advanced_notions:elementary_particles
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advanced_notions:elementary_particles [2017/09/10 17:08] jakobadmin [Student] |
advanced_notions:elementary_particles [2018/04/14 10:08] (current) aresmarrero [Abstract] |
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| ====== Elementary Particles ====== | ====== Elementary Particles ====== | ||
| - | <tabbox Why is it interesting?> | ||
| - | |||
| - | <tabbox Layman?> | ||
| - | [[http://www.ejsme.net/articles/52/523.pdf|Why not start with quarks? Teachers investigate a learning unit on | + | <tabbox Intuitive> |
| - | the subatomic structure of matter with 12-year-olds]] by Gerfried J. Wiener, Sascha M. Schmeling and Martin Hopf | + | |
| + | * A nice overview is given here: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/ | ||
| + | * [[http://www.ejsme.net/articles/52/523.pdf|Why not start with quarks? Teachers investigate a learning unit on the subatomic structure of matter with 12-year-olds]] by Gerfried J. Wiener, Sascha M. Schmeling and Martin Hopf | ||
| + | * [[https://gravityandlevity.wordpress.com/2015/04/11/how-big-is-an-electron/|How big is an electron?]] by Brian Skinner | ||
| | | ||
| - | <tabbox Student> | + | <tabbox Concrete> |
| + | {{ :advanced_notions:elemparticles.png?nolink |}} | ||
| + | |||
| + | ---- | ||
| <blockquote> | <blockquote> | ||
| In the 1970’s, high energy physicists pursued Lie algebra theory as a valuable tool to characterize all the gauge interactions. These are now understood to be SU(3) for the strong force (which describes the interacations between quarks, which are the constituents of hadrons such as the proton), and SU(2) × U(1) for both the weak and electromagnetic interactions of quarks and leptons (such as the electron). This is an important feature of the standard model of particle physics [YM,We,Sa,Gl]. Grand unification was an effort to combine these symmetries as subgroups of a unifying group such as SU(5). Superstring unification provides an alternative mechanism to combine symmetries. | In the 1970’s, high energy physicists pursued Lie algebra theory as a valuable tool to characterize all the gauge interactions. These are now understood to be SU(3) for the strong force (which describes the interacations between quarks, which are the constituents of hadrons such as the proton), and SU(2) × U(1) for both the weak and electromagnetic interactions of quarks and leptons (such as the electron). This is an important feature of the standard model of particle physics [YM,We,Sa,Gl]. Grand unification was an effort to combine these symmetries as subgroups of a unifying group such as SU(5). Superstring unification provides an alternative mechanism to combine symmetries. | ||
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| <cite>https://arxiv.org/pdf/hep-th/9601117.pdf</cite> | <cite>https://arxiv.org/pdf/hep-th/9601117.pdf</cite> | ||
| </blockquote> | </blockquote> | ||
| - | <tabbox Researcher> | + | |
| + | <blockquote> | ||
| + | Recall that in the flat spacetime case the particle states are labeled by the Poincar´e label (p, λ), whose values are closely related to the UIR label (m, s); m is used to define the mass-shell condition and s determines the range of λ. We identified m with the mass of the field quanta, and s with the spin. In a group theoretical sense, we associate these parameters with the eigenvalues of the Casimir operators (see section 3.5). | ||
| + | |||
| + | <cite>http://thep.housing.rug.nl/sites/default/files/theses/Master%20thesis_Marco%20Boers.pdf</cite> | ||
| + | </blockquote> | ||
| + | |||
| + | <tabbox Abstract> | ||
| + | <blockquote>A question not often addressed when discussing the standard model is how one describes physical | ||
| + | particles. Taking the electron as an example, the assumption usually made is that the free Dirac | ||
| + | spinor in the interacting theory, at asymptotic times, can be viewed as an electron since ‘the coupling | ||
| + | switches off’. This would mean that what is being caught in a detector is really a free fermion. The | ||
| + | problem here, of course, is that in QED and QCD the coupling does not switch off, and assuming | ||
| + | it does so generates infrared divergences. As a result, the spinors do not become free even at | ||
| + | asymptotic times [1, 2], nor do they ever become gauge invariant. [...] | ||
| + | |||
| + | The physical picture is of a matter particle | ||
| + | surrounded by a cloud of ‘photons’, neither of which are individually observable, but which together | ||
| + | constitute a gauge invariant, physical particle. This description is nonlocal, which is an immediate | ||
| + | consequence of gauge invariance, but observables calculated with our states are manifestly local and | ||
| + | correctly reproduce classically expected physics. | ||
| + | |||
| + | <cite>[[https://arxiv.org/abs/0907.4071|Stability, creation and annihilation of charges in gauge theories]] by Anton Ilderton, Martin Lavelle, David McMullan</cite> | ||
| + | |||
| + | |||
| + | </blockquote> | ||
| + | |||
| + | ----- | ||
| + | |||
| + | * http://math.ucr.edu/home/baez/qg-spring2003/elementary/ | ||
| + | * See http://physics.stackexchange.com/questions/33350/particle-as-a-representation-of-the-lorentz-group | ||
| + | * [[http://www.pnas.org/content/99/1/33.full.pdf|A closer look at the elementary fermions]] by Maurice Goldhaber | ||
| + | |||
| + | ----- | ||
| <blockquote> | <blockquote> | ||
| Line 33: | Line 69: | ||
| </blockquote> | </blockquote> | ||
| - | + | <tabbox Why is it interesting?> | |
| - | <tabbox Examples> | + | |
| - | --> Example1# | + | Elementary particles are the fundamental building blocks and also responsible for the fundamental interactions like electromagnetism. |
| + | <tabbox FAQ> | ||
| - | + | --> How large is an elementary particle?# | |
| - | <-- | + | |
| - | --> Example2:# | + | See https://axelmaas.blogspot.de/2018/02/how-large-is-elementary-particle.html?m=1 |
| + | <-- | ||
| - | + | -->Why do physicists believe that particles are pointlike?# | |
| + | see https://physics.stackexchange.com/questions/41676/why-do-physicists-believe-that-particles-are-pointlike | ||
| <-- | <-- | ||
| | | ||
| <tabbox History> | <tabbox History> | ||
| + | <blockquote> | ||
| + | Gell-Mann’s version of the Eightfold Way had predicted that the pro-ton, the neutron, and all the other thus-far observed strongly interactingparticles could in principle be made out of three smaller subparticlescalled quarks. Quarks, if they existed, had to be almost unbelievablypeculiar; they had to carry a fractional electric charge of either one-third or two-thirds the charge of the proton, but no one had ever seena particle of fractional charge. Although the Eightfold Way impliedtheir existence, physicists were reluctant to take them seriously. Instead,avoiding the reality behind their mathematics, they had come to thinkof quarks as mathematically consistent but fictitious components thatcould never be observed. It was as though the only coins you had everseen in circulation were nickels, dimes, and quarters, and you had con-cluded that somewhere there had to be a one-cent coin. | ||
| + | If a proton really contained three hard little quarks deep inside it, oneshould be able to “see” them experimentally by shooting a fast electronat a proton and observing it recoil sharply when it struck a quark head-on.The method is a little like looking for bits of eggshell in a spongecake—once in a while, as you chew, you hear a sharp crack as your teethhit a fragment of shell. | ||
| + | Robert Hofstadter, my cousin’s City College friend of the 1930s, hadobserved no such sharp recoils, and everyone had concluded that theproton was pure sponge and no eggshell. Hofstadter’s experiments, how-ever, were limited. He had kept an eye only on the so-called elasticcollisions, those in which the target proton remained intact as it recoiledlike a struck billiard ball. Now, in the late 1960s, a later generation ofphysicists at the Stanford Linear Accelerator Center (SLAC) began towatch so-called inelastic electron-proton collisions in which the protondisintegrated rather than recoiled after being struck. Amazingly, in thesecollisions, many of the electrons did in fact recoil sharply, as though theyhad struck something very hard and small. Somewhere deep inside theretruly were bits of eggshell. | ||
| + | |||
| + | <cite>From My Life As A Quant by Emanuel Derman</cite> | ||
| + | </blockquote> | ||
| </tabbox> | </tabbox> | ||
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