Antiproton (English: antiproton), particle type isComposite particleIs the antiparticle of the proton, its mass andspinIt is the same as the proton and has the same lifetime as the proton, but its charge andmagnetic momentIn contrast to the proton, it has the same negative charge as the electron.When it meets the proton, it will annihilate and be converted into energy.
Quality andspinSame as proton, but with charge andmagnetic momentIn contrast to the proton, it has the same negative charge as the electron.The lifetime is also comparable to that of protons.An antiproton is composed of two upper anti quarks and one lower anti quark.Although the antiproton itself is stable, it cannot be preserved in the general natural environment because the antiproton will annihilate when it contacts the proton and convert it into energy.
Discovery process
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Dirac predicted the existence of antiparticles as early as 1928.EachparticleIt has one quality, life spanspinStrictly equal, but the charge is exactly oppositeAntiparticleExists.
On August 2, 1932,California Institute of TechnologyAnderson and others solemnly announced to the world that they had foundpositron。The discovery of positrons confirmed Dirac's antiparticle theory, someTheoretical physicistWe began to take this theory seriously.1934PauliAnd Kraft proved that even if a stable negative energy particle sea could not be formed, there would be corresponding antiparticles.So people began to look for antiparticles of other particles.
In 1954University Of California OfLawrence Radiation Laboratory6.4 billion yuanElectron voltThis provides conditions for finding antiprotons.In 1955, Chamberlain and Segory confirmed the existence of antiprotons observed the previous year with the above accelerators.Since antiprotons have very few opportunities, only a small number of antiprotons can be generated every 100 billion high-energy proton collisions, so it is extremely difficult to confirm the existence of antiprotons.In 1955, their experimental group measured 60 antiprotons.As the probability of accidental coincidence is low, the numeration system is not good, but it is more reliable.
Soon they found the existence of antineutrons, althoughHigh-energy particleAntineutrons can also be generated when shooting, but because the antineutron is not charged, it is more difficult to identify it from other particles.They use antiprotons andNucleusTo give or obtain its negative charge from a protonpositive chargeIn this way, protons become neutrons and antiprotons becomeAntineutron。
Antiproton nuclear interaction
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The research on various phenomena after antiproton collision with atomic nucleus is in the preliminary stage, which is a kind of reaction expected to obtain the existence of antiproton bound states or resonance states in the nucleus.Theoretically, it is speculated that if there is an antiproton bound state in the nucleus, because the mean field is deep well and absorption type, the binding energy of low energy level will be very large and the energy level width will be very wide, such as dozens of Mev, making the energy level difficult to distinguish.The experimental results, because the background of quasi free knockout reaction and statistical evaporation must be deducted, are not enough to explain the existence of antiproton bound states in the nucleus, but there is no negative evidence.
Recently, due to the discovery of the example with jie quark in the painting, people are very interested in finding the nuclear bound state with poly in the nucleus, which requires the antiproton beam at high energy.Some estimates have been made of the possibility of the existence of civilian particles in the nucleus.Since it is not subject to the blocking effect of incompatibility in bubbles, and its existence is purely due to the gluon exchange force, it is likely to exist in the Hua H3 system.Its binding energy is about 19 Mev.
Antiproton storage ring device
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In 1983, the Western European Nuclear Research Center (cERN) built the anti proton storage ring device LEAR.It is an antiproton beam device that can obtain high current and high resolution, so that the study of antiproton physics enters a new stage. It is not only used to study various processes that occur after antiproton and nucleon collision, but also used to study baryonium, proton dipole and namely scattering phenomena, their resonance and bound states, and various particles generated after adding annihilation,And because its resolution is less than the energy level distance of the atomic nucleus, the antiproton andNucleusThe process of scattering into different final state channels can be distinguished, such as elastic channels and inelastic channels that determine the final state.[1]
History of Antiproton Science
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Cosmic ray experts had hoped that antiprotons would fall into their net like positrons, but the fact proved that the antimatter nature of nuclei was more elusive.In Dirac's words, the radiation quantum must have enough energy to dig out a particle from the negative energy state "sea".By 1947, this view had been clearly quantified as: the quantum of radiation must be transformed into a particle antiparticle pair.To achieve this conversion, the radiation quantum must provide twice the mass of a single particle or antiparticle.The cosmic ray quantum discovered at that time can only form the mass of two electrons, but to form a proton antiproton pair, it must have 2000 times the energy of the above cosmic ray quantum radiation.In 1954 and 1955, there were some vague cosmic ray reports on the elusive antiprotons, but these results were not convincing.
In 1954, the high-energy proton synchronous phase stabilized accelerator, the most powerful atom smasher in the world at that time, began to operate in Berkeley.In 1955, Chamberlain, Segre, C. Wie gand and T. YsPilanist began to prepare to use the accelerator to capture antiprotons.They hope that the accelerator can accelerate charged particles to their design energy value to cross the barrier of antiproton.But Anderson's pioneering experiment shows that it is very difficult to distinguish between positrons moving in one direction and electrons moving in the other direction.Only one of every 1 million protons produced by the new accelerator can produce antiprotons, and the rest will become other particles.In order to extract the precious antiproton essence, they used a dual magnetic lens system to make the particle beam more pure.Just as a prism can divide a beam of white light into its various colored lights, the purpose of the system is to separate the mixed particle beams according to their different energies when passing through the magnetic field.Just as Anderson used to distinguish between fast positrons and slow positrons by bending the track in the magnetic field, the experiment used a magnet to sweep the positively charged particles and filter out the most promising beam of negatively charged particles rich in antiprotons.In order to identify antiprotons, the time of particles passing through two magnetic lenses 12 meters apart was measured experimentally.Most of the subnuclear particles produced by the new accelerator move at the speed of light, and it takes 40 nanoseconds to travel 12 meters.Because the antiproton is very heavy, it moves slowly, taking 51 nanoseconds.Although nothing can travel faster than the speed of light in vacuum, high-energy particles can pass through transparent objects like glass at a speed faster than the speed of light in glass and generate Cherenkov light, whose direction depends on the speed of high-energy particles.They designed an ingenious speed filter, which uses a cylindrical mirror to ensure that only the light corresponding to the antiproton is reflected to its focus, and is picked up by an optical amplifier.
In 1955, the energy of the accelerator reached the stop value of the antiproton, making it possible to detect antiprotons.In order to detect the antiproton, they set the electronic circuit of the detection system to "start" 51 nanoseconds after the accelerator energy reached the threshold, and the Cherenkov optical amplifier recorded the optical signal.After the experiment began, the four experimenters watched the oscilloscope anxiously.At first, nothing happened.They thought that something wrong might have affected the delicate equipment, so they turned the magnetic field of the magnetic prism, which made the instrument very sensitive to a large number of positively charged protons and could easily get the signal of protons.However, they still did not get the proton count.So they checked the calculation and found that there was an incorrect setting in the magnetic prism.After correction, they started from the detection of protons. After seeing a large number of proton counts, they turned the magnetic field back to detect antiprotons.Soon, the first antiproton counting appeared.The experiment continued for three months, and further experimental results showed that the mass of proton and antiproton was equal within an error of about 5%.In this way, those who bet against the existence of antiprotons had to throw in the towel.Once the antiproton is discovered, it immediately becomes the stepping stone of the next antiparticle.
In 1957, B. Cook, G. RLanbretson, O. Pieeione and B. Wentzel of Berkeley began to look for the antinuclear partner of antiproton, that is, antineutron.Since the antineutron is not charged, it can not be directly detected, but can only be indirectly detected through its interaction, so it is more difficult to detect.Cook and others control the antiprotons and launch them into the liquid immersedLuminescent materialMedium;Then they letCharged particle detectorAutomatically record whether there are charged particles passing through;;Last beam encountersCherenkov counterGlass sheet.The experimenter found 74 cases (i.e. Cherenkov light that can represent the passing of antineutron), in which the incident antiproton apparently lost its charge on the initial scintillation target.Although no charged particles passed through the charged particle detector, the Cherenkov counter detected the interaction results.They believed that the antiproton lost its charge on the first target and turned into an antineutron, so it could not be seen when passing through the charged particle detector. It was only visible when the antineutron entered the nucleus of the Cherenkov glass and annihilated with a subnuclear particle and emitted the characteristic light of subnuclear fragments.With antiprotons and antineutrons, the next step is to make antinuclei.The first kind of nuclear antimatter was the anti deuteron synthesized by Italian physicist A.iZhcichi working at CERN in 1965.
Hydrogen atom is the simplest of all atoms. It is formed by a single electron orbiting around a proton.But in nature, one out of every 10000 hydrogen atoms is different. Although there is only one proton in its nucleus (otherwise it is no longer hydrogen), it has an additional neutron tightly bound to the proton.Because it has two atomic weights, this "heavy hydrogen" is called deuterium, and the simplest compound nucleus of proton neutron pair is called deuteron.When using a highly purified negatively charged particle beam to enhance the supply of antiprotons, Zikiki discovered the antideuteron, which is composed of an antiproton and an antineutron, and is as stable as an ordinary atomic nucleus.In fact, the material world is composed of atoms, and atoms are composed of protons, neutrons and electrons. Can antiprotons, antineutrons and positrons form anti atoms and become antimatter?In principle, it is possible for nitrogen atoms and anti nitrogen atoms to mirror each other, because the nuclear force that attracts protons and neutrons together and the electromagnetic force of atomic nuclei that attract electrons have the symmetry of positive and negative particles, that is, the force between a pair of particles is completely equal to the force between a pair of corresponding antiparticles.However, from an experimental point of view, there is almost no precedent to find natural anti elements on the earth or even in the universe, so we have to use accelerators to artificially manufacture anti nuclides and anti elements.[2]
On October 30, 1979, American scientists recently usedHigh-altitude balloon, measured theAntimatterStream.This is the first time that antimatter has been found outside the laboratory on Earth.
New Mexico State UniversityThe scientific researchers recently put a 60 story helium filled balloon 35 kilometers high.The balloon was loaded with 5000 pounds of high-sensitivity scientific detection equipment, including a 300 pound cryogenic devicesuperconductivityMagnets.The balloon flew high in the sky for 8 hours, and its magnetic field detected 28 antiprotons.
Scientists believe that this discoveryThe origin of the universeThe research of will have an important impact.[3]
First detection
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On August 9, 2011, according to the BBC, scientists first detected a narrow strip of antiproton particles circling the space near the Earth.This discovery was published in the Astrophysical Journal Letters, and the literature confirmed that the Earth's magnetic field can captureAntimatterparticleTheoretical work.At the same time, the research team said thatVan Allen radiation beltA small amount of antiprotons have also been found between the two layers of.Although the number is small, the research team believes that these antiprotons can provide enough fuel for future spacecraft.
The Pamela satellite launched in 2006 identified these antiproton particles, and its mission is to study the antiproton particles from the solar system and space outside the solar systemHigh-energy particleThe essence ofcosmic raysAnd searching for a small amount of possible existing in a large number of conventional substancesAntimatterParticles.High energy cosmic ray impact and breakthroughEarth's atmosphereMolecules in, forming freeparticle"Meteor Shower".Many cosmic ray particles and the substances formed by their impact on atmospheric molecules are finally captured by the Van Allen radiation belt. This doughnut shaped radiation zone isGeomagnetic fieldThe area where antiproton particles are captured.When the Pamela satellite passesSouth Atlantic Anomaly When the air above theCosmic spaceThe research team believes that there is a cluster of antimatter particles with a concentration thousands of times higher than that of conventional decayVan Allen radiation beltThe nearby antiproton belt, under the irradiation of light, collides with the conventional matter in the atmosphere, and finally disappears.
Alessandro Bruno of Bari University, the co author of the paper, said that this result confirmed the previous theoretical prediction that there really exists near the earthAntimatterBand.These antimatter and conventional matter can release huge energy when they meet, which is attracting people to explore the possibility of using antimatter as fuel to drive spacecraft.[4]
