Test of lepton flavor universality and real time event selection on GPUs at LHCb

par Dr Dorothea Vom Bruch

jeudi 27 févr. 2020, 11:00 → 12:00 Europe/Paris

Grand amphithéâtre (LPSC)

In recent years, tensions between measurements and Standard Model predictions in the decays of b-hadrons, have hinted at the possible violation of lepton universality, specifically in observables in b→sll and b→clυ transitions. Among them is the ratio of branching fractions R(D*)τμ = B→ D*τυ/ B→ D*μυ. I will discuss the first measurement of the the ratio R(D*)eμ = B→ D*eυ / B→ D*μυ at the LHCb experiment at CERN, which which will lead to a combined measurement of all three lepton species. The LHCb experiment is currently being upgraded for Run 3 of the LHC to record more statistics and therefore reduce the uncertainties of observables testing lepton flavor universality. After this upgrade, LHCb will run without a hardware level trigger in 2021, resulting in the complete detector being read out at the full bunch-crossing rate of 30 MHz and a maximum data rate of 40 Tbit/s. Events of interest are selected with a software-only trigger in two stages. This allows unprecedented flexibility for trigger selections but at the same time poses a significant computing challenge. In this seminar, I will also present the ``Allen'' project, capable of processing the full first trigger stage, High Level Trigger 1 (HLT1), on about 500 state of the art graphics processing units (GPUs). During HLT1, a sub-set of the full offline track reconstruction for charged particles is run to select particles of interest based on single or two-track selections. Allen enables the exploitation of LHCb's broad physics program in Run 3. As the first complete high-rate GPU trigger, it has the potential to significantly impact the trigger systems of other HL-LHC experiments, as well as experiments at future facilities and colliders.