Numerology 

Particle detectors. Elementary particle detector

Tens of thousands fly through our body every second. elementary particles from space - muons, electrons, neutrinos and so on. We do not feel and do not see them, but this does not mean that they do not exist. It doesn't mean they can't be fixed. We offer readers N+1 assemble a device with your own hands that will allow you to "see" this continuous cosmic rain.

"Real" particle detectors, such as those at the Large Hadron Collider, cost millions of dollars and weigh hundreds of tons, but we'll try to make do with a much more modest budget.

We will need:

  • dry ice (about 80 rubles per kilogram, it is advisable to buy a foam plastic thermal container for another 300 rubles - otherwise everything you bought will evaporate too quickly). A lot of dry ice is not needed, a kilogram is enough;
  • isopropyl alcohol (costs 370 rubles per 0.5 liter, sold in radio equipment stores);
  • a piece of felt (sewing shop, about 150 rubles);
  • glue to stick the felt to the bottom of the container (“Moment”, 150 rubles);
  • a transparent container, such as a plastic aquarium with a lid (we bought a hard plastic food container for 1.5 thousand rubles);
  • stand for dry ice, it can be a photographic cuvette (found in the editorial kitchen);
  • flashlight.

So let's get started. First you need to glue a piece of felt to the bottom of the container and wait a few hours for the glue to dry. After that, the felt must be soaked in isopropyl alcohol (make sure that alcohol does not get into your eyes!). It is desirable that the felt is completely saturated with alcohol, the remainder of which must then be drained. Then pour dry ice on the bottom of the cuvette, close the container with a lid and place it in dry ice with the lid down. Now you need to wait for the air inside the chamber to be saturated with alcohol vapor.

The principle of operation of the cloud chamber (aka "fog chamber") is that even a very weak impact causes the saturated vapor of alcohol to condense. As a result, even the impact of cosmic particles causes the vapor to condense, and chains of microscopic droplets - tracks - are formed in the chamber.

You can watch the experiment on our video:


A few notes from experience: you should not buy too much dry ice - it will evaporate completely in less than a day even in their thermal container, and you are unlikely to find an industrial refrigerator. It is necessary that the lid of the transparent container be black, for example, you can close it from below with black glass. Tracks will be better seen on a black background. You need to look exactly at the bottom of the container, where a characteristic fog is formed, similar to drizzling rain. It is in this fog that particle tracks appear.

What tracks can be seen:


Symmetry Magazine

These are not cosmic particles. Short and thick tracks are traces of alpha particles emitted by atoms of the radioactive gas radon, which continuously seeps from the bowels of the Earth (and accumulates in unventilated rooms).


Symmetry Magazine

Long narrow tracks are left by muons, the heavy (and short-lived) relatives of electrons. They are produced in abundance in the upper atmosphere when high-energy particles collide with atoms and create entire showers of particles, mostly muons.

In ch. XXIII we got acquainted with the devices used to detect microparticles - a cloud chamber, a scintillation counter, a gas-discharge counter. Although these detectors are used in elementary particle studies, they are not always convenient. The fact is that the most interesting processes of interaction, accompanied by mutual transformations of elementary particles, occur very rarely. A particle must meet a lot of nucleons or electrons on its way for an interesting collision to occur. In practice, it must go through a path measured in tens of centimeters - meters in dense matter (on such a path, a charged particle with an energy of billions of electron volts loses only part of its energy due to ionization).

However, in a cloud chamber or a gas-discharge counter, the sensitive layer (in terms of a dense substance) is extremely thin. In connection with this, some other methods for detecting particles have been applied.

The photographic method proved to be very fruitful. In special fine-grained photographic emulsions, each charged particle crossing the emulsion leaves a trace, which, after developing the plate, is detected under a microscope in the form of a chain of black grains. By the nature of the trace left by a particle in a photographic emulsion, one can determine the nature of this particle - its charge, mass, and energy. The photographic method is convenient not only because thick materials can be used, but also because in a photographic plate, in contrast to a cloud chamber, traces of charged particles do not disappear soon after the passage of the particle. When studying rare events, records may be exposed long time; this is especially useful in cosmic ray studies. Examples of rare events captured in photographic emulsion are shown above in Fig. 414, 415; Fig. is especially interesting. 418.

Another remarkable method is based on the use of the properties of superheated liquids (see Volume I, § 299). When a very pure liquid is heated to a temperature even slightly higher temperature boiling, the liquid does not boil, as surface tension prevents the formation of vapor bubbles. The American physicist Donald Glaeser (b. 1926) noted in 1952 that a superheated liquid instantly boils when irradiated sufficiently intensely; the additional energy released in the traces of fast electrons created in the liquid by -radiation provides the conditions for the formation of bubbles.

Based on this phenomenon, Glaeser developed the so-called liquid bubble chamber. Liquid at high blood pressure heated to a temperature close to, but less than, the boiling point. Then the pressure, and with it the boiling point, decrease, and the liquid is superheated. A trace of vapor bubbles is formed along the trajectory of a charged particle crossing the liquid at this moment. With the right lighting, it can be captured by a camera. As a rule, bubble chambers are located between the poles of a strong electromagnet, the magnetic field bends the particle trajectories. By measuring the length of the particle track, the radius of its curvature, and the density of bubbles, it is possible to establish the characteristics of the particle. Now bubble chambers have reached a high level of perfection; work, for example, chambers filled with liquid hydrogen, with a sensitive volume of several cubic meters. Examples of photographs of traces of particles in a bubble chamber are shown in fig. 416, 417, 419, 420.

Rice. 418. Transformations of particles recorded in a stack of photographic emulsions irradiated with cosmic rays. At a point, an invisible fast neutral particle caused the splitting of one of the emulsion nuclei and formed mesons (a "star" of 21 tracks). One of the mesons, the -meson, having traveled a path around (only the beginning and end of the trace are shown in the photograph; with the magnification used in the photograph, the length of the entire trace would have been ), stopped at a point and decayed according to the scheme . -meson, the trace of which is directed downward, was captured by the nucleus at the point, causing its splitting. One of the fragments of splitting was the nucleus, which, by means of decay, turned into a nucleus, instantly disintegrating into two particles flying in opposite directions - in the picture they form a “hammer”. -meson, having stopped, turned into -muon (and neutrino) (point). The end of the -muon trace is given in the right upper corner drawing; the trace of the positron formed during the decay is visible.

Rice. 419. Formation and decay of -hyperons. In a hydrogen bubble chamber in a magnetic field and irradiated with antiprotons, the reaction . It occurred at the end point of the trail (see diagram at the top of the figure). Neutral lambda and anti-lambda hyperons, having flown a short distance without the formation of a trace, decay according to the schemes. The antiproton annihilates with the proton, forming two and two -meson-quantum on the proton; proton does not visible trace, because in view of large mass does not receive sufficient energy when interacting with a -quantum

Elementary particle detector, ionizing radiation detector in experimental particle physics, a device designed to detect and measure the parameters of high-energy elementary particles, such as cosmic rays or particles produced in nuclear decays or in accelerators.

Main types [ | ]

Obsolete

Radiation protection detectors

Detectors for nuclear physics and elementary particle physics

  • Hodoscopic cameras
  • Counters
  • Track detectors
  • Mass analyzers

Detectors for colliding beam experiments[ | ]

In elementary particle physics, the term "detector" refers not only to various types of sensors for detecting particles, but also to large installations created on their basis and also including infrastructure to maintain their performance (cryogenic systems, air conditioning systems, power supplies), electronics for reading and primary data processing, auxiliary systems (for example, superconducting solenoids for creating inside the installation magnetic field). As a rule, such installations are now created by large international groups.

Since the construction of a large plant requires significant financial costs and human efforts, in most cases it is used not for one specific task, but for a whole range of various measurements. The main requirements for a modern detector for experiments at the accelerator are:

For specific tasks, additional requirements may be required, for example, for experiments measuring CP violation in a system of B mesons important role plays the coordinate resolution in the region of beam interaction.

Symbolic representation of a multilayer universal detector for a colliding beam accelerator.

The need to fulfill these conditions leads to a typical today's scheme of a universal multilayer detector. In the English-language literature, such a scheme is usually compared with an onion-like structure. In the direction from the center (beam interaction region) to the periphery, a typical detector for a colliding beam accelerator consists of the following systems:

track system[ | ]

The tracking system is designed to record the trajectory of the passage of a charged particle: coordinates of the interaction region, departure angles. In most detectors, the tracking system is placed in a magnetic field, which leads to a curvature of the trajectories of charged particles and makes it possible to determine their momentum and charge sign.

The track system is usually based on semiconductor or silicon detectors.

Identification system[ | ]

The identification system allows you to separate from each other Various types charged particles. The principle of operation of identification systems most often consists in measuring the velocity of a particle in one of three ways:

Together with the measurement of the momentum of a particle in a track system, this gives information about the mass and, consequently, about the type of the particle.

Calorimeter [ | ]

List of colliding beam accelerator detectors in operation or under construction[ | ]

Applications[ | ]

In addition to scientific experiments, elementary particle detectors are also used in applied tasks - in medicine (X-ray machines with a low dose of radiation,

As in any physical experiment, the study of elementary particles requires first put experiment and then register his results. The accelerator is engaged in setting up the experiment (collision of particles), and the results of collisions are studied using elementary particle detectors.

In order to reconstruct the picture of the collision, it is necessary not only to find out which particles were born, but also to measure their characteristics with great accuracy, primarily the trajectory, momentum, and energy. All this is measured using different types of detectors, which surround the place of particle collision in concentric layers.

Elementary particle detectors can be divided into two groups: track detectors, which measure the trajectory of the particles, and calorimeters that measure their energies. Track detectors try to follow the movement of particles without introducing any distortion. Calorimeters, on the other hand, must completely absorb a particle in order to measure its energy. As a result, a standard layout of a modern detector arises: inside there are several layers of track detectors, and outside - several layers of calorimeters, as well as special muon detectors. General form a typical modern detector is shown in fig. one.

The structure and principle of operation of the main components of modern detectors are briefly described below. The emphasis is on some of the most general principles detection. For specific detectors operating at the Large Hadron Collider, see Detectors at the LHC.

Track detectors

Track detectors reconstruct the trajectory of the particle. They are usually located in the region of the magnetic field, and then the particle's momentum can be determined from the curvature of the particle's trajectory.

The work of track detectors is based on the fact that a passing charged particle creates an ionization trail - that is, it knocks out electrons from atoms in its path. In this case, the ionization intensity depends both on the type of particle and on the material of the detector. Free electrons are collected by electronics, the signal from which reports the coordinates of the particles.

Vertex detector

summit(microvertex, pixel) detector- This is a multilayer semiconductor detector, consisting of separate thin plates with electronics deposited directly on them. This is the most the inner layer detectors: it usually begins immediately outside the vacuum tube (sometimes the first layer is mounted directly on the outer wall of the vacuum tube) and occupies the first few centimeters in the radial direction. As semiconductor material silicon is usually chosen because of its high radiation resistance (the inner layers of the detector are exposed to huge doses of hard radiation).

Essentially, the vertex detector works in the same way as a digital camera sensor. When a charged particle flies through this plate, it leaves a trace in it - an ionization cloud several tens of microns in size. This ionization is read by the electronic element directly below the pixel. By knowing the coordinates of the intersection points of a particle with several consecutive pixel detector plates, it is possible to reconstruct the three-dimensional trajectories of the particles and trace them back inside the pipe. Through the intersection of such reconstructed trajectories at some point in space, vertex- the point at which these particles were born.

Sometimes it turns out that there are several such vertices, and one of them usually lies directly on the axis of collision of colliding beams (primary vertex), and the second one is at a distance. This usually means that protons collided at the primary vertex and immediately gave rise to several particles, but some of them managed to fly some distance before decaying into child particles.

In modern detectors, the vertex reconstruction accuracy reaches 10 microns. This makes it possible to reliably register cases when the secondary vertices are 100 microns away from the collision axis. It is precisely at such distances that various metastable hadrons fly off, which have a c- or b-quark in their composition (the so-called "enchanted" and "charming" hadrons). Therefore, the vertex detector is the most important tool of the LHCb detector, main task which will just be the study of these hadrons.

Semiconductors work on a similar principle. microstrip detectors, in which the thinnest, but rather long stripes are used instead of small pixels sensitive material. In them, ionization does not settle immediately, but shifts along the strip and is read at its end. The strips are designed in such a way that the speed of the charge cloud displacement along it is constant and that it does not blur. Therefore, knowing the moment when the charge arrives at the reading element, it is possible to calculate the coordinates of the point where the charged particle pierced the strip. The spatial resolution of microstrip detectors is worse than that of pixel detectors, but they can cover much more about large area, since they do not require such a large number reading elements.

Drift cameras

Drift cameras- These are gas-filled chambers that are placed outside the semiconductor track detectors, where the radiation level is relatively low and such a high accuracy of position determination is not required, as with semiconductor detectors.

A classic drift chamber is a tube filled with gas, inside which many very thin wires are stretched. It works like a vertex detector, but not on a flat plate, but in volume. All wires are under tension, and their arrangement is chosen in such a way that a uniform electric field. When a charged particle flies through a gas chamber, it leaves a spatial ionization trail. Under the action of an electric field, ionization (first of all, electrons) moves at a constant speed (physicists say “drifts”) along the field lines towards the anode wires. Having reached the edge of the chamber, the ionization is immediately absorbed by the electronics, which transmits a signal pulse to the output. Since there are a lot of reading elements, the signals from them can be used to restore the coordinates of a passing particle, and hence the trajectory, with good accuracy.

Usually, the amount of ionization that a passing particle creates in a gas chamber is small. In order to increase the reliability of charge collection and registration and reduce the error in its measurement, it is necessary to amplify the signal even before it is registered by the electronics. This is done using a special network of anode and cathode wires stretched near the reading equipment. Passing near the anode wire, the electron cloud generates an avalanche on it, as a result of which the electronic signal is multiplied.

The stronger the magnetic field and the larger the dimensions of the detector itself, the stronger the particle trajectory deviates from a straight line, which means that the more reliably it is possible to measure its curvature radius and reconstruct the particle momentum from this. Therefore, to study reactions with particles of very high energies, hundreds of GeV and TeV, it is desirable to build larger detectors and use stronger magnetic fields. For purely engineering reasons, it is usually possible to increase only one of these values ​​at the expense of the other. The two largest detectors at the LHC - ATLAS and CMS - just differ in which of these values ​​is optimized. At the ATLAS detector larger sizes, but smaller field, while in the CMS detector stronger field, but overall it is more compact.

Time projection camera

A special type of drift chamber is the so-called time projection camera(VPK). In fact, the VPK is one large, several meters in size, cylindrical drift cell. In its entire volume, a uniform electric field is created along the axis of the cylinder. The entire swirling ionization trail, which particles leave when flying through this chamber, drifts uniformly to the ends of the cylinder, retaining its spatial shape. The trajectories are, as it were, “projected” onto the ends of the chamber, where a large array of reading elements registers the arrival of the charge. The radial and angular coordinates are determined by the sensor number, and the coordinate along the cylinder axis is determined by the time of signal arrival. Thanks to this, it is possible to restore a three-dimensional picture of the movement of particles.

Among the experiments running at the LHC, the ALICE detector uses the time-projection camera.

Roman Pots detectors

There is a special type of semiconductor pixel detectors that work directly inside the vacuum tube, in close proximity to the beam. First introduced in the 1970s research group from Rome, and they have since been given the name Roman pots("Roman pots").

Roman Pots detectors have been designed to detect particles deviated by very small angles during a collision. Conventional detectors located outside the vacuum tube are unsuitable here simply because a particle emitted at a very small angle can fly for many kilometers inside the vacuum tube, turning along with the main beam and not escaping. In order to register such particles, it is necessary to place small detectors inside the vacuum tube across the beam axis, but without touching the beam itself.

To do this, at a certain section of the accelerating ring, usually at a distance of hundreds of meters from the point of collision of colliding beams, a special section of a vacuum tube with transverse "sleeves" is inserted. Small, several centimeters in size, pixel detectors are placed in them on mobile platforms. When the beam is just injected, it is still unstable and has large transverse oscillations. The detectors at this time are hidden inside the sleeves in order to avoid damage from a direct beam hit. After the beam stabilizes, the platforms move out of their arms and move the sensitive matrices of the Roman Pots detectors in close proximity to the beam, at a distance of 1-2 millimeters. At the end of the next accelerator cycle, before discarding the old beam and injecting a new one, the detectors are drawn back into their arms and wait for the next session of operation.

The pixel detectors used in Roman Pots differ from conventional vertex detectors in that they maximize the portion of the wafer surface occupied by the sensitive elements. In particular, on the edge of the plate, which is closest to the beam, there is practically no insensitive "dead" zone ( "edgeless"-technology).

One of the experiments at the Large Hadron Collider, TOTEM, will just use several of these detectors. Several more similar projects are under development. The vertex detector of the LHCb experiment also carries some elements of this technology.

You can read more about these detectors in the CERN Courier article Roman pots for the LHC or in the technical documentation of the TOTEM experiment.

Calorimeters

Calorimeters measure the energy of elementary particles. To do this, a thick layer of a dense substance (usually heavy metal- lead, iron, brass). A particle in it collides with electrons or atomic nuclei and as a result generates a stream of secondary particles - shower. The energy of the initial particle is distributed among all shower particles, so that the energy of each individual particle in this shower becomes small. As a result, the shower gets stuck in the thickness of the substance, its particles are absorbed and annihilated, and some, quite definite, fraction of the energy is released in the form of light. This flash of light is collected at the ends of the calorimeter by photomultipliers, which convert it into an electrical impulse. In addition, the shower energy can be measured by collecting ionization with sensitive plates.

Electrons and photons, passing through matter, collide mainly with the electron shells of atoms and generate an electromagnetic shower - a stream of a large number of electrons, positrons and photons. Such showers develop rapidly at shallow depths and are usually absorbed in a layer of matter several tens of centimeters thick. High-energy hadrons (protons, neutrons, pi-mesons and K-mesons) lose energy mainly due to collisions with nuclei. In this case, a hadron shower is generated, which penetrates much deeper into the thickness of matter than an electromagnetic one, and besides, it is wider. Therefore, in order to completely absorb a hadronic shower from a particle of very high energy, one or two meters of matter are required.

The difference between the characteristics of electromagnetic and hadron showers is used to the maximum in modern detectors. Calorimeters are often made two-layer: inside are located electromagnetic calorimeters, in which predominantly electromagnetic showers are absorbed, and outside - hadron calorimeters, which are "reached" only by hadron showers. Thus, calorimeters not only measure energy, but also determine the "type of energy" - whether it is of electromagnetic or hadronic origin. This is very important for a correct understanding of what happened in the center of the proton collision detector.

To register a shower by optical means, the material of the calorimeter must have scintillation properties. AT scintillator photons of one wavelength are absorbed very efficiently, leading to the excitation of the molecules of the substance, and this excitation is removed by emitting photons of lower energy. For the emitted photons, the scintillator is already transparent, and therefore they can reach the edge of the calorimetric cell. Calorimeters use standard, long-studied scintillators, for which it is well known what part of the energy of the initial particle is converted into an optical flash.

To effectively absorb showers, it is necessary to use as dense a substance as possible. There are two ways to reconcile this requirement with the requirements for scintillators. First, one can choose very heavy scintillators and fill the calorimeter with them. Secondly, it is possible to make a "puff" of alternating plates of a heavy substance and a light scintillator. There are also more exotic versions of the calorimeter design, for example, "spaghetti" calorimeters, in which many thin quartz fibers are embedded in a matrix of a massive absorber. A shower, developing along such a calorimeter, creates Cherenkov light in the quartz, which is output through the fibers to the end of the calorimeter.

The accuracy of restoring the energy of a particle in a calorimeter improves with increasing energy. For particles with energies of hundreds of GeV, the error is about a percent for electromagnetic calorimeters and a few percent for hadronic ones.

Muon chambers

A characteristic feature of muons is that they lose energy very slowly as they move through matter. This is due to the fact that, on the one hand, they are very heavy, therefore they cannot effectively transfer energy to electrons in a collision, and secondly, they do not participate in strong interaction, therefore they are weakly scattered by nuclei. As a result, muons can fly many meters of matter before they stop, penetrating where no other particles can reach.

This, on the one hand, makes it impossible to measure the energy of muons using calorimeters (after all, a muon cannot be completely absorbed), but on the other hand, it makes it possible to distinguish muons from other particles well. In modern detectors muon chambers located in the outermost layers of the detector, often even outside the massive metal yoke that creates a magnetic field in the detector. Such tubes measure not the energy, but the momentum of muons, and at the same time it can be assumed with good certainty that these particles are precisely muons, and not anything else. There are several varieties of muon chambers used for different purposes.

Particle identification

A separate issue is particle identification, that is, finding out what kind of particle flew through the detector. This would not be difficult if we knew the mass of the particle, but it is precisely this that we usually do not know. On the one hand, the mass can in principle be calculated using the formulas of relativistic kinematics, knowing the energy and momentum of the particle, but, unfortunately, the errors in their measurement are usually so large that they do not allow distinguishing, for example, a pi-meson from a muon due to their proximity wt.

In this situation, there are four main methods for identifying particles:

  • By response in different types calorimeters and muon tubes.
  • By energy release in track detectors. different particles produce different amount ionization per centimeter of path, and it can be measured by the signal strength from track detectors.
  • Via Cherenkov counters. If a particle flies through a transparent material with a refractive index n at a speed greater than the speed of light in that material (that is, greater than c/n), then it emits Cherenkov radiation in strictly defined directions. If we take airgel as the detector substance (the typical refractive index n= 1.03), then the Cherenkov radiation from particles moving at a speed of 0.99 c and 0.995 c, will differ significantly.
  • Via time-of-flight cameras. In them, with the help of detectors with a very high temporal resolution, the time of flight of a particle in a certain section of the chamber is measured and its speed is calculated from this.

Each of these methods has its own difficulties and errors, so particle identification is usually not guaranteed to be correct. Sometimes a program for processing "raw" data from a detector can come to the conclusion that a muon flew through the detector, although in fact it was a pion. It is impossible to get rid of such errors completely. It remains only to carefully study the detector before operation (for example, using cosmic muons), find out the percentage of cases of incorrect identification of particles, and always take it into account when processing real data.

Requirements for detectors

Modern particle detectors are sometimes referred to as "big brothers" digital cameras. However, it is worth remembering that the operating conditions of the camera and the detector are fundamentally different.

First of all, all elements of the detector must be very fast and very precisely synchronized with each other. At the Large Hadron Collider, at peak performance, the bunches will collide 40 million times per second. In each collision, the birth of particles will occur, which will leave their “picture” in the detector, and the detector must not “choke” on this stream of “images”. As a result, in 25 nanoseconds, it is required to collect all the ionization left by flying particles, turn it into electrical signals, and clean the detector, preparing it for the next portion of particles. In 25 nanoseconds, particles fly only 7.5 meters, which is comparable to the size of large detectors. While ionization from passing particles is gathering in the outer layers of the detector, particles from the next collision are already flying through its inner layers!

Second key requirement to the detector radiation resistance. Elementary particles flying away from the place of collision of bunches are real radiation, and very hard. For example, the expected absorbed dose of ionizing radiation that the vertex detector will receive during operation is 300 kilogray plus a total neutron flux of 5·10 14 neutrons per cm 2 . Under these conditions, the detector should work for years and still remain serviceable. This applies not only to the materials of the detector itself, but also to the electronics with which it is stuffed. It took several years to create and test fault-tolerant electronics that will work in such harsh radiation conditions.

Another requirement for electronics - low power output. Inside multi-meter detectors there is no free space - every cubic centimeter of volume is filled with useful equipment. The cooling system inevitably takes away the working volume of the detector - after all, if a particle flies right through the cooling tube, it simply will not be registered. Therefore, the energy release from the electronics (hundreds of thousands of separate boards and wires that take information from all components of the detector) should be minimal.

Additional literature:

  • K. Groupen. "Elementary particle detectors" // Siberian Chronograph, Novosibirsk, 1999.
  • Particle Detectors (PDF, 1.8 Mb).
  • Particle detectors // chapter from study guide B. S. Ishkhanov, I. M. Kapitonov, E. I. Kabin. “Particles and Nuclei. Experiment". M.: Publishing house of Moscow State University, 2005.
  • N. M. Nikityuk. Precision microapex detectors (PDF, 2.9 Mb) // ECHAYA, vol. 28, no. 1, pp. 191–242 (1997).

Radiation protection detectors

Detectors for nuclear physics and elementary particle physics

  • Cherenkov radiation detector
  • Gas ionization detector

Detectors for colliding beam experiments

In elementary particle physics, the term "detector" refers not only to various types of sensors for detecting particles, but also to large installations created on their basis and also including infrastructure to maintain their performance (cryogenic systems, air conditioning systems, power supplies), electronics for reading and primary data processing, auxiliary systems (for example, superconducting solenoids for creating a magnetic field inside the installation). As a rule, such installations are now created by large international groups.

Since the construction of a large installation requires significant financial and human effort, in most cases it is used not for one specific task, but for a whole range of different measurements. The main requirements for a modern detector for experiments at the accelerator are:

  • High efficiency (low percentage of lost particles or particles with poorly defined parameters)
  • Ability to separate different types of particles produced in decay (pions, kaons, protons, etc.)
  • The ability to accurately measure the momentum of charged particles to reconstruct the invariant mass of unstable states.
  • The ability to accurately measure photon energy.

For specific tasks, additional requirements may be required, for example, for experiments measuring CP violation in a system of B mesons, an important role is played by the coordinate resolution in the region of beam interaction.

The need to fulfill these conditions leads to a typical today's scheme of a universal multilayer detector. In the English-language literature, such a scheme is usually compared with an onion-like structure. In the direction from the center (beam interaction region) to the periphery, a typical detector for a colliding beam accelerator consists of the following systems:

track system

The tracking system is designed to record the trajectory of the passage of a charged particle: coordinates of the interaction region, departure angles. In most detectors, the tracking system is placed in a magnetic field, which leads to a curvature of the trajectories of charged particles and makes it possible to determine their momentum and charge sign.

The track system is usually based on gas ionization detectors or semiconductor silicon detectors.

Identification system

The identification system allows different types of charged particles to be separated from each other. The principle of operation of identification systems most often consists in measuring the velocity of a particle in one of three ways:

  • by the angle of radiation of Cherenkov light in a special radiator (as well as by the very fact of the presence or absence of Cherenkov radiation),
  • by time of flight to the registration point,
  • by the specific ionization density of the substance.

Together with the measurement of the momentum of a particle in a track system, this gives information about the mass and, consequently, about the type of the particle.

Calorimeter

List of colliding beam accelerator detectors in operation or under construction

  • Detectors at the LHC Collider (CERN)
  • Detectors at the Tevatron collider
  • Detectors at electron-positron colliders
    • BaBar (PEP-II Collider, SLAC)
    • Belle (collider KEKB, KEK)
    • BES (BEPC Collider, Beijing)
    • CLEO (CESR Collider)
    • KEDR (collider VEPP-4, Novosibirsk)
    • KMD, SND (collider VEPP-2M, VEPP-2000, Novosibirsk)

Applications

In addition to scientific experiments, elementary particle detectors are also used in applied tasks - in medicine (X-ray machines with a low dose of radiation, tomographs, radiation therapy), materials science (defectoscopy), for pre-flight screening of passengers and baggage at airports.

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Literature

  • K. Groupen. Detectors of elementary particles. Novosibirsk. Siberian Chronograph, 1999.
  • Groupen, C.(June 28-July 10 1999). "Physics of Particle Detection". AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII 536 : 3–34, Istanbul: Dordrecht, D. Reidel Publishing Co.. DOI:.
  • Semiconductor detectors in dosimetry ionizing radiation/ V. K. Lyapidevsky .. - M .: Atomizdat, 1973. - 179 p.
  • Nikolaev, V. A. Solid-state track detectors in radiation research / Nikolaev, V.A. - St. Petersburg. : Polytechnic Publishing House. un-ta, 2012. - 284 p. - ISBN 978-5-7422-3530-9.
  • Proportional and drift chambers / International meeting on the technique of wire chambers (June 17 - 20, 1975; Dubna) .. - Template: Dubna: Publishing House of the Association. inst. I. issled., 1975. - 344 p. - ISBN 978-5-7422-3530-9.
  • Akimov, Yu. K. Gas detectors of nuclear radiation. - Template:Dubna. : JINR, 2011. - 243 p. - ISBN 978-5-9530-0272-1.

An excerpt characterizing the Elementary Particle Detector

“Such a strange antipathy,” thought Pierre, “and before that I even liked him very much.
In the eyes of the world, Pierre was a great gentleman, a somewhat blind and funny husband. famous wife, a smart eccentric, doing nothing, but not harming anyone, a nice and kind fellow. In the soul of Pierre, during all this time, complex and difficult work took place. internal development which revealed much to him and led him to many spiritual doubts and joys.

He continued his diary, and this is what he wrote in it during this time:
“November 24th.
“I got up at eight o’clock, read Holy Scripture, then went to the office (Pierre, on the advice of a benefactor, entered the service of one of the committees), returned to dinner, dined alone (the countess has many guests, unpleasant to me), ate and drank moderately and after dinner he copied plays for the brothers. In the evening he went down to the countess and told a funny story about B., and only then remembered that he should not have done this, when everyone was already laughing out loud.
“I go to bed with a happy and peaceful spirit. Great Lord, help me to walk in Your paths, 1) overcome the part of anger - by quietness, slowness, 2) lust - by abstinence and disgust, 3) move away from the hustle and bustle, but do not excommunicate myself from a) state affairs of service, b) from family worries , c) from friendly relations and d) economic pursuits.
“November 27th.
“I got up late and woke up for a long time lying on the bed, indulging in laziness. My God! help me and strengthen me so that I may walk in Your ways. I read Holy Scripture, but without the proper feeling. Brother Urusov came and talked about the vanities of the world. He spoke about the new plans of the sovereign. I began to condemn, but I remembered my rules and the words of our benefactor that a true Freemason should be an assiduous worker in the state when his participation is required, and a calm contemplator of what he is not called to. My tongue is my enemy. Brothers G. V. and O. visited me, there was a preparatory conversation for the acceptance of a new brother. They make me the speaker. I feel weak and unworthy. Then the discussion turned to the explanation of the seven pillars and steps of the temple. 7 sciences, 7 virtues, 7 vices, 7 gifts of the Holy Spirit. Brother O. was very eloquent. In the evening, the acceptance took place. The new arrangement of the premises greatly contributed to the splendor of the spectacle. Boris Drubetskoy was accepted. I proposed it, I was the rhetorician. A strange feeling agitated me throughout my stay with him in the dark temple. I found in myself a feeling of hatred for him, which I vainly strive to overcome. And therefore I would have wished to truly save him from evil and lead him on the path of truth, but bad thoughts about him did not leave me. It seemed to me that his purpose in joining the fraternity was only a desire to get close to people, to be in favor with those in our lodge. Except for the reasons that he asked several times if N. and S. were in our box (to which I could not answer him), except that, according to my observations, he is not able to feel respect for our holy Order and is too busy and satisfied outer man to wish for spiritual improvement, I had no reason to doubt it; but he seemed insincere to me, and all the time when I stood with him eye to eye in the dark temple, it seemed to me that he smiled contemptuously at my words, and I really wanted to prick his bare chest with the sword that I held, put to it . I could not be eloquent and could not sincerely convey my doubt to the brothers and the great master. Great architecton of nature, help me find true ways leading out of the labyrinth of lies.
After that, three sheets were omitted from the diary, and then the following was written:
“I had an instructive and long conversation alone with brother B, who advised me to stick to brother A. Much, although unworthy, was revealed to me. Adonai is the name of the creator of the world. Elohim is the name of the ruler of all. The third name, the name of the utterance, having the meaning of the All. Conversations with Brother V. reinforce, refresh, and establish me on the path of virtue. With him there is no room for doubt. It is clear to me the difference between the poor teaching of the social sciences and our holy, all-embracing teaching. Human sciences subdivide everything - in order to understand, they kill everything - in order to consider. In the holy science of the Order, everything is one, everything is known in its totality and life. Trinity - the three principles of things - sulfur, mercury and salt. Sulfur of unctuous and fiery properties; in conjunction with salt, its fieryness arouses hunger in it, by means of which it attracts mercury, seizes it, holds it, and collectively produces separate bodies. Mercury is a liquid and volatile spiritual essence - Christ, the Holy Spirit, He.
“December 3rd.
“Woke up late, read the Holy Scriptures, but was insensible. Then he got out and walked around the room. I wanted to think, but instead my imagination presented an incident that happened four years ago. Mr. Dolokhov, after my duel, meeting with me in Moscow, told me that he hoped that I was now using full peace of mind despite the absence of my wife. I didn't answer then. Now I recalled all the details of this meeting, and in my soul spoke to him the most spiteful words and sharp replies. He came to his senses and gave up this thought only when he saw himself inflamed with anger; but did not repent of it enough. After that, Boris Drubetskoy came and began to tell various adventures; but from the very moment of his arrival I became dissatisfied with his visit and told him something nasty. He objected. I flared up and said a lot of unpleasant and even rude things to him. He fell silent and I caught myself only when it was already too late. My God, I can't deal with him at all. This is due to my ego. I put myself above him and therefore become much worse than him, for he is indulgent towards my rudeness, and on the contrary, I have contempt for him. My God, grant me in his presence to see more of my abomination and act in such a way that it would be useful to him. After dinner I fell asleep, and while I was falling asleep, I distinctly heard a voice saying in my left ear: “Your day.”
“I saw in a dream that I was walking in the dark, and suddenly surrounded by dogs, but I was walking without fear; suddenly one small one grabbed me by the left stegono with her teeth and did not let go. I started pushing her with my hands. And as soon as I tore it off, another, even larger one, began to gnaw at me. I began to lift it and the more I lifted it, the bigger and heavier it became. And suddenly brother A. came and, taking me by the arm, led me with him and led me to the building, to enter which I had to go along a narrow plank. I stepped on it and the board buckled and fell, and I began to climb the fence, which I could hardly reach with my hands. After a lot of effort, I dragged my body so that my legs hung on one side and my torso on the other side. I looked around and saw that Brother A. was standing on the fence and was pointing me to a large avenue and a garden, and a large and beautiful building in the garden. I woke up. Lord, Great Architecton of nature! help me tear off the dogs from me - my passions and the last of them, integrating the strength of all the former ones, and help me enter that temple of virtue, which I have achieved in a dream.
“December 7th.
“I had a dream that Iosif Alekseevich was sitting in my house, I am very happy, and I want to treat him. It’s as if I’m chatting with strangers incessantly and suddenly remembered that he can’t like it, and I want to get closer to him and hug him. But as soon as I approached, I see that his face has changed, it has become young, and he quietly says something to me from the teachings of the Order, so quietly that I cannot hear. Then, as if, we all left the room, and something strange happened here. We sat or lay on the floor. He told me something. And it was as if I wanted to show him my sensitivity, and without listening to his speech, I began to imagine the state of my inner man and the grace of God that overshadowed me. And there were tears in my eyes, and I was pleased that he noticed it. But he looked at me with annoyance and jumped up, cutting off his conversation. I became embittered and asked if what had been said referred to me; but he did not answer, showed me an affectionate look, and after that we suddenly found ourselves in my bedroom, where there is a double bed. He lay down on her on the edge, and I seemed to burn with a desire to caress him and lie down right there. And he seemed to ask me: “Tell me, what is your main passion? Did you recognize him? I think you already know him." I, embarrassed by this question, answered that laziness was my main addiction. He shook his head in disbelief. And I answered him, even more embarrassed, that although I live with my wife, according to his advice, but not as the husband of my wife. To this he objected that he should not deprive his wife of his affection, he made me feel that this was my duty. But I answered that I was ashamed of it, and suddenly everything disappeared. And I woke up and found in my thoughts the text of the Holy Scriptures: The belly was the light of a man, and the light shines in the darkness and the darkness does not embrace it. Iosif Alekseevich's face was youthful and bright. On this day I received a letter from a benefactor in which he writes about the obligations of marriage.