Helicity


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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)

Helicity

 

(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.

helicity

[he′lis·əd·ē]
(quantum mechanics)
The component of the spin of a particle along its momentum.
References in periodicals archive ?
left, helicity, and therefore the charged star must generate only these.
1999) have predicted a helicial structure to the C--terminal domains, and for certain C--terminal recombinant peptides, this helicity has been determined with evidence supporting a functional coil to the helix transition at the C--terminal zone.
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.
However the violation of parity equires that the photons be emitted as an incoherent mixture of El and Ml radiations and therefore the radiation is left circularly polarized and the transfer of helicity from electron to photon approaches 100% at the end-point of the spectrum.
7 Synthesis and Application of Helical Polymers with Macromolecular Helicity Memory Hiroki Iida and Eiji Yashima
The sign selected in (3) reflects positive helicity (projection of the spin on the direction of momentum) corresponding to left-handed circular polarization.
The 97 papers here explore such areas as the solar interior and dynamo, the transition region and corona, flares and magnetic helicity, the three-dimensional structure of the outer atmosphere, solar wind and the interplanetary space, and possible anomaly in the current solar cycle.
At the time, it was expected that the main threat would be straight line winds, but low level hodographs were strong, with storm-relative helicity values of 300-400 J/Kg and upper air soundings with 0-6km shear at 50-60 kts.
In the absence of resonances it can be shown that the PV helicity dependence of the total cross section vanishes if only elastic scattering is present and that both the PV neutron spin rotation and the PV helicity dependence of the total cross section with inelastic channels are constant in the limit of zero neutron energy [23].
Thus, it ignores the effects of the curvature and helicity of the screw.
I was hoping that when we saw the crystal structure of the needles, we would see a lock-and-key phenomenon" accounting for the helicity of the aggregate, Fuchs says.
The spirals of the respective wire are not strictly parallel to the symmetry axis of the coil (the Oz axis) but they have a certain helicity (corkscrew-like path).