AIDA acts as the active stopper for the beam, and produces data for implantation decay events that occur within it. AIDA consists of three layers, but can function with as many as six. Each AIDA layer is double-sided, with each side consisting of 128 silicon strips. The two sides of strips are perpendicular to each other, which forms a 128x128 grid. Due to this high segmentation AIDA can determine the position of implantation decay events with a reasonable degree of accuracy, and it is this high segmentation that allows for the spatial aspect of the AIDA event building, described here.

AIDA Data Format

The AIDA detector system a trigger-less system with an abnormally low threshold. As a result the MBS data stream is unable to output AIDA events in the same way as the other systems. Instead the data for AIDA is stored in a buffer and sent to the MBS periodically.

The data from each strip is send in two words, the first words contains the FEE64 and channel numbers, which are used to determine its position inside AIDA. This first word also contains the energy measured by that strip. The last useful part in the first AIDA data word is the Implantation/Decay identifier. When the data measured by a single strip exceeds a given threshold, this value is set to 1 and the units of the energy are changed to allow for these higher energy values. The second word consists of the timestamp for that strip, but in order to understand how this is analysed we must first understand the how timestamping is formatted in the AIDA MBS.

AIDA Timestamping

AIDA data in the MBS, like the other systems, starts with a white rabbit timestamp, however as the AIDA data is stored before being sent to the MBS data stream, multiple white rabbit timestamps are needed in order to generate accurate coincidences. This is achieved with a periodic "AIDA White Rabbit".

The AIDA White Rabbit is functionally the same as the normal White Rabbit, but is formatted in four words as opposed to five. When strip data comes in to the system, the second word contains a 28bit timestamp for that event. In order to avoid outputting a new White Rabbit timestamp for every strip, the system is designed such that the 28bit strip timestamp is appended to the periodic AIDA White Rabbit timestamp. Using this method the timestamps of strips can be compared within AIDA itself, as well as with the other detector systems.