The data acquisition for the BGO-OD experiment

Abstract

The BGO-OD experiment at ELSA was constructed to study meson-photoproduction.A main focus of the experiment is on associated strangeness and vector meson production.As these reactions are dominated by t-channel contributions their cross sections peak in forward direction.This motivates the two part detector design.While most of the angular range is covered by an electromagnetic calorimeter, the forward region is equipped with an open dipole spectrometer.This combination makes BGO-OD an unique setup.As the cross sections for interesting reaction channels are low compared to other hadronic reactions, the experiment was designed to operate at the highest possible rates.<br /> For efficient operation this requires a sophisticated data acquisition system.This system was developed within this thesis.While the basic structure of the DAQ could be adapted from the Crystal Barrel experiment, significant modifications and extensions were necessary.To allow for an efficient data acquisition, the readout is distributed across several readout crates.A synchronization system is used to distribute the global trigger signal to all crates.A busy logic is used to ensure no new triggers are accepted until all crates are ready for the next event.To minimize the resulting dead time most of the readout is performed after the busy is reset.This allows to achieve dead times of approximately 50 μs.After readout the data is sent to a central event saver which assembles the data from all crates and saves them to disk.A dedicated control program manages the interactions between the readout and saver programs as well as the user interface.<br /> With this setup the first data was taken in 2014.The data acquisition system operated at an event rate of approximately 850 Hz with a life time above 90%.The data from the various detector components was investigated and found to agree with the expectations.On this basis hadronic reactions were reconstructed.The reactions γp to pπ⁰ and γp to pη could be observed using only the BGO electromagnetic calorimeter.The reaction γp to ΛK⁺ is more difficult to observe due to its significantly lower cross section.However, using combined data from all detector components, a kaon signal can be easily identified.<br /> The BGO-OD experiment is now pursuing its physics program.The DAQ system introduced in this thesis allows this to be done efficiently while providing the flexibility to adapt to future developments.