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Here is an overview of the various terms used on the HiSPARC data pages. Each term is accompanied by an explanation. For more information about the Public Database you can have a look at the documentation.

Arrival time

This is the time at which the first signal from a particle is seen in a detector. With these arrival times we know in which order the detectors were hit and can reconstruct the position on the sky where the shower came from. The following graph shows the detector signals of one event, the arrival times are indicated with the vertical lines.

Cluster

Our detectors are grouped by clusters. A cluster is often a city or region (e.g. Groningen or Bristol). This makes it easy to find stations that are close together.

Event

When a detector station is triggered and measures signals that indicate a cosmic-ray air shower, we call that an event.

Event rate

This is a value that expresses how many events occur in a given time period. For example, a 2-detector station measures approximately 1100 events per hour.

Coincidence

When different detector stations measure the same event this is called a coincidence. It is possible to determine if stations measured the same event by comparing the GPS timestamps of events. If they are close together it is likely from the same air shower.

Histogram

The possible values of some variable (e.g. pulseheight) are split into many ranges (bins), then a list of these values is sorted into the correct bins. Then you have will have a number of 'counts' in each bin, which tells you how often a certain value occurs.

HiSPARC box

This electronics box converts the electric signals from the PMTs into digital values. It constantly reads out the PMT. When the signals crosses the thresholds and the trigger conditions are met it will store the signals as an event. It will then combine this with a timestamp from the GPS and send this data to the PC.

Master and Slave

All stations have one Master electronics box that reads out 2 detectors. Stations that have 4 detectors also have a Slave box to read out the other two detectors.

Minimum Ionizing Particle (MIP)

This refers to the most probable energy that a particle will release in a scintillator. Since this is the most probable value (MPV) this can be found by looking for a peak in the pulseheight histogram. This point is indicated in the graph, here the value is 155 mV.

Nanosecond (ns)

We need to measure the arrival times of the particles in the detectors with very high accuracy. With these accurate times we can do angle reconstruction and find coincidences. So the times are measured with nanosecond precision, a nanosecond is equal to 10−9 s or 1/1 000 000 000 s

Threshold

This indicates the minimum signal strength that is needed before a detector can be triggered. This is used to filter low signals from background sources.

Photo Multiplier Tube (PMT)

When particles in the air shower traverse the scintillator it emits light. The PMT converts the light from the scintillator into an electric signal for the HiSPARC box.

Pulseheight

The pulseheight histogram counts how often a certain maximum height was seen in the signals of the measured events. The pulseheight is an indication for the number of particles that hit the detector, on average this is 140 mV per particle (higher signal = more particles). The following graph shows how this value is determined from the signals of a single event.

Pulseintegral

The pulseintegral is determined by taking the integral of the signal trace. The pulseintegral histogram shows how often a value occured for a detector for all measured events. This graph shows how this value is determined.

Zenith

This is the angle between a point on the sky (source of cosmic rays) and the point straight up from the observers (detectors) point of view.

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