D-meson mixing.
The project’s results advance the state of the art in multiple ways. The published physical-mass ππ and Kπ scattering studies represent a major step forward in precision studies of light resonances. Making the full dataset openly available sets a new standard for reproducibility in lattice QCD.
Methodologically, the improved computational tools and GPU-accelerated kernels reduce the cost of multi-hadron studies and enable calculations that were previously impractical. The exploratory work on B→K* ℓ+ℓ− is the first step towards a full treatment of rare heavy-meson decays with resonant final states, a problem of high relevance for current and future flavour experiments.
Together, these advances strengthen the theoretical foundations required for interpreting precision measurements at LHCb, Belle II and future European facilities.
Methodologically, the improved computational tools and GPU-accelerated kernels reduce the cost of multi-hadron studies and enable calculations that were previously impractical. The exploratory work on B→K* ℓ+ℓ− is the first step towards a full treatment of rare heavy-meson decays with resonant final states, a problem of high relevance for current and future flavour experiments.
Together, these advances strengthen the theoretical foundations required for interpreting precision measurements at LHCb, Belle II and future European facilities.