Cosmic ray detection array triggering method based on density clustering

Abstract

The invention discloses a cosmic ray detection array triggering method based on density clustering, and the method comprises the steps: carrying out the threshold-crossing discrimination of the amplitudes of input signals of all channels of a cosmic ray detection array at an initial a moment, and obtaining channels with the signal amplitudes exceeding a set threshold value; generating a neighborhood of which the radius of the threshold channel is R, and obtaining a channel number corresponding to the neighborhood according to the channel arrangement layout of the cosmic ray detection array; counting the sum NL of the number of threshold-crossing channels which accumulatively appear in the neighborhood in a time window with the length of L, comparing the neighborhood density Mb with the set neighborhood minimum density Mmin, and judging whether a trigger signal is generated or not according to a comparison result; and obtaining the number of all channels in the neighborhood of the over-threshold channel corresponding to the triggering moment, and transmitting the number to a back-end system. According to the method, the problem that the triggering efficiency of a triggering algorithm based on multiple numbers or adjacent pixel positions on a physical case is low can be solved, and the triggering efficiency of a system on the physical case is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of data real-time triggering and selection, and particularly to a triggering method for a cosmic ray detection array based on density clustering. Background Art

[0002] The trigger electronics system plays a crucial role in particle physics experiments. In order to screen out the effective event data concerned by physicists from the raw data read out by the front-end electronics and eliminate many unnecessary redundant and noise data, it is necessary to achieve a high trigger efficiency and a low false judgment rate. The main basis of the trigger algorithm is the different characteristics of effective physical events and noise, that is, the signal amplitude of effective physical events is large, almost instantaneous in time, and forms a local dense cluster in space; while the noise signal has a small amplitude, changes slowly in time, and is more evenly distributed in space.

[0003] Particle physics experiments often adopt a trigger algorithm based on multiplicity or based on adjacency, that is, within a set time window, if the total number of pixels with signal amplitude exceeding the threshold exceeds the set multiplicity threshold, or the pixels with signal amplitude exceeding the threshold are adjacent in space, a trigger is generated. Common trigger algorithms include simple multiplicity trigger, overlapping partition multiplicity trigger, and nneighbor trigger. In order to reduce the false trigger of noise, the simple multiplicity trigger algorithm needs to set a high multiplicity threshold, resulting in the inability to screen out lower-energy events; compared with the simple multiplicity trigger, the overlapping partition multiplicity trigger reduces the possibility of accidental coincidence of noise pixels that are far apart, but there may still be accidental coincidence of noise within the partition; the nneighbor trigger utilizes the characteristic that effective events are compactly distributed in space, but for lower-energy events, the over-threshold pixels may only be close but not adjacent, or the adjacent quantity is small, resulting in either they cannot be screened out using the adjacent condition, or only a lower n value can be used, and since the trigger selection condition is applied to all channels, the false trigger rate of accidental coincidence of noise will also increase significantly. In summary, the existing trigger algorithms in the prior art have poor performance in screening effective physical events, are not flexible enough, and cannot achieve a high trigger efficiency and a low false judgment rate. Summary of the Invention

[0004] The purpose of the present invention is to provide a triggering method for a cosmic ray detection array based on density clustering, which can solve the problem that the trigger efficiency of the trigger algorithm based on multiplicity or pixel position adjacency for physical events is low, and effectively improve the trigger efficiency of the system for physical events.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A triggering method for a cosmic ray detection array based on density clustering, the method includes:

[0007] Step 1: Perform over-threshold discrimination on the input signal amplitudes of all channels of the cosmic ray detection array at the initial time a to obtain the channels whose signal amplitudes exceed the set threshold, that is, the numbers of the over-threshold channels and the number N of over-threshold channels a ;

[0008] Step 2: Generate a neighborhood with a radius of R for the over-threshold channels, and obtain the corresponding channel numbers of the neighborhood according to the channel arrangement layout of the cosmic ray detection array;

[0009] Step 3: Count the sum N of the cumulative number of over-threshold channels that have appeared in the neighborhood within a time window with a length of L, and calculate the neighborhood density M at time b L , and compare the neighborhood density M b with the set minimum neighborhood density M b to determine whether a trigger signal is generated according to the comparison result; min Step 4: According to the trigger signal, obtain all the channel numbers within the neighborhood of the over-threshold channels corresponding to the trigger time and transmit them to the backend system.

[0010] It can be seen from the above technical solutions provided by the present invention that the above method can solve the problem that the trigger algorithms based on multiplicity or pixel position adjacency have low trigger efficiency for physical events, and effectively improve the trigger efficiency of the system for physical events.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0012]

[0013] Figure 1 is a schematic flow chart of a cosmic ray detection array trigger method based on density clustering provided by an embodiment of the present invention;

[0014] Figure 2 is a schematic plan view of an imaging atmospheric Cherenkov telescope as an example of the present invention;

[0015] Figure 3 is a conceptual schematic diagram of the trigger process as an example of the present invention;

[0016] Figure 4 is a schematic diagram of a non-triggering situation as an example of the present invention;

[0017] Figure 5 is a schematic diagram of a triggering situation as an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, which does not constitute a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0019] As Figure 1 shown in the schematic flowchart of the cosmic ray detection array trigger method based on density clustering provided by the embodiment of the present invention, the method includes:

[0020] Step 1: Perform over-threshold discrimination on the input signal amplitudes of all channels of the cosmic ray detection array at the initial a moment to obtain the channels whose signal amplitudes exceed the set threshold, that is, the numbers of the over-threshold channels and the number N of the over-threshold channels a ;

[0021] In this step, first set three parameters: the signal amplitude threshold Threshold of the cosmic ray detection array channel, the neighborhood radius R of the over-threshold channels, and the minimum neighborhood density M min ;

[0022] Then store the numbers of the over-threshold channels;

[0023] And count the number N of the over-threshold channels at the initial a moment a .

[0024] Step 2: Generate a neighborhood with a radius of R for the over-threshold channels, and obtain the corresponding channel numbers of the neighborhood according to the channel arrangement layout of the cosmic ray detection array;

[0025] In this step, with each over-threshold channel as the center, extend a distance R around to obtain a neighborhood with a radius of R for the over-threshold channels, and obtain the numbers of all channels within the neighborhood according to the channel arrangement layout of the cosmic ray detection array.

[0026] Step 3: Count the sum N of the cumulative number of over-threshold channels that have appeared within the neighborhood within a time window with a length of L L , calculate the neighborhood density M at the b moment b , and compare the neighborhood density M b with the set minimum neighborhood density M min to determine whether a trigger signal is generated according to the comparison result;

[0027] In this step, the time window is a period starting from the initial moment a and ending at moment b, where a < b. The time window does not include moment a but includes moment b. The length L of the time window is equal to the value obtained by subtracting moment a from moment b, i.e., L = b – a. The sum N of the number of over-threshold channels that have cumulatively appeared in the neighborhood within this time window is counted. L , and the neighborhood density M at moment b is calculated. b , and the neighborhood density M is defined. b = N L / N a ;

[0028] The calculated neighborhood density M b is compared with the set minimum neighborhood density M min . If M b is greater than or equal to M min , it indicates that a cluster, i.e., a valid physical event, has been recognized, and a trigger signal is generated. The trigger moment is moment b minus the time window length L, i.e., moment a. Otherwise, no trigger signal is generated, and step 3 is re-executed with the moment incremented by one, i.e., the situation between moment a + 1 and moment b + 1 is judged, and so on.

[0029] Step 4: According to the trigger signal, obtain all the channel numbers within the neighborhood of the over-threshold channels corresponding to the trigger moment and transmit them to the backend system.

[0030] In this step, all the channel data that have been triggered, i.e., recognized as valid, are obtained and uploaded to the backend.

[0031] It should be noted that the content not described in detail in the embodiments of the present invention belongs to the prior art well-known to those skilled in the art.

[0032] For the convenience of more clearly understanding the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. This example is applicable to the channel signals of a PMT (Photo Multiplier Tube) or SiPM (Silicon Photomultiplier) array.

[0033] Taking the imaging atmospheric Cherenkov telescope technology commonly used in particle physics experiments as an example, such as Figure 2The following is a schematic plan view of the imaging atmospheric Cherenkov telescope in the example of the present invention. The entire camera plane of the telescope is approximately hexagonal, including 61 channels, numbered 0, 1, 2... 60 in sequence from the inside out. A 64-bit register is used to represent whether the input signals of the 61 channels cross the threshold (1 for crossing the threshold, otherwise 0), and the highest 3 bits of the register are fixed values of 0. In this example, 3 64-bit registers are required for calculation, namely the register overthre_reg_a representing the channel threshold crossing situation at time a, the register neighbor_reg representing the neighborhood situation of the threshold crossing channels, the register overthre_reg_L representing the channel threshold crossing situation between time a and time b (i.e., within a time window of length L), and the register overthre_in_neighbor representing the channel threshold crossing situation within the neighborhood between time a and time b.

[0034] The following method is used to evaluate the distance between two channels: For the channel numbered 0, the distance between the channels numbered 1, 2, 3, 4, 5, 6 and it is 1; the distance between the channels numbered 7, 8, 9... 18 and it is 2; and for the next outer ring, the distance is 3, and so on.

[0035] As Figure 3 The following is a conceptual schematic view of the triggering process in the example of the present invention, including 2 threshold crossing channels (numbered 7 and 15) that appear at time a, the neighborhood with a radius R of 1 of the threshold crossing channels (including the channels numbered 1, 5, 7, 8, 14, 15, 16, 18, 19, 20, 30, 31, 32, 36, with slashes), the threshold crossing channels that appear between time a and time b (the channels numbered 1, 5, 7, 8, 15, 30 are within the neighborhood, with slashes; the channels numbered 23, 26 are not within the neighborhood).

[0036] As Figure 4 The following is a schematic view of a non-triggering situation in the example of the present invention. A lower-energy effective physical event causes the threshold crossing channels to be only close but not adjacent, or the number of adjacent channels is small. In this example, the set parameters are: the neighborhood radius R is 1, and the minimum neighborhood density M min is 4.

[0037] At time a, the channel numbered 0 crosses the threshold, so overthre_reg_a = 64'h0000_0000_0000_0000_0000_0000_0000_0001; the neighborhood of the channel numbered 0 includes the channels numbered 0, 1, 2, 3, 4, 5, 6, so neighbor_reg = 64'h0000_0000_0000_0000_0000_0000_0000_007F.

[0038] Between time a and time b, channels numbered 5, 6, 8, and 10 cross the threshold, so overthre_reg_L = 64'h0000_0000_0000_0000_0000_0000_0000_0561;

[0039] Among these channels, only 3 channels numbered 0, 5, and 6 are within the neighborhood. This is equivalent to performing a bitwise AND operation (&) on overthre_reg_L and neighbor_reg to obtain overthre_in_neighbor = 64'h0000_0000_0000_0000_0000_0000_0000_0031. There are 3 bits set to 1 in this 64-bit register. Therefore, between time a and time b, the sum N of the number of channels that crossed the threshold within the neighborhood L is 3. Calculate the neighborhood density M b = N L / N a = 3 / 1 = 3, which is less than the set minimum neighborhood density M min , so no trigger signal is generated.

[0040] As Figure 5 shown in the schematic diagram of a triggering case of an example of the present invention, for the same relatively low-energy physical event, as long as the neighborhood radius R is appropriately increased, triggering can be achieved while maintaining the same minimum neighborhood density M min value. Since the neighborhood range is only slightly expanded, when applying the new parameters within this small range, the false trigger rate due to accidental coincidence of noise hardly increases. The parameters set in this example are: the neighborhood radius R is 2, and the minimum neighborhood density M min is 4.

[0041] At time a, channel numbered 0 crosses the threshold, so overthre_reg_a = 64'h0000_0000_0000_0000_0000_0000_0000_0001; the neighborhood of channel numbered 0 includes channels numbered 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, so neighbor_reg = 64'h 0000_0000_0000_0000_0000_0000_0007_FFFF.

[0042] Between time a and time b, channels numbered 5, 6, 8, and 10 cross the threshold, so overthre_reg_L = 64'h0000_0000_0000_0000_0000_0000_0000_02B1;

[0043] Among these channels, 5 channels numbered 0, 5, 6, 8, and 10 are all within the neighborhood. Similarly, overthre_in_neighbor = overthre_reg_delta & neighbor_reg = 64'h0000_0000_0000_0000_0000_0000_0000_02B1, and there are 5 bits set to 1 in this 64-bit register. Therefore, the sum N of the number of over-threshold channels that have occurred within the neighborhood between time a and time b L is 5, and the neighborhood density M is calculated b = N L / N a = 5 / 1 = 5, which is greater than or equal to the set minimum neighborhood density M min , so a trigger signal is generated.

[0044] In addition, those of ordinary skill in the art can understand that all or part of the steps in implementing the methods of the above embodiments can be completed by instructing relevant hardware through a program, and the corresponding program can be stored in a computer-readable storage medium. The storage media mentioned above can be a read-only memory, a magnetic disk, an optical disc, or the like.

[0045] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The information disclosed in the background art section of this article is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art.

Claims

1. A cosmic ray detection array triggering method based on density clustering, characterized in that: The method comprises: Step 1: Perform threshold screening on the input signal amplitudes of all channels of the cosmic ray detection array at the initial time a, and obtain the channels whose signal amplitudes exceed the set threshold, that is, the number of the over-threshold channels and the number of over-threshold channels N a ; Step 2: Generate a neighborhood with a radius of R of the over-threshold channel, and obtain the channel number corresponding to the neighborhood according to the channel arrangement layout of the cosmic ray detection array; Step 3: Count the total number of over-threshold channels N that have appeared in the neighborhood within the time window of length L. L , calculate the neighborhood density M at time b b , the neighborhood density M b and the set minimum neighborhood density M min Compare, and determine whether to generate a trigger signal based on the comparison result; Step 4: According to the trigger signal, the number of all channels in the neighborhood of the over-threshold channel corresponding to the trigger moment is obtained and transmitted to the back-end system.

2. The cosmic ray detection array triggering method based on density clustering according to claim 1, characterized in that: In step 1, three parameters are first set: the signal amplitude threshold Threshold of the cosmic ray detection array channel, the neighborhood radius R of the over-threshold channel, and the minimum neighborhood density M min ; Then store the number of the over-threshold channel; And count the number of channels N that cross the threshold at the initial time a a .

3. The cosmic ray detection array triggering method based on density clustering according to claim 1, characterized in that: In step 2, each cross-threshold channel is taken as the center and the distance R is extended to the surrounding area to obtain a neighborhood with a radius of R of the cross-threshold channel, and the numbers of all channels in the neighborhood are obtained according to the channel arrangement layout of the cosmic ray detection array.

4. The cosmic ray detection array triggering method based on density clustering according to claim 1, characterized in that: In step 3, the time window is a period of time starting from the initial time a and ending at time b, a<b, the time window does not include time a, but includes time b; the length of the time window L is equal to the value of time b minus time a, that is, L=b–a; the total number of over-threshold channels N that have appeared in the neighborhood within the time window is counted L , calculate the neighborhood density M at time b b , define the neighborhood density M b =N L / N a ; Compare the calculated neighborhood density M b And the minimum neighborhood density M min , if M b Greater than or equal to M min , indicating that a cluster, i.e., a valid physical event, is identified, a trigger signal is generated, and the trigger time is time b minus the time window length L, i.e., time a; otherwise, no trigger signal is generated, and step 3 is executed again, and the time is increased by one, i.e., the situation between time a+1 and time b+1 is judged, and so on.

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