ANTIMATTER. A beam of particles is a very useful tool. Antimatter! 1

Transcription

1 ANTIMATTER A beam of particles is a very useful tool. Trans Atlantic Science School 2016 Antimatter! 1

2 Antimatter History! 3 Theory and properties! 4 Producing antimatter! 6 Antimatter research! 7 Fermilab s programs which use antimatter! 8 Use! 8 Ideas using antimatter to treat cancer! 9 Unsolved mysteries! 9 Antimatter! 2

3 ANTIMATTER History The first theories of antimatter were presented in the 1880 s. Arthur Schuster was the first who used the term antimatter and antiatoms. Paul Dirac presented the modern theory of antimatter in It was the first theory which predicted the existence of antimatter. He explained it with a theory called Dirac Sea. Dirac supposed that there could be particles which have negative energy. These particles could construct antimatter. Afterwards better theories has been explained and Dirac Sea has been forgotten. Carl Anderson was the first person who found an antiparticle. He studied the masses of different particles in He used a mist chamber and magnetic fields. Every time a particle went through the chamber it left small mark of its trajectory. Anderson noticed that there should be particle which has the same mass as an electron but an opposite electric charge. He called it a positron.!!!!!!! Over twenty years later in 1955, Emilio Serge and Owen Chanberlain found the next piece of antimatter. Their team discovered antiprotons. An antiproton, like a positron, has an opposite charge but the same mass as a massive particle. A year later in 1956, an antineutron was found in the same place. Antineutrons have no charge, but their properties were opposite in comparison with a neutron. This is caused by quarks inside the neutron. After the 1960 s new antimatter particles were found. New theories have been shown and some of these have been proved. In the year 1965, they were able to construct antideuteron atoms at CERN. They succesfully combined antineutrons and antiprotons. ~enqvist artikkeli.dir Antimatter! 3

4 Theory and properties Every particle has an antiparticle, or the particle is its own antiparticle. Antimatter particles are frequently written with a bar on top. Antimatter particles have the same mass as their matter particles. Annihilation between matter and antimatter particles produces energy equal to E=mc2, which means that if one gram of matter and one gram of antimatter annihilate, the produced energy is equal to * 10^15 joules. It is the same amount of energy as 50 kilotons of TNT. Annihilation between antimatter and matter particles produces gamma rays (high energy photons). In each annihilation the momentum needs to be conserved which means that it needs to produce two photons. Antiparticles are involved in many matter interactions. For example radioactive B+-decay produces positrons. Pions (π+) decay to antimuons and muon neutrinos. The quantum properties of antimatter particles are opposite to those of matter particles. For example, charge, lepton, baryon and spin quantum numbers are opposite. Such properties are involved in lepton and baryon number conservations in particle physics. Antimatter! 4

5 Baryon numbers (within the brackets): anti-u (-⅓) + anti-u(-⅓) + anti-d(-⅓) -> anti-uud (-1) = anti-proton -> (-⅓)+(-⅓)+(-⅓)=-1 -> 0=0 Lepton numbers: Antimatter is produced in so called pair production. Pair production is a mechanism where neutral boson (example Z boson or photon) decay to particle-antiparticle pair. The minimum energy that pair production needs for the original particle is at least the rest-mass energy of the production particles (in electron s and positron s pair production the minimum of energy needed is equal to MeV). Pair production decays need to conserve all particle properties, but it also needs to conserve momentum. That means that pair production can`t happen in empty space and the original particles need, for example, atoms to interact with. Antimatter atoms have positively charged positrons orbiting negatively charged nucleus, whereas matter atoms have negatively charged electrons orbiting positively charged nucleus. Antimatter nucleus negative charge comes from antiproton s negative charge (matter s positive charge comes from protons positive charge). Antiproton s negative charge is product of it s up and down quarks opposite elementary charge to protons (proton is made of two up-quarks (charge +⅔) and one down quark (charge -⅓)). Anti up-quark has -⅔ and anti down-quark has +⅓. University Physics: Young & Freedman Antimatter! 5

6 Producing antimatter Antimatter is commonly produced by particle accelerators. Accelerators use acceleration cavities which are powered with electromagnetic waves to speed up protons. First protons are accelerated to collide with the metal. Some of the energy released in the collide transforms into matter (protons) and antimatter (antiprotons). Positrons are produced in pair production, for example irradiation matter by gamma-rays. Positrons are also produced naturally in β+ decay. Producing antiatoms (antihydrogen and antihelium) positrons and antiprotons have to put together. To store antimatter devices called traps which keeps antimatter away from ordinary matter. Usually traps use electric and macnetic forces which keep antimatter in the center whitout touching walls. Storing atoms with neutral charges is much more complicated. Neutal antiatoms must be stored only with magnetic trap. Antimatter! 6

7 Antimatter is produced also in nature: β+ decay and pair production produces positrons. Antimatter, antiprotons and positrons, enters the athmosphere in cosmic rays, but less than 1% of the particles in cosmic rays are antimatter. Research by the American Astronomical Society discovered antiprotons originating above thunderstorm clouds. Them are produced in gamma-ray flashes (strong electric fields in the clouds accelerate electrons which creates gamma-rays). Antimatter research Experiments are using mainly antiprotons to study the properties of antimatter. Produced antiprotons have high energy level and almost speed of light so them have to slow down so that physicists can research their properties. The challenge is to create antiatoms and keep them away from ordinary matter for long enough to study them. At CERN antiprotons are made in the Antiproton Decelerator (AD) which provides low energy antiprotons for antimatter studies. First a beam of protons is fired into a block of metal. The energy from collision can create a new proton-antiproton pair. About one proton-antiproton pair is created in every million collisions. AD makes low energy antiproton beam. Focusing magnets keep antiprotons on the same track and strong electric fields slow them down. Antiprotons go out of AD when they travel 10% of speed of light. Then antiprotons go to studying experiments, for example ACE, AEGIS and ALPHA. ACE studies the biological effects of antiprotons. AEGIS uses antiprotons to measure Earth s gravitational acceleration. ALPHA makes, captures and studies antihydrogen atoms and compares with hydrogen atoms. In 2011 it had succeeded trapped antimatter atoms for over 16 minutes Antimatter! 7

8 Fermilab: Fermilab makes antiprotons by collide protons against a nickel. Fermilab used particle accelerator called Tevatron. Tevatron was the world s highest-energy particle accelerator until the year 2009 and the second most powerful particle accelerator before it shut down on September 29, It accelerated protons and antiprotons. Accelerator makes about 20 antiprotons for every 100 million protons they collide with the target.then they are collected in the accumulator. The antiprotons are transfered over to the Recycler ring and then cooled. Antiprotons are cooled so them are easier to study. Fermilab s programs which use antimatter Fermilab E-906/SeaQuest The Fermilab E-906/SeaQuest experiment is designed to measure the quark and antiquark structure of the nucleon and the modifications to that structure. The primary focus of this experiment was to measure the asymmetry of down and up antiquarks in the nucleon sea. The experiment was started in 2010 and collected data for 2 years. Use Nowadays antimatter is used in positron emission tomography (PET). The PET-device produces a three-dimensional picture of the functional processes in the body. It detects pair of gamma rays emitted by electron-positron annihilation. In the future it might be possible to use antimatter particles as an energy source because in accordance with Einstein s famous equation of mass-energy equivalence, a small amount of antimatter mass can be converted into a huge amount of energy. Currently we have problems producing and storing antimatter and it s also difficult to utilize the released energy. Matter-antimatter annihilation could be used as a fuel for example interplanetary travel if scientist solve the problems some day. Antimatter! 8

9 Ideas using antimatter to treat cancer Antimatter is used to treat cancer. Positrons are beamed through a tissue in such velocity that they do not annihilate until they encounter with cancer cells. Formed gamma rays damage the cancer tissue. There has also been theories of antimatter weapons. Annihilation could be used in a bomb instead of nuclear fission. It would raise a lot the mass-to-energy ratio of the system because matter-antimatter annihilation releases much greater amount of energy than nuclear fission. Antimatter could also be used as a powerful trigger mechanism in nuclear bomb. The method is called antimatter-catalyzed nuclear pulse propulsion. // // // Unsolved mysteries Theories wich haven t been proved Paul Dirac proposed that every particle of matter should have an antimatter counterpart. However, we are able to detect only matter particles in the universe. According to the latest research, antimatter particles annihilated soon after the big bang. The interesting question is why there is still matter which forms our universe? // Scientist have proposed many theories which haven t yet been confirmed. The most popular theory tells that there was slight difference between annihilated amounts of matter and antimatter particles few seconds after the big bang. The another theory says that all of the antimatter particles haven t annihilated. It would mean that somewhere there is an isolated part of the universe which is consisted of antimatter. // // In era after the Big Bang, when strong- and electroweak interactions were converged (known as Grand Unified Theory-era: GUT-era), there could be asymmetry between matter and antimatter because baryon numbers didn t need to conserve. After the Antimatter! 9

10 GUT-era the electroweak interactions should ve balanced the asymmetry between matter and antimatter. This being the case, the asymmetry should ve had happened at a much later epoch. It s known that antimatter have the same kind of mass than antimatter, but how does the gravity influence between matter and antimatter? If we could have an apple made of antimatter and drop it here on earth, would the apple go up? At the time world-class scientist are trying to find funding to a project where they are trying to cool antimatter molecules near the absolute zero by lasers to research how gravity affects to antimatter Nowadays it s very hard to produce antihydrogen, but some day it might be possible to create anti-diamonds or anti-deoxyribonucleic acid (DNA)? It s much easier to control charged anti-particles because them can be controlled by magnetic fields, but soon as we are producing antiatoms with no charge, things get complicated because those antiatoms start to annihilate with matter. It would take many years to develop the technology for producing complicated anti-atoms. Finding an antistar which produces heavier elements would be easier to use in a research but might be impossible to find Antimatter! 10