Real-time triggering with GPUs in the CERN NA62 K decay experiment

This thesis reports a study for a new real-time trigger for the NA62 experiment based on Graphical Processing Units (GPUs). The aim of the NA62 experiment is to measure the branching ratio of the ultra-rare decay K+→π+v anti-v , a process mediated by Flavour- Changing Neutral Currents (FCNC), with a precision of 10%. Since the value predicted by the Standard Model is very precise, the measurement of this quantity represents an excellent way to investigate the existence of New Physics, or in case of agreement with the Standard Model(SM) should improve the current value of the |Vtd| parameter of the CKM matrix. The use of a high-rate kaon beam will result in an event rate of about 15 MHz, so high that it will be impossible to store data on disk without an ecient selection. The experiment therefore devised three trigger levels, allowing to reduce the data rate fed to the readout PC farm down to ~10 kHz. In this thesis I report a study for a fast multi-ring fitting algorithm, fed with the data of the RICH(Ring Imaging Cherenkov) detector to be used in L0 level trigger of the experiment. The necessity of running the algorithm in real-time, with a maximum latency of 1 ms per event, drove the choice of exploiting the parallel computing power of GPUs. I developed an online seedless ring fit algorithm running on GPUs, satisfying the L0 trigger time requirement which achieves resolutions comparable to the ones obtained by the off line reconstruction. Therefore I studied how the use of the algorithm at L0, increase the quality of the data collected respect to the standard trigger of the experiments for a specific case, the Lepton Violation decay K+→π- l+ l+. The measurement of this decays would be the prove of Majorana nature of neutrinos and the existence of New Physics. This work proves that alternative trigger designs are possible for the NA62 experiment, and represents a starting point for the introduction of flexible GPU-based real-time triggers in High Energy Physics

Electromagnetic Radiation

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