In a bubble chamber, charged particles travelling through the medium in the chamber leave a track that can be photographed. Neutral particles and stationary particles don’t produce tracks, so they don’t show up in bubble chamber images. This image was captured by the 2 m bubble chamber at CERN in 1972. This bubble chamber was filled with liquid hydrogen. Energetic protons were fired into the chamber from the left. The protons collided with the hydrogen atoms and produced other particles that then collided, decayed, or escaped. A uniform magnetic field (pointing out of the page in this image) caused the charged particles to travel along a curved path.
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Daily usage of Antimatter
Daily usage of Antimatter
Positron emission tomography (PET) is a medical imaging technique that utilizes the annihilation of matter and antimatter. Radioactive tracers are injected into, or swallowed by, the patient and collect in the tissue being studied. The tracers emit positrons that annihilate electrons in the tissue, producing two gamma rays that leave the body and are detected. The data is translated into an image showing where the most active tissue is located.
What is antimatter?
What is antimatter?
Antimatter was first predicted when English physicist Paul Dirac combined quantum mechanics and special relativity. He obtained a result that predicted the existence of negative energy levels, and the only way to make sense of this result was to postulate the existence of antimatter, an achievement for which he won the Nobel Prize in Physics in 1933.
The usual analogy for antimatter is that when you take the square root of a number, there are two possible answers, one positive and one negative. Symmetry and conservation laws reveal that whenever a process produces a particle, an antiparticle must be produced. Particles in the Standard Model are identified by properties such as mass, spin, and electric charge. Antiparticles have the same mass as their counterparts, but other properties are reversed. Antiparticles can be combined to produce antiatoms, so a positron bound to an antiproton is called antihydrogen. All experimental tests to date indicate that antihydrogen has the same physical properties as hydrogen, except that the nucleus is negative and the surrounding charge is positive.
What are Feynman diagrams?
What are Feynman diagrams?
Feynman diagrams—named after American physicist Richard Feynman—are symbolic representations of possible interactions between particles. They are tools that help us express the mathematics needed to calculate the probability of each possible outcome when particles interact. They do not represent what actually happens during the interaction; rather, they are a short-hand method for calculating what could happen. In quantum physics, if an interaction is not directly observed there is no way of knowing the specific process that occurred in that interaction. One of the most important consequences of the mathematics is that as the diagrams get more complicated the possible outcomes become less likely to happen. This means that although there are countless possibilities, we need only consider the simplest events in many cases.
There are two basic components to Feynman diagrams in quantum electrodynamics (QED): solid lines for fermions and wavy lines for photons. To represent a real process requires at least two vertices. The lines that enter and leave the diagram represent real particles that can be observed. The lines that begin and end inside the diagram represent virtual particles that cannot be observed.
How are conservation laws and symmetry related?
Conservation laws describe what physical processes do and do not occur in nature; symmetry describes an object or process that looks the same after an action has happened. German mathematician Emmy Noether showed how each conservation law is associated with a fundamental symmetry. For example, conservation of energy is associated with a time symmetry, which means a process does not depend on when it happens.
Part of CERN’s antimatter factory is shown here. The antiproton decelerator is behind the concrete blocks on the far left.
All information above courtesy of PERIMETER Institute: Beyond the Atom
What is the antimatter factory?
The antimatter factory is a facility at CERN that is equipped to produce and study antiparticles and antimatter. The process begins when a beam of high-energy protons is fired at a metal target, producing antiprotons, along with many other particles. The antiprotons are collected using carefully designed magnetic fields and directed into the antiproton decelerator (AD), which slows the antiprotons down so they can be used to make antimatter. The AD uses the same basic technique as a particle accelerator but, instead of increasing the energy of the beam, it decreases the energy until the antiprotons can be contained in a trap. Once the antiprotons are contained, they can be combined with positrons from another source to produce antihydrogen, just as regular protons combine with electrons to form hydrogen.
Components of a Feynman diagram
Components of a Feynman diagram
Feynman diagrams are a useful tool to visualize and understand what is happening in particle interactions. They were invented by and named after the American physicist Richard Feynman.
Each line in the diagram represents a particle:
a straight line with an arrow represents a matter particle.
a wavy line represents either a photon or a weak boson.
a coiled line represents a gluon.
Time is usually represented horizontally.
So lines that begin on the left represent particles that are present before the interaction whereas lines ending on the right represent particles that are present after the interaction.
The arrows do not represent the direction of a particle. An arrow to the right represents a particle whereas an arrow to the left represents an anti-particle.
Interesting comment about the Higgs Boson discovery.
a dashed line represents a Higgs boson.
Particle:
Anti-Particle:
A bit of mixing the qualitative with quantitative...
Vertices
The point where three or four lines meet is called a vertex and this represents a particle interaction. The vertices represent either the electromagnetic, the strong, the weak or even the Higgs interactions. The diagram below shows the basic vertices for the electromagnetic interaction, the strong interaction and the weak interaction.
Rotation
Feynman diagrams are flexible. The individual lines or the diagram as a whole can be rotated freely. For example, the lines can be rotated around a vertex to show different types of interaction. The four vertices below show the possible interactions when an electromagnetic interaction vertex is rotated.
(a) annihilation of an electron and a positron into a photon
(b) pair production of an electron and positron from a photon
(c) absorption of a photon by an electron (similar to Bohr Model Excitation)
(d) emission of a photon by an electron (the production of a photon, by an electron moving to a lower energy level)
Make your Own Feynman
Make your Own Feynman
Use the GeoGebra simulation below, created by Chris Hamper, to recreate the four interactions shown above. Click on the blue dots to move the lines. (the photon in this simulation is represented by a dashed line instead of the usual wavy line)
Higgs interaction
Measurements of the Higgs boson at CERN show that it transforms into a particle-antiparticle pair after 10-22 s. Certain particle-antiparticle pairs are more likely - the boson is more likely to transform into pairs of more massive particles. The Feynman diagram represents a Higgs boson transforming into a tau-antitau pair.
Complete Feynman diagrams
Complete Feynman diagrams
A complete interaction can be constructed by combining two vertices together. For example the diagram below represents the attraction of an electron with a positron via the electromagnetic interaction.
The above diagram can be rotated to represent another interaction. The diagram below represents the annihilation of an electron and positron into a photon followed by the pair production of another electron-positron pair.
Beta decay (transformation)
Beta decay (transformation)
The Feynman diagram below shows represents a beta-plus decay (transformation). In beta-plus decay a proton transforms into a neutron emitting a positron and a neutrino.
In fact an up quark in the proton (uud) is transforming into a down quark to become a neutron (udd) by the emission of a W plus boson. From the boson a positron-neutrino pair are produced.
Additional Feynman Resources:
Additional Feynman Resources:
Kognity - Section 7.3 - Use your ACS login
OpenStax - Four Basic Forces
IB Physics Standard Model.pdfPage updated
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