Primary and Secondary
All stations have HiSPARC Primary electronics that reads out 2 detectors. Stations that have 4 detectors also have HiSPARC Secondary electronics, linked to the Primary, to read out the other two detectors.
HiSPARC Public Database help
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
The time, relative to the start of the signal trace, at which the first signal is seen in a detector. With these arrival times we know in which order the detectors were hit and can reconstruct the shower direction. The following graph shows the detector signal traces 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.
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 (< 200 µs) it is likely from the same air shower.
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.
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 electronics
This controls the PMT voltages and converts their signals into digital values. It constantly samples the PMT. When signals cross the thresholds and the trigger conditions are met it will store the signals as an event. After combining this with a timestamp from the GPS this data is sent to the PC.
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 is triggered. This is used to filter low signals from background sources.
Trigger
When signals from at least 2 detectors go over the thresholds within a short time window the event is recorded. If only one detector is hit it is ignored, because it may eb background radiation.
Trigger Time
The time, relative to the start of the signal trace, at which the trigger took place. This allows you to relate the arrival times in detectors to the GPS timestamp.
Photo Multiplier Tube (PMT)
The PMT converts the light emitted by the scintillator into an electric signal for the HiSPARC electronics.
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 occurred 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.