A system for measuring spin polarization of a muon

Abstract

The application relates to the technical field of primordial muon detection, and discloses a primordial muon spin polarization measurement system, which comprises a primordial muon momentum detection module, a primordial muon stopping target and a positron and electron detection module. The primordial muon momentum detection module is used for detecting the momentum information of a primordial muon passing through the primordial muon momentum detection module. The primordial muon stopping target is arranged below the primordial muon momentum detection module, and the axis of the primordial muon stopping target extends along a first direction. The positron and electron detection module is arranged below the primordial muon momentum detection module, and the positron and electron detection module comprises a first positron and electron detection unit group and a second positron and electron detection unit group. The first positron and electron detection unit group, the primordial muon stopping target and the second positron and electron detection unit group are sequentially and spacedly arranged along the first direction. The first positron and electron detection unit group and the second positron and electron detection unit group each comprise a plurality of positron and electron detection units which are sequentially arranged along the circumference of the axis of the primordial muon stopping target.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of muon detection, and particularly relates to a muon spin polarization measurement system. BACKGROUND

[0002] Muons are the second generation leptons in the Standard Model of particle physics, with a mass of about 105.67 MeV and a unit of negative charge. Muons are similar to electrons in many ways except that they are more than 200 times heavier. Since their first observation in cosmic rays by Anderson in the 1930s, muons have played an extremely important role in particle physics and even the entire field of physics. Muons are mainly produced through the decay of heavier particles such as pions or kaons. At present, a few particle physics accelerators can produce muons with a certain energy. However, the properties of cosmic muons (primary muons) are still not very clear. Primary muons are muons produced by the interaction of primary cosmic rays (mainly protons) and atomic nuclei in the Earth's atmosphere. Since the energy range of primary cosmic rays is very wide, the energy range of primary muons is also very wide. The rest lifetime of muons is about 2.2 microseconds, but muons with higher energy can reach the ground under the influence of relativistic effects. Therefore, primary muons are one of the main components of cosmic rays observed on the ground.

[0003] For primary muons, in addition to the most basic energy, another important property is spin polarization. Spin polarization of a particle is the projection of spin in the momentum direction. Since the Standard Model of particle physics requires that there are only neutrinos with opposite momentum and spin directions and antineutrinos with the same momentum and spin directions in nature. Therefore, the spin polarization of muons produced by the decay of pions and kaons is also determined under the influence of energy-momentum conservation. In the accelerator, almost all muons come from the decay of pions and kaons. At the same time, the transport distance of muons is short, and the inside of the accelerator pipe is in a vacuum environment, so the spin polarization of most muons in the accelerator is determined. However, the spin polarization of primary muons is much more complicated. First, not all primary muons come from the decay of pions and kaons. If the primary muons come from some heavier mesons, their spin polarization properties are uncertain. Secondly, primary muons need to pass through the entire atmosphere to reach the ground, that is, primary muons will interact with atmospheric particles many times during the process of passing through the atmosphere, thereby changing the original spin polarization properties.

[0004] The reason why the spin polarization of muons is an important physical quantity is that the spatial distribution of the Michel electrons (or positrons) produced by the decay of muons is affected by the spin direction. The momentum direction of the Michel electrons tends to be aligned with the spin direction of the muons. Therefore, by analyzing the spatial distribution of the Michel electrons produced by the decay of cosmic muons, the spin direction of the cosmic muons can be obtained. Since the spin direction of muons is sensitive to magnetic fields, by measuring the spin direction of muons, the magnetic field at the decay site of muons can be indirectly measured.

[0005] The measurement of the spin polarization of cosmic muons has strong practical significance. First, the spin polarization of cosmic muons can reflect the proportion of the products of the interaction between primary cosmic rays and the atmosphere, such as the proportion of pions and K mesons. By measuring the spin polarization of cosmic muons, the credibility of existing cosmic ray models can be significantly improved. Second, the measurement of the spin polarization of cosmic rays can help understand the change rule of spin polarization in the interaction process and thus help improve the spin polarization rate of muons in accelerators. In addition, the current muon resources in the world are very limited, and most muon application scenarios have high requirements for the spin polarization properties of muons. Therefore, by measuring the spin polarization of cosmic rays, researchers can use cosmic muons as a muon source to develop muon-related applications. In general, the polarization of cosmic muons is a physical quantity with great measurement value.

[0006] Currently, there are two main schemes for measuring the spin polarization of cosmic muons. The first scheme is to use a large water Cherenkov detector to measure cosmic muons. In 2024, Kitageawa et al. used the Super-Kamiokande water Cherenkov detector in Japan to measure the spin polarization of cosmic muons in the local area. Finally, they obtained the spin polarization characteristics of cosmic muons with a momentum of 0.3 GeV / c at sea level. The second scheme is an older scheme that uses a multi-layer scintillator detector to study the spin polarization of muons. This scheme uses the interaction between the scintillator and the cosmic muon to stop the cosmic muon in a certain layer of the scintillator, such as the Nth layer. Then, it observes whether there is a trigger of the N+1 or N-1 layer of the scintillator within a certain time. By observing the up-down asymmetry of the decay products, it attempts to restore the "spin polarization" of cosmic muons.

[0007] Water Cherenkov detectors often require a large amount of pure water and a large number of photomultiplier tubes. Therefore, once a water Cherenkov detector is built, it is difficult to move. As can be seen, the water Cherenkov detector scheme has a very high construction and maintenance cost, and the energy consumption is also high. In addition, if the water Cherenkov detector is installed underground, the detector can only detect high-energy cosmic muons and cannot observe low-energy cosmic muons.

[0008] There are some technical shortcomings in using only the multi-layer scintillator to measure the up-down asymmetry of the primordial muon decay product. First, using only the multi-layer scintillator cannot distinguish the momentum size and direction of the primordial muon, that is, the momentum-dependent spin polarization of the primordial muon cannot be obtained. Second, since the spatial distribution of the Michel electron is an axisymmetric distribution with the momentum direction of the primordial muon as the axis, at least two degrees of freedom are needed to describe the spatial distribution of the Michel electron. Therefore, only measuring the up-down asymmetry will result in the loss of the spatial distribution degree of freedom. In general, the measurement scheme using only the multi-layer scintillator will lose a large amount of information, so that it is almost impossible to measure the acceptable precision of the spin polarization of the primordial muon.

[0009] Therefore, there is an urgent need for a primordial muon spin polarization measurement system to solve the above problems. SUMMARY

[0010] The purpose of the present application is to provide a primordial muon spin polarization measurement system that can effectively measure the spin polarization of the primordial muon.

[0011] To achieve this purpose, the present application adopts the following technical solutions:

[0012] A primordial muon spin polarization measurement system, comprising:

[0013] A primordial muon momentum detection module for detecting the momentum information of the primordial muon passing through the primordial muon momentum detection module;

[0014] A primordial muon stopping target arranged below the primordial muon momentum detection module for stopping part of the primordial muon passing through the primordial muon momentum detection module on the primordial muon stopping target, the axis of the primordial muon stopping target extending along a first direction, the first direction being the height direction of the primordial muon spin polarization measurement system;

[0015] A positron-electron detection module arranged below the primordial muon momentum detection module, the positron-electron detection module comprising a first positron-electron detection unit group and a second positron-electron detection unit group, the first positron-electron detection unit group, the primordial muon stopping target and the second positron-electron detection unit group being sequentially arranged along the first direction, the first positron-electron detection unit group and the second positron-electron detection unit group each comprising a plurality of positron-electron detection units arranged sequentially along the circumferential direction of the axis of the primordial muon stopping target, the positron-electron detection units being used to detect the Michel electron generated by the decay of the primordial muon stopped on the primordial muon stopping target.

[0016] As an improvement of the above technical solution, the primordial muon momentum detection module comprises two first scintillator detectors, the two first scintillator detectors are arranged at intervals along the first direction, and the primordial muon momentum detection module is used for monitoring the position and time of the primordial muon passing through each first scintillator detector.

[0017] As an improvement of the above technical solution, the first scintillator detector comprises:

[0018] a first scintillator plate arranged perpendicularly to the first direction;

[0019] a light guide array plate covering the top surface of the first scintillator plate;

[0020] a plurality of transverse wavelength shift optical fibers, each of which is arranged in the light guide array plate and extends along a second direction, the second direction is perpendicular to the first direction, and the plurality of transverse wavelength shift optical fibers are arranged at intervals along a third direction, the second direction and the first direction are both perpendicular to the third direction;

[0021] a plurality of longitudinal wavelength shift optical fibers, each of which is arranged in the light guide array plate and extends along the third direction, and the plurality of longitudinal wavelength shift optical fibers are arranged at intervals along the second direction;

[0022] a first photoelectric converter, the first end of each transverse wavelength shift optical fiber is connected with the first photoelectric converter;

[0023] a second photoelectric converter, the first end of each longitudinal wavelength shift optical fiber is connected with the second photoelectric converter.

[0024] As an improvement of the above technical solution, the primordial muon stopping target is cylindrical.

[0025] As an improvement of the above technical solution, the positron-electron detection unit comprises a plurality of second scintillator detectors, the second scintillator detector comprises a second scintillator plate and a third photoelectric converter, and the two ends of the second scintillator plate are provided with the third photoelectric converter, and the plurality of second scintillator detectors of each positron-electron detection unit are arranged in sequence along a direction perpendicular to the first direction.

[0026] As an improvement of the above technical solution, it further comprises an anticoincidence detection module, which is used for detecting the primordial muon that reaches the positron-electron detection module or the primordial muon stopping target without passing through the primordial muon momentum detection module.

[0027] As the improvement of the above technical scheme, the anti-coincidence detection module comprises a plurality of third scintillator detectors which are arranged along the circumference of the cosmic muon stopping target and are arranged on the side of the positron-electron detection unit away from the cosmic muon stopping target, and the third scintillator detector comprises a third scintillator plate and a fourth photoelectric converter, and the fourth photoelectric converter is arranged at both ends of the third scintillator plate.

[0028] As the improvement of the above technical scheme, the first scintillator plate, the second scintillator plate and the third scintillator plate are all plastic scintillators.

[0029] As the improvement of the above technical scheme, a cosmic muon energy reducer is further arranged above the cosmic muon momentum detection module, and is used to reduce the kinetic energy of the cosmic muon passing through the cosmic muon energy reducer.

[0030] As the improvement of the above technical scheme, the cosmic muon energy reducer is a lead plate or a concrete plate, and the cosmic muon energy reducer is arranged perpendicularly to the first direction.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The cosmic muon spin polarization measurement system provided by the present application can detect the momentum information of the cosmic muon passing through the cosmic muon momentum detection module through the cosmic muon momentum detection module, stop part of the cosmic muon passing through the cosmic muon momentum detection module on the cosmic muon stopping target through the cosmic muon stopping target, detect the spatial distribution information of the Michel electron generated by the cosmic muon stopped on the stopping target through the first positron-electron detection unit group and the second positron-electron detection unit group arranged on the upper and lower sides of the cosmic muon stopping target and along the circumference of the cosmic muon stopping target, and then reconstruct the spin direction of the cosmic muon by using the spatial distribution information of the Michel electron, and further reconstruct the spin polarization of the cosmic muon by combining the spin direction of the cosmic muon with the momentum direction of the cosmic muon passing through the cosmic muon momentum detection module. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structure schematic diagram of the cosmic muon spin polarization measurement system provided by the embodiment of the present application;

[0034] Figure 2 is a partial structure schematic diagram (hidden part of the third scintillator detector) of the cosmic muon spin polarization measurement system provided by the embodiment of the present application;

[0035] Figure 3is a part structure schematic diagram of a primordial muon spin polarization measurement system provided by an embodiment of the present application (hides a primordial muon energy reducer, a primordial muon momentum detection module and part of a support module);

[0036] Figure 4 is a part structure schematic diagram of a first scintillator detector of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0037] Figure 5 is a structure schematic diagram of a positron-electron detection unit of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0038] Figure 6 is a structure schematic diagram of a primordial muon stopping target and a support rod of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0039] Figure 7 is a structure schematic diagram of an anticoincidence detection module and a second support plate of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0040] Figure 8 is a part structure schematic diagram of a third scintillator detector of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0041] Figure 9 is a part structure schematic diagram of a support module of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0042] Figure 10 is a structure schematic diagram of a first support plate of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0043] Figure 11 is a structure schematic diagram of a second support plate of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0044] Figure 12 is a structure schematic diagram of a third support plate of a primordial muon spin polarization measurement system provided by an embodiment of the present application;

[0045] Figure 13 is a framework of a multi-channel electronic system used by a positron-electron detection module of a primordial muon spin polarization measurement system provided by an embodiment of the present application.

[0046] In the figure:

[0047] 1, a primordial muon momentum detection module; 11, a first scintillator detector; 111, a first scintillator plate; 112, a light guide array plate; 113, a first adapter; 114, a second adapter;

[0048] 2, a primordial muon stopping target;

[0049] 3, positron-electron detection module; 31, first positron-electron detection unit group; 32, second positron-electron detection unit group; 301, positron-electron detection unit; 3011, second scintillator detector;

[0050] 4, anticoincidence detection module; 41, third scintillator detector; 411, third scintillator plate;

[0051] 5, support module; 51, support frame; 511, support crossbeam; 52, first support plate; 53, second support plate; 54, third support plate; 55, support rod;

[0052] 6, cosmic muon energy reducer. DETAILED DESCRIPTION

[0053] The specific embodiments of the present application will be further described in conjunction with the drawings and examples. The following examples are used to illustrate the present application, but are not used to limit the scope of the present application.

[0054] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0055] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include the direct contact of the first and second features, or can include the contact of the first and second features through another feature between them. Moreover, the "upper", "upper" and "upper" of the first feature to the second feature includes the vertical and oblique above of the first feature to the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "below", "below" and "below" of the first feature to the second feature includes the vertical and oblique below of the first feature to the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0056] In the description of the present embodiment, the terms "upper", "lower", "right", and other orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only used to distinguish in the description, and have no special meaning.

[0057] As Figures 1-8 shown, the muon spin polarization measurement system of the embodiment of the application includes a muon momentum detection module 1, a muon stopping target 2 and a positron and electron detection module 3. The muon momentum detection module 1 is used to detect the momentum information of the muon passing through the muon momentum detection module 1. The muon stopping target 2 is arranged below the muon momentum detection module 1 and is used to stop part of the muon passing through the muon momentum detection module 1 on the muon stopping target 2. The axis of the muon stopping target 2 extends along a first direction, and the first direction is the height direction of the muon spin polarization measurement system. The positron and electron detection module 3 is arranged below the muon momentum detection module 1. The positron and electron detection module 3 includes a first positron and electron detection unit group 31 and a second positron and electron detection unit group 32. The first positron and electron detection unit group 31, the muon stopping target 2 and the second positron and electron detection unit group 32 are sequentially and spacedly arranged along the first direction from top to bottom. The first positron and electron detection unit group 31 and the second positron and electron detection unit group 32 each include a plurality of positron and electron detection units 301 arranged along the circumference of the axis of the muon stopping target 2. The positron and electron detection units 301 are used to detect the Michel electrons generated by the decay of the muon stopped on the muon stopping target 2.

[0058] The muon spin polarization measurement system provided by the embodiment detects the momentum information of the muon passing through the muon momentum detection module 1 through the muon momentum detection module 1, stops part of the muon passing through the muon momentum detection module 1 on the muon stopping target 2 through the muon stopping target 2, detects the Michel electrons generated by the decay of the muon stopped on the stopping target through the first positron and electron detection unit group 31 and the second positron and electron detection unit group 32 arranged on the upper and lower sides of the muon stopping target 2 and along the circumference of the axis of the muon stopping target 2, obtains the spatial distribution information of the Michel electrons, and thus reconstructs the spin direction of the muon using the spatial distribution information of the Michel electrons, and further reconstructs the muon spin polarization through the spin direction of the muon combined with the momentum direction of the muon passing through the muon momentum detection module 1.

[0059] Further, as Figure 1 and Figure 2As shown, the cosmic muon momentum detection module 1 includes two first scintillator detectors 11, the two first scintillator detectors 11 are arranged in a first direction, and the cosmic muon momentum detection module 1 is used to monitor the position and time of the cosmic muon passing through each first scintillator detector 11 (it should be noted that the time of the cosmic muon passing through each first scintillator detector 11 refers to the two times of the cosmic muon passing through the two first scintillator detectors 11). In this embodiment, the momentum information is the direction of the cosmic muon momentum, and in other embodiments, the momentum information can also include the magnitude of the cosmic muon momentum. Specifically, by the position and time of the cosmic muon passing through the two first scintillator detectors 11, the speed (including magnitude and direction) of the cosmic muon can be obtained, and the mass of the cosmic muon is a known quantity, so the magnitude and direction of the cosmic muon speed are also the magnitude and direction of the cosmic muon momentum.

[0060] Further, as shown, Figure 4 As shown, the first scintillator detector 11 includes a first scintillator plate 111, a light guide array plate 112, a plurality of transverse wavelength shift optical fibers, a plurality of longitudinal wavelength shift optical fibers, a first photoelectric converter, and a second photoelectric converter. The first scintillator plate 111 is arranged perpendicular to the first direction. The light guide array plate 112 is covered on the top surface of the first scintillator plate 111. The transverse wavelength shift optical fibers are all arranged in the light guide array plate 112 and extend along the second direction, the second direction is perpendicular to the first direction, and the plurality of transverse wavelength shift optical fibers are arranged in the third direction. The longitudinal wavelength shift optical fibers are all arranged in the light guide array plate 112 and extend along the third direction, and the plurality of longitudinal wavelength shift optical fibers are arranged in the second direction. The first end of each transverse wavelength shift optical fiber is connected with the first photoelectric converter, that is, the transverse wavelength shift optical fiber and the first photoelectric converter are one-to-one corresponding, and the first end of the transverse wavelength shift optical fiber is connected to the corresponding first photoelectric converter. The first end of each longitudinal wavelength shift optical fiber is connected with the second photoelectric converter, that is, the longitudinal wavelength shift optical fiber and the second photoelectric converter are one-to-one corresponding, and the second end of the longitudinal wavelength shift optical fiber is connected to the corresponding second photoelectric converter. The second end of each transverse wavelength shift optical fiber and the second end of each longitudinal wavelength shift optical fiber are not connected to the photoelectric converter. When the cosmic muon passes through the first scintillator detector 11, the first scintillator plate 111 is excited, and the light signal generated by the de-excitation is transmitted to the first photoelectric converter through the light guide array plate 112 and the plurality of transverse wavelength shift optical fibers, and is transmitted to the second photoelectric converter through the light guide array plate 112 and the plurality of longitudinal wavelength shift optical fibers.

[0061] Further, the primordial muon spin polarization measurement system provided by the embodiment further comprises an electronic system, each first photoelectric converter and each second photoelectric converter is electrically connected with the electronic system, the light signals received by the first photoelectric converter and the second photoelectric converter are transmitted to the electronic system after conversion and reading, and finally the position and time of the primordial muon hitting the first scintillator detector 11 are reconstructed by analyzing the data converted into digital signals. Specifically, the position of the primordial muon when passing through the first scintillator detector 11 can be determined by the position of the transverse wavelength shift optical fiber receiving the light signal and the position of the longitudinal wavelength shift optical fiber receiving the light signal, and then the momentum direction and momentum size of the primordial muon can be obtained by the position and time of the primordial muon when passing through the two first scintillator detectors 11 arranged along the first direction.

[0062] Further, as shown in Figure 4 the first scintillator detector 1111 further comprises a first adapter 113 and a second adapter 114, the first adapter 113 is arranged on one side of the light guide array plate 112, the first photoelectric converter is arranged on the side of the first adapter 113 away from the light guide array plate 112, the transverse wavelength shift optical fiber is connected with the first photoelectric converter through the first adapter 113, and the second adapter 114 is arranged on the other side of the light guide array plate 112, the second photoelectric converter is arranged on the side of the second adapter 114 away from the light guide array plate 112, and the longitudinal wavelength shift optical fiber is connected with the second photoelectric converter through the second adapter 114. Because a large number of transverse wavelength shift optical fibers and a large number of longitudinal wavelength shift optical fibers are arranged in the light guide array plate 112, the first photoelectric converter corresponding to each transverse wavelength shift optical fiber and the second photoelectric converter corresponding to each longitudinal wavelength shift optical fiber are difficult to be directly installed on the light guide array plate 112 due to space limitation, and therefore the first adapter 113 and the second adapter 114 are arranged to provide sufficient space for the installation of the first photoelectric converter and the second photoelectric converter.

[0063] Optionally, as shown in Figure 5 the positron-electron detection unit 301 comprises a plurality of second scintillator detectors 3011, each second scintillator detector 3011 comprises a second scintillator plate and a third photoelectric converter, and the second scintillator plate is provided with the third photoelectric converter at both ends, and the plurality of second scintillator detectors 3011 of each positron-electron detection unit 301 are sequentially arranged along a direction perpendicular to the first direction.

[0064] Specifically, in the embodiment, as shown in Figures 1-3As shown, the first and second positron-electron detection unit groups 31 and 32 each include eight positron-electron detection units 301, each of which includes eight independently packaged second scintillator detectors 3011. Each second scintillator plate has a size of 15x135x175mm, and the gap between adjacent two second scintillator detectors 3011 is less than 0.5mm. Each second scintillator plate is independently packaged using a reflective film, an aluminum foil and an electrical tape to ensure that the ambient light signal outside the second scintillator plate does not cause false triggering of the third photoelectric converter. In addition to independent packaging, the eight second scintillator detectors 3011 in each positron-electron detection unit 301 are each provided with a large end cap at both ends. The geometry of the large end cap is specially designed to enclose the eight second scintillator detectors 3011 into a regular octagon with a side length of 132.51mm. Therefore, the azimuthal resolution of a single second scintillator detector 3011 is better than 6°. At the same time, in order to ensure the maintainability of the power supply of the positron-electron detection unit 301, an electronics module with centralized power supply and signal processing is provided in the large end cap. Therefore, only one power supply and eight signal outputs are required at one end of a positron-electron detection unit 301 to operate. The multi-channel readout electronics system framework provided by the positron-electron detection module 3 is as shown in Figure 13 As shown, the electrical signal generated by the scintillator in the system is processed by the front-end electronics signal processing, then transferred into the data acquisition hardware module through signal switching, and then the upper computer collects the data packet by sending control commands, and finally the preliminary analysis data can be output under the driving of the upper computer software module. We determine that it is a physical trigger if the two third photoelectric converters at both ends of a second scintillator detector 3011 trigger within a certain time range. Through the joint analysis between the signals of the cosmic muon momentum detection module 1 and the positron-electron detection module 3, the spatial distribution of the Michel electron generated by the cosmic muon can be reconstructed, and further the spin direction of the cosmic muon can be analyzed.

[0065] In the embodiment, as shown in Figure 2 and Figure 6 The cosmic muon stopping target 2 is cylindrical, the first and second positron-electron detection unit groups 31 and 32 each include eight positron-electron detection units 301, the eight positron-electron detection units 301 of the first positron-electron detection unit group 31 form a first detection space, the eight positron-electron detection units 301 of the second positron-electron detection unit group 32 form a second detection space, the first and second detection spaces are both regular octagonal prisms, and the central axes of the first and second detection spaces are both collinear with the axis of the cosmic muon stopping target 2. The diameter of the inscribed circle of the cross section of the first and second detection spaces perpendicular to the first direction is not less than the diameter of the cosmic muon stopping target 2.

[0066] Optionally, as shown in Figure 1 and Figure 2 , the present embodiment provides a muonium spin polarization measurement system, which further comprises a anticoincidence detection module 4, the anticoincidence detection module 4 is used for detecting muoniums which do not pass through the muonium momentum detection module 1 and reach the positron-electron detection module 3 or the muonium stopping target 2.

[0067] Further, as shown in Figure 1 , Figure 2 , Figure 7 and Figure 8 , the anticoincidence detection module 4 comprises a plurality of third scintillator detectors 41 which are arranged along the circumferential direction of the muonium stopping target 2 and surround the muonium stopping target 2, the third scintillator detectors 41 are arranged on the side of the positron-electron detection unit 301 which is far away from the muonium stopping target 2, and the third scintillator detectors 41 comprise third scintillator plates 411 and fourth photoelectric converters, and the two ends of each third scintillator plate 411 are provided with a fourth photoelectric converter. By shielding the gap between the first positron-electron detection unit group 31 and the second positron-electron detection unit group 32 through the third scintillator plates 411, when the rare transverse muonium passes through the third scintillator plates 411, the third scintillator plates 411 are excited, and the light signals generated when the third scintillator plates 411 are de-excited are received by the fourth photoelectric converters at the two ends of the third scintillator plates 411 and are converted and read out, and then are transmitted to the electronic system, so that the detection of the rare transverse muonium is realized. In the present embodiment, the anticoincidence detection module 4 comprises eight third scintillator detectors 41, the size of the third scintillator plate 411 is 320*300*30mm, and the detection efficiency of a single third scintillator detector 41 is higher than 97%.

[0068] Since the first positron-electron detection unit group 31 and the second positron-electron detection unit group 32 are arranged at intervals along the first direction, the rare transverse muoniums may pass through the gap between the first positron-electron detection unit group 31 and the second positron-electron detection unit group 32 and reach the muonium stopping target 2, and then decay on the muonium stopping target 2 to generate Michel electrons. The Michel electrons generated by the muoniums which do not pass through the muonium momentum detection module 1 and the positron-electron detection module 3 and reach the stopping target will interfere with the muonium spin polarization measurement, therefore, the present embodiment is provided with the anticoincidence detection module 4, the anticoincidence detection module 4 covers the solid angle between the first positron-electron detection unit group 31 and the second positron-electron detection unit group 32, detects the muoniums which pass through the gap between the first positron-electron detection unit group 31 and the second positron-electron detection unit group 32 and reach the muonium stopping target 2, and then removes the interference signals generated by the muoniums according to the detection information of the anticoincidence detection module 4.

[0069] In addition, the rare transverse primordial muons can not pass through the primordial muon momentum detection module 1, but directly pass through the two positron and electron detection units 301 of the positron and electron detection module 3, and do not pass through the primordial muon stopping target 2. For this case, the transverse primordial muon events can be screened out by coincidence between the respective third scintillator detectors 41 of the anticoincidence detection module 4, so that the interference signals generated by the transverse primordial muon events can be removed.

[0070] Optionally, as shown in Figure 1 and Figure 2 shown, the primordial muon spin polarization measurement system provided by the embodiment further includes a primordial muon energy reducer 6, which is arranged above the primordial muon momentum detection module 1 and is used to reduce the kinetic energy of the primordial muons passing through the primordial muon energy reducer 6.

[0071] Further, the primordial muon energy reducer 6 is a lead plate or a concrete plate, and the primordial muon energy reducer 6 is arranged perpendicularly to the first direction. After hitting the primordial muon energy reducer, the primordial muons interact with the atoms of the primordial muon energy reducer 6 and lose a large amount of kinetic energy, so that the primordial muons can stop on the primordial muon stopping target 2 after passing through the primordial muon energy reducer 6 and the primordial muon momentum detection module 1 to the primordial muon stopping target 2. By replacing the primordial muon energy reducer 6 and the primordial muon stopping target 2 with different thicknesses, the polarization properties of primordial muons with different energies can be measured.

[0072] In order to ensure that a sufficient number of primordial muons can stop on the stopping target after entering the primordial muon spin polarization measurement system, the primordial muon energy reducer 6 needs to have a large enough area. Specifically, the area of the primordial muon energy reducer 6 is at least 1m x 1m.

[0073] The primordial muon stopping target 2 is cast from a uniform material. In the present embodiment, the primordial muon stopping target 2 is made of copper. After passing through the primordial muon energy reducer 6, a considerable part of the primordial muons can hit the primordial muon stopping target 2, and finally a part of the primordial muons stop in the material of the primordial muon stopping target 2 after losing all kinetic energy through interaction in the primordial muon stopping target 2. Since the muon itself is an unstable particle, the primordial muons stopped in the primordial muon stopping target 2 will eventually decay and produce Michel electrons. The Michel electrons will be emitted outward from the primordial muon stopping target 2 and a part of them can hit the positron and electron detection module 3 and thus be detected by us.

[0074] Optionally, the first scintillator plate 111, the second scintillator plate and the third scintillator plate 411 are all plastic scintillators. The plastic scintillators are simple to make and low in price, easy to process into various shapes, high in transparency, good in light transmission performance, capable of being made into large-volume scintillators, stable in performance, short in scintillation decay time and suitable for nanosecond-level time measurement. The shapes and sizes of the first scintillator plate 111, the second scintillator plate and the third scintillator plate 411 can be freely selected as required, and the accuracy of the measurement result of the cosmic muon momentum detection module 1 can be ensured. The charged particles or photons can interact with the scintillator and deposit energy in the scintillator to push the electrons in the scintillator to the excited state. After the electrons are de-excited, the energy will propagate in the form of photons inside the scintillator. As long as a photoelectric converter is placed at a certain position of the scintillator, the light-emitting signal of the scintillator, that is, the signal of the charged particles hitting the scintillator, can be obtained. The first photoelectric converter, the second photoelectric converter, the third photoelectric converter and the fourth photoelectric converter in the embodiment all adopt silicon photomultiplier devices, that is, the silicon photomultiplier devices and the plastic scintillators are used to form the scintillator detector unit in the cosmic muon spin polarization measurement system. This type of detector only needs to be driven by a voltage lower than 100 V and can stably operate in various environments. For each plastic scintillator, independent packaging is adopted, so that each module can be individually disassembled for maintenance or upgrading.

[0075] Optionally, as shown in Figure 1 、 Figure 2 、 Figures 9-12 The cosmic muon spin polarization measurement system provided in the embodiment further includes a support module 5, and the cosmic muon momentum detection module 1, the cosmic muon stopping target 2, the positron and electron detection module 3 and the anti-coincidence detection module 4 are all arranged on the support module 5.

[0076] Specifically, as shown in Figure 1 、 Figure 2 、 Figures 9-12As shown, the support module 5 includes a support frame 51, a first support plate 52, a second support plate 53, a third support plate 54, and a support rod 55. The muon energy reducer 6 is arranged on the top of the support module 5, and is detachably connected with the support module 5. Different thicknesses of the muon energy reducer 6 can be replaced during use of the muon spin polarization measurement system. Specifically, the muon energy reducer 6 is connected with the support frame 51 by screws. The first support plate 52, the second support plate 53, and the third support plate 54 are arranged in a spaced manner along the height of the support frame 51 from top to bottom. The first pair of positron-electron detection units 31 are installed on the first support plate 52, the anticoincidence detection module 4 is installed on the second support plate 53, the second pair of positron-electron detection units 32 are installed on the third support plate 54, and the muon stopping target 2 is installed on the third support plate 54 through the support rod 55. Different sizes of the muon stopping target 2 can be replaced as needed. The muon momentum detection module 1 is installed on the support beam 511 at the upper part of the support frame 51, and the positions of the first scintillator detectors 11 on the beam can be adjusted along the support beam 511.

[0077] The working principle of the muon spin polarization measurement system provided by the embodiment is as follows:

[0078] The momentum of the muon is reduced by the muon energy reducer 6 arranged on the top of the muon spin polarization measurement system.

[0079] After passing through the muon energy reducer 6, the muon passes through the muon momentum detection module 1, and the muon momentum detection module 1 obtains the momentum information of the muon.

[0080] After passing through the muon momentum detection module 1, the muon reaches the muon stopping target 2 and decays on the stopping target.

[0081] The first pair of positron-electron detection units 31 and the second pair of positron-electron detection units 32 monitor the Michel electrons generated by the decay of the muon on the muon stopping target 2, and obtain the spatial distribution information of the Michel electrons generated by the decay of the muon.

[0082] The spin direction of the muon is reconstructed by using the spatial distribution information of the Michel electrons, and the spin polarization of the muon is reconstructed by combining the spin direction of the muon with the momentum direction of the muon when passing through the muon momentum detection module 1.

[0083] The muon spin polarization measurement system provided by the embodiment has the resolution ability of the momentum direction and size of the muon, and has the azimuthal angle resolution ability of the spatial distribution of the Michel electrons. The momentum of the muon and the spatial distribution of the Michel electrons can be independently measured. The noise can be reduced and the detection efficiency can be improved by coincidence measurement between multiple modules. The system is easy to customize, upgrade, and move and deploy.

[0084] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and replacements without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. A cosmogeneous muon spin polarization measurement system, characterized in that, include: The Cosmic Muon Momentum Detection Module (1) is used to detect the momentum information of Cosmic Muons passing through the Cosmic Muon Momentum Detection Module (1); A muon stopping target (2) is set below the muon momentum detection module (1) to stop some muons that have passed through the muon momentum detection module (1) on the muon stopping target (2). The axis of the muon stopping target (2) extends along a first direction, which is the height direction of the muon spin polarization measurement system. The positive and negative electron detection module (3) is located below the cosmoson momentum detection module (1). The positive and negative electron detection module (3) includes a first positive and negative electron detection unit group (31) and a second positive and negative electron detection unit group (32). The first positive and negative electron detection unit group (31), the cosmoson stopping target (2) and the second positive and negative electron detection unit group (32) are arranged at intervals along the first direction. The first positive and negative electron detection unit group (31) and the second positive and negative electron detection unit group (32) each include a plurality of positive and negative electron detection units (301) arranged circumferentially along the axis of the cosmoson stopping target (2). The positive and negative electron detection unit (301) is used to detect Michel electrons generated by the decay of cosmosons that stop on the cosmoson stopping target (2).

2. The cosmogeneous muon spin polarization measurement system according to claim 1, characterized in that, The cosmogenic muon momentum detection module (1) includes two first scintillator detectors (11), which are spaced apart along the first direction. The cosmogenic muon momentum detection module (1) is used to monitor the position and time when the cosmogenic muon passes through each of the first scintillator detectors (11).

3. The cosmogeneous muon spin polarization measurement system according to claim 2, characterized in that, The first scintillator detector (11) includes: The first scintillator plate (111) is arranged perpendicular to the first direction; A light guide array plate (112) covers the top surface of the first scintillator plate (111); Multiple transverse wavelength-shifting optical fibers are disposed within the optical guide array plate (112) and extend along a second direction, which is perpendicular to the first direction. The multiple transverse wavelength-shifting optical fibers are spaced apart along a third direction, and both the second direction and the first direction are perpendicular to the third direction. Multiple longitudinal wavelength-shifting optical fibers are provided, all of which are inserted into the optical guide array plate (112) and extend along a third direction. The multiple longitudinal wavelength-shifting optical fibers are spaced apart along the second direction. The first photoelectric converter is connected to the first end of each of the transverse wavelength shifting optical fibers. The second photoelectric converter is connected to the first end of each of the longitudinal wavelength shifting optical fibers.

4. The cosmogeneous muon spin polarization measurement system according to claim 3, characterized in that, The Yusheng Muon stopping target (2) is cylindrical.

5. The cosmogeneous muon spin polarization measurement system according to claim 3, characterized in that, The positive and negative electron detection unit (301) includes a plurality of second scintillator detectors (3011). The second scintillator detector (3011) includes a second scintillator plate and a third photoelectric converter. The third photoelectric converter is provided at both ends of the second scintillator plate. The plurality of second scintillator detectors (3011) of each positive and negative electron detection unit (301) are arranged sequentially along a direction perpendicular to the first direction.

6. The cosmogeneous muon spin polarization measurement system according to claim 5, characterized in that, It also includes an anti-coincidence detection module (4), which is used to detect cosmogens that arrive at the electron-positron detection module (3) or the cosmogen stopping target (2) without passing through the cosmogen momentum detection module (1).

7. The cosmogeneous muon spin polarization measurement system according to claim 6, characterized in that, The anti-coincidence detection module (4) includes a plurality of third scintillator detectors (41) arranged around the circumference of the cosmoson muon stopping target (2). The third scintillator detectors (41) are arranged on the side of the positive and negative electron detection unit (301) away from the cosmoson muon stopping target (2). The third scintillator detectors (41) include a third scintillator plate (411) and a fourth photoelectric converter. The fourth photoelectric converter is arranged at both ends of the third scintillator plate (411).

8. The cosmogeneous muon spin polarization measurement system according to claim 7, characterized in that, The first scintillator plate (111), the second scintillator plate, and the third scintillator plate (411) are all plastic scintillators.

9. The cosmogeneous muon spin polarization measurement system according to any one of claims 1-8, characterized in that, It also includes a cosmoson muon energy reducer (6), which is located above the cosmoson muon momentum detection module (1) and is used to reduce the kinetic energy of the cosmoson muons passing through the cosmoson muon energy reducer (6).

10. The cosmogeneous muon spin polarization measurement system according to claim 9, characterized in that, The Yusheng Muon energy reducer (6) is a lead plate or a concrete plate, and the Yusheng Muon energy reducer (6) is arranged perpendicular to the first direction.

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