CosMO-muv (Cosmic Muon Observer Muon Velocity Measurement) is an experiment that measures the velocity of cosmic muons. Three CosMO detectors are placed at a total vertical distance of 3m. The distance between the lower and the middle detector is 1m, the distance between the middle and the upper detector is 2m. This set-up mimics the muons pathway through our atmosphere and therefore maximizes the chances of detection. A signal that registers in all three CosMOs, supplies us with the time that the muon took to fly through the allocated distance. This information enables us to calculate the velocity of the muon.


      This Set-up includes:

      • three CosMO detectors
      • a Data Acquisition card (DAQ card),
      • a rack to place the CosMOs directly on top of each other at distances ranging from 1m to 3,5m,
      • a Notebook including the software muonic.

      When a charged elementary particle, e.g. the muon, passes through the CosMO's scintillator material, the particles in the scintillator are forced into an excited state. The scintillator's atoms almost immediately return to their ground state and emit the excess energy as light. This light signal is transmitted and converted into an electrical signal by the MPPC. The electrical signal is read by the DAQ-card. In order to avoid faulty signals, the muons must fulfill a coincidence condition; only a muon that passes through all three CosMOs is registered. The muon must bypass first the top CosMO, then the middle one and finally the bottom one. Muonic calculates the difference in time between the occurring signals in the individual detectors. The set-up allows three simultaneous measurements: one at 1m, a second at 2m and a third at 3m. The visualization of the difference in time depending on the distance between the CosMOs lets us determine the velocity of cosmic muons.

      Data Structure

        The data on the web interface Cosmic@Web includes: time (h), time (of the signal), atmospheric pressure, temperature, flight time at allocated distances and distance between detectors. More detailed information can be found in the description of the dataset.

        Possible Student Exercises

        • Calculate the muon velocity using the given information about the mean flight time and distance,
        • Investigate existing dependencies between muon velocity and atmospheric pressure or temperature,
        • Calculate the average muon energy using your knowledge of their average velocity,
        • Compare the muon velocity with that reached by particles in the LHC – Why is it that muons travel at the speed they do?,
        • Compare your results with results of your own muon velocity measurements with the CosMO or Kamiokannen experiments.