Public Database

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 contols 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.

Master and Slave

All stations have HiSPARC Master electronics that reads out 2 detectors. Stations that have 4 detectors also have HiSPARC Slave electronics, linked to the Master, 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 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 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.