Experimental evidence for the sensitivity of the air-shower radio signal to the longitudinal shower development

We observe a correlation between the slope of radio lateral distributions and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events. The radio lateral distributions are measured with LOPES, a digital radio interferometer colocated with the multidetector-air-shower array KASCADE-Grande, which includes a muon-tracking detector. The result proves experimentally that radio measurements are sensitive to the longitudinal development of cosmic-ray air showers. This is one of the main prerequisites for using radio arrays for ultra-high-energy particle physics and astrophysics.

Figure 1

Shower cores of the 59 selected events measured simultaneously with the east-west aligned LOPES antennas, the KASCADE-Grande particle-detector array, and the MTD. Because of a reconfiguration of LOPES, 15 of the 30 antennas were only available for part of the events.

Figure 2

Example for a radio lateral distribution measured with LOPES.

Figure 3

Mean muon pseudorapidity and the slope parameter of the radio lateral distribution for the 59 events.

Figure 4

Dependencies of the two observables, mean muon pseudorapidity (left panels) and slope parameter of the radio lateral distribution (right panels), on the mean distance from the measured muons to the air-shower axis (top panels) and the shower inclination (bottom panels). The slopes of the fitted lines are used for correction of the observables.

Figure 5

Correlation between the mean muon pseudorapidity and slope of the radio lateral distribution after correcting for the distance to the shower axis and the shower inclination.