Optical fiber center module for the KOTO experiment

We introduce a new Optical Fiber Center Module for the Trigger Upgrade in the KOTO Experiment at J-PARC, Japan. The KOTO DAQ consists of nearly 4000 ADC channels over 18 crates. Running in parallel with the Total Energy based L-1 Trigger, the Cluster Trigger uses cluster bits from all 2716 channels in the CsI detector. For each ADC channel, a number of successive samples are analyzed upon a L-1 Trigger, and a bit is set High when the peak sample is above a defined threshold. These values are calculated inside the 176 CsI-ADC modules, and collected for each crate into a Clock Distribution and Trigger Module. In the first KOTO Cluster Trigger Implementation, a 3-layer Clock Distribution and Trigger Module pyramid scheme was employed to bring all cluster bits in one place. This new Optical Fiber Center is a 6UVME module with 18 SFP transceivers and one Intel Arria 5 FPGA. It can communicate directly with all 18 Clock Distribution and Trigger Modules and generate a cluster map for the entire detector with minimal dead time and latency. Cluster numbers are then calculated and sent to the Trigger Master. They are used in combination with Et, for an enhanced L-1 Trigger decision.