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Shower of Knowledge

ROOT data format description


These are the data which are recorded and stored for each detected event.

*************************************************
General name of the data block (Root Tree): LIVNI
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Event ID/I (Event number)
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Station properties (data related to the entire station)
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StationID/I - (Station unique ID)

--------------------- Station coordinates -----------------
Latitude/F - Station latitude, degrees
Longitude/F - Station longitude, degrees
Altitude/F - Station altitude, meters
************************************************
Information on events (cases of counter signal coincidences)
Event info (coincidence of hits in one station)
//************************************************
Event_time_sec/L: time of coincidence, seconds
Event_time_nanosec/L: time of coincidence,nanoseconds wrt PPS
Event_nsat/I: number of satellites in view
..................................
Event_nhits_1/I: number of hits in the first counter
Event_nhits_2/I: number of hits in the second counter
Hit_time_nanosec_1[Event_nhits_1]/L: time of hit in nanoseconds (rising edge) in the first counter
Hit_time_nanosec_2[Event_nhits_2]/L: time of hit in nanoseconds (rising edge) in the second counter
Hit_duration_1[Event_nhits_1]/L: duration of hit in the first counter in nanoseconds
Hit_duration_2[Event_nhits_2]/L: duration of hit in the second counter in nanoseconds


Now let us discuss each item.

It is quite obvious why two time values are needed for the description of an event. We get accurate data on the absolute time from the GPS satellites. This variable is designated as Event_time_sec, but these signals arrive only once a second. Therefore, the electronic unit has a subsystem for getting a more accurate time value within this one-second interval. Its operation is explained in the figure. 


 

 

The subsystem consists of a constantly operating very stable oscillator. In addition, there is a rather smart pulse counter. In fact, it is an ordinary counter, but is has some additional functions. First, it is reset. Each exact time signal resets the counter, and it starts counting from the very beginning (zero). In addition, it is necessary to record exact time for several quantities appearing at different time. Therefore, instead of termination of the counting process as usual, there is possibility of memorizing the current counter reading at a necessary moment of time (on arrival of the command signal triggering this operation) and storing several these readings in a special register. The first command to register the current time comes from the event trigger (the time of coincidence of signals from our two scintillation counters). And this quantity is designated in the data format asEvent_time_nanosec. . Thus, the exact time of event occurrence in our station is defined as 
Exact event time = Event_time_sec + Event_time_nanosec.

The next quantity,Event_nsat, is the number of satellites within the visibility range of the station antenna at the moment. This value, like Event_time_sec, is obtained from the GPS receiver.

The last data block from the data format: :

Caption Meaning
Event_nhits_1 Number of hits in the first counter
Event_nhits_2 Number of hits in the second counter
Hit_time_nanosec_1[Event_nhits_1] Time of hit in nanoseconds (rising edge) in the first counter
Hit_time_nanosec_2[Event_nhits_2] Time of hit in nanoseconds (rising edge) in the second counter
Hit_duration_1[Event_nhits_1] Duration of hit in the first counter in nanoseconds
Hit_duration_2[Event_nhits_2] Duration of hit in the second counter in nanoseconds.

 

To understand what it is, you have to recall that we want, on the one hand, to measure exactly the time when the event occurs (as much as possible with the available equipment) and, on the other hand, to select events that occur in our counters within a certain rather large time interval. We usually set it as ± 1 µs (this time can be changed and set in the electron unit manager). That is, if we want to select (trigger) all events in which the signals appearing in our two counters differ in time by no more than ± 1 1 µs, the ± sign arises because we do not know the signal in which of the counters will be the first to appear. But who told us that no other signal can appear in out counters within this time interval? What these signals come from, background or a real particle, we will find out later during the thorough data processing. Now our task is to record all these cases. Thus, we have the first two values Event_nhits_1 and Event_nhits_2, which show the total number of signals that appeared in the first and second counters. But if we allow for several subevents within one event, the above exact time measurement scheme should be extended because now we have to record not only the time of the “event” but also exact times of all signals in it. As a result, there arise the variables Hit_time_nanosec_1[Event_nhits_1]and Hit_time_nanosec_2[Event_nhits_2]. Their names are long yet clear: the time of the hit in the first counter [the number of this hit in the event] and in the second counter. Note that it is not simply a quantity but rather a one-dimensional array and the index in the brackets can vary from 1 to Event_nhitsnhits (1 or 2 depending on the detector number). The next figure is actually the same as the previous one, but with a larger time scale in the region where the event occurred (near the red pulse in the series of the oscillator signals). The new time scale is shown by the thin red arrow, 1µs. At the bottom left, both our detectors are shown. In this invented event, the first signals appears in the second counter, and in our coincidence interval it is only one (green line) whereas in the first counter there are two signals (red line). All these three signals are “photographed” and the number of oscillator pulses counted by the counter by the time of the arrival of the signals is memorized. This gives rise to the variables Hit_time_nanosec_1[1], Hit_time_nanosec_1[2] and Hit_time_nanosec_2[1]in the data for our event. In addition, due to a special circuit, there arise durations of the three signals of interest Hit_duration_1[1], Hit_duration_1[2] and Hit_duration_2[1]. The figure shows how they are formed.

 


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