Speaker
Description
We are searching for the rare decay $K_L\to\pi^0\nu\bar{\nu}$ in the J-PARC KOTO experiment,
The High Level Trigger (HLT) in the DAQ system was developed with GPUs in 2024. The HLT is composed of two types of computers, Computing Nodes and Disk Nodes. Computing Nodes select events and compress waveforms using GPUs. Disk Nodes store the data temporarily, and the data on the Disk node is transferred to the computing cluster on the KEK 70 km far from the J-PARC.
In 2024, the number of Disk Nodes was one, and the performance of writing to disks on the Disk Node made a bottleneck in some special data taking with high rate.
In the data taking in 2025, an additional Disk node was installed to solve this issue. After this addition of the Disk Node, we evaluated the capability of the whole HLT to handle the trigger rate with beam data.
A new GPU algorithm to monitor a hit rate on a detector was implemented in the HLT. Accidental losses resulting from variations in beam intensity during the beam spill can be evaluated by comparing hit rates between two accidental triggers: a random trigger and a beam-intensity biased random trigger. This monitor can be used to make a quick feedback to the accelerator staffs, and it was actually used to select a better beam configuration in our data taking.
We report the capability of the trigger rate and the new monitoring system on the HLT.