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Helicity (quantum mechanics)

A fundamental quantized variable used in quantum mechanics to specify the relative orientations of spin and linear momentum of massless particles. It is a requirement of fundamental Dirac quantum mechanics that such particles have their spins aligned either parallel or antiparallel to their linear momentum. Particles having parallel alignment are arbitrarily assigned helicity +1; those having antiparallel alignment, -1. See Momentum, Spin (quantum mechanics)

In a classic experiment on K electron capture by 152Eu, M. Goldhaber, L. Grodzins, and A. Sunyar first showed that the neutrino emitted in the weak nuclear interaction had negative helicity—that its spin was aligned antiparallel to its momentum. An equivalent description of this situation is that these neutrinos are left-handed. Symmetry requires that antineutrinos be right-handed and have positive helicity. See Electron capture, Elementary particle, Neutrino, Quantum mechanics, Symmetry laws (physics)



(η), a fundamental quantized variable (quantum number) characterizing the state of elementary particles. It is the projection of the spin of a particle on the direction of its motion. If η > 0, the particle is said to have right-hand, or positive, helicity; if η < 0, the particle has left-hand, or negative, helicity.


(quantum mechanics)
The component of the spin of a particle along its momentum.
References in periodicals archive ?
Currently, the Helicity is focused on the city tour.
Cohen and his colleagues, however, found the increases in outbreaks were driven instead by storm relative helicity, which has not been projected to increase under a warming climate.
However, neutrinos and antineutrinos can be told apart since they have a different direction of spin, or helicity.
Topics include the relation between magnetic energy and helicity, the hydrodynamics of colliding circumstellar bubbles, the stability of cosmic ray precursors, supernova remnants as the source of galactic cosmic rays, and polarimeters for HARPS and X-shooter.
The relative stereochemistry was determined by comparing the coupling constants with the literature [17-20] and the absolute configuration was deduced from the positive Cotton effect by application of the helicity rule for conjugated transoid ketones in CD spectrum.
By comparing average atmospheric conditions with average monthly tornado counts in regions across the United States, they identified two parameters that seemed closely associated with monthly tornado activity: rain associated with strong updrafts; and helicity, which measures the tendency of winds to spin those updrafts.
Helicity fluctuations and turbulent energy production in rotating and non-rotating pipes.
Carbon nanotubes have many structures, differing in length, thickness, type of helicity and number of layers.
Papers from joint discussions at a July 2003 meeting are organized in sections on non-electromagnetic windows for astrophysics, mercury, magnetic fields and helicity in the sun and heliosphere, astrophysical impact of abundances in globular clusters, and white dwarfs.
1999) who determined the helicity of [alpha] (404-451) and [beta] (394-445) tubulin C-terminal recombinant peptides with the use of NMR (nuclear magnetic resonance).
There is an extensive research program at ISAC that ranges from measuring the distribution of protons within the very neutron-rich Li nucleus, magneto-optical trapping to allow the study of the helicity of neutrino emission in [beta] decay in a search for the new physics grail, surveying and analyzing the very weird shapes the nucleus can take, and exploring possible approaches to produce new superheavy elements using radioactive beams.