Trigger Hodoscope

    The Trigger Hodoscope consists of parts of scintillation counters used in the L3-cosmic experiment at CERN until 2000. It was installed in Zeuthen by the DESY L3-cosmic group to perform systematic studies with cosmic particles for possible future projects. Since 2010 the hodoscope has been continuously taking data which is available via the web portal Cosmic@Web to offer students the possibility to investigate cosmic particles.


      The Trigger Hodoscope consists of:
      • 3 scintillation detector planes with 4 independent segments per plane.
      • every segment is read out by 2 PMTs to avoid random signals.
      • a DAQ card,
      • electronics modules for the high voltage supply of the PMTs and for data acquisition.
      • a notebook to control settings in the electronics and to store the data.

      The schematic illustration shows the 3 detector planes. The distance between 1 (top) and 2 is 70cm, between 2 and 3 (bottom) 220cm. One segment has an area of 0.5 × 0.5 m2 and consists of 4 scintillator tiles. If a cosmic particle traverses the scintillator, it creates a short scintillating light flash which is directed to the two PMTs via the light guiding fibres (embedded in the scintillator plates). The signal will only be accepted as an event, if both PMTs detect the light simultaneously.

      Additional coincidence conditions require a signal to appear in at least one segment of each plane. If each plane shows exactly one signal, there is a high probability that a muon was detected. Another coincidence setting enables further interpretation: if all three planes show signals in all four segments, the event is considered a particle shower. But to simplify the analysis, only one additional coincidence requirement is used: every plane has to show a signal in all four segments, which is the indicator of a particle shower.

      Data Structure

        Cosmic@Web provides the following data per hour for the Trigger Hodoscope since 2010: time, number of triggers per hour (from muon candidates) for the different geometrical combinations, total number of muon candidates per hour, number of particle showers per hour, atmospheric pressure, temperature, humidity. More details can be found in the description of the dataset.

        Possible Student Exercises

        • Estimate the frequency of muons for all 16 possible coincidence (trigger) conditions, for the total number of muons as well as the number of showers in dependence on time.
        • Analyse the dependency of the muon rate on atmospheric pressure, temperature and humidity.
        • Compare the results of different years.
        • Compare the rates with your independent data collection from the CosMO or Kamiokannen detectors.
        • Search for extreme solar events which produce so-called Ground Level Enhancements (GLEs) and lead to an increased cosmic particle rate within a few hours.
        • Search for Forbush Decreases caused by strong solar winds, that reduce the rate of cosmic particles.
        The last two proposals require an air pressure correction of the particle rates. References to GLEs and Forbush events can be found in the internet.

          Example Diagrams

            At Cosmic@Web you will find few example diagrams using the Session-ID Trigger-Hodoskop.

            Muon Rate-Time-Diagram