The Standard Model (SM) of particle physics describes most fundamental phenomena in particle physics extraordinarily well, but unresolved questions remain. There is for example more matter than antimatter in the universe, but we don’t know yet where this asymmetry originates from. New Physics, able to resolve these questions, can show up in proton-proton collisions at a particle accelerator as new particles or new interactions.
Until today no such New Physics has been found in direct searches. So it must be either extremely rare or manifest at higher energies that can only be probed by precision measurements which are compared to the predictions of the Standard Model. If a significant discrepancy between prediction and measurement is observed, it would indicate New Physics.
One of the most precise predictions of the SM is lepton flavor universality, stating that the three charged leptons (electrons, muons and taus) have equal strength of interaction with other particles. In the past years however, discrepancies from lepton flavor universality have emerged in decays of particles including b quarks (“B hadrons”).
However the current experimental precision is not sufficient for a discovery due to the limited size of data sets. Therefore, the LHCb experiment at CERN is being upgraded to measure B hadrons at higher rates. But at these rates, efficient selection of signals requires exceptional computing demands. From 2022 to 2024, LHCb has commissioned a real-time analysis system based on graphics processing units (GPUs) that can analyze the 30 million proton-proton collisions per second to keep only the most interesting 1 million collisions per second.
With the ALPaCA project, we will exploit the computing resources available thanks to the GPU system to increase the efficiency for selecting B hadron decays. This will allow for more precise measurements of lepton flavor universality. In particular, we aim at the first measurement of electron-tau universality with semileptonic decays at LHCb. This measurement will contribute to the puzzle of anomalies observed in B hadron decays.