NOvA Data Acquisition System

Abstract

Abstract The NOνA (NuMI Off-Axis νe Appearance) experiment is a long-baseline neutrino experiment using the NuMI main injector neutrino beam at Fermilab and is designed to search for νμ (oνμ) to νe (oνe) oscillations. The experiment will consist of two detectors; both positioned 14 mrad off the beam axis: a 220 ton Near Detector to be located in an underground cavern at Fermilab and a 14 kton Far Detector to be located in Ash River, MN, 810 km from the beam source. In addition, a prototype Near Detector is currently in operation in a surface building at Fermilab. The detectors have similar design, and consist of planes of PVC extrusion cells containing liquid scintillator and wavelength shifting fibers. The fiber ends are readout by Avalanche Photodiodes (APDs). The primary task for the Data Acquisition (DAQ) system is to concentrate the data from the large number of APD channels (360000 channels at the Far Detector, 16000 channels at the Near Detector), buffer this data long enough to apply an online trigger, and record the selected data. The concentration of data is accomplished through the use of a custom hardware component Data Concentrator Module (DCM). The intermediate buffering of the data is accomplished through a computing buffer farm, in which each node runs software to apply an online trigger to a time slice of data received from the DCMs. Data correlated with the beam spill time as well as random data samples for calibration purposes and events with interesting topology may be selected by the online trigger. In addition to those components involved in managing the data flow, the DAQ system consists of components for control, configuration, monitoring and timing. The design of the DAQ system, with emphasis on the DAQ software, will be discussed as will experience with its deployment on the prototype Near Detector.