New online system without hardware trigger for the Super-Kamiokande experiment

A new online system of the underground neutrino detector, Super-Kamiokande is scheduled to be introduced in 2008 together with front-end electronics. This detector is equipped with about 13000 photo-multipliers (PMTs) to detect Cherenkov light generated in the water. In the new data acquisition scheme, we will not use a hardware event-trigger but read out every hit data from the front-end electronics and process them by the online farm. Therefore, there is no threshold of the number of PMT hits and the detector will become more sensitive to important cosmic-ray events such as relic neutrino from supernova and low energy solar neutrino. The test of the prototype online system together with new electronics has been done using the part of Super-Kamiokande detector. In this paper, the design of the upgraded online system and the results of those testing activities will be described.