Also found in: Dictionary, Wikipedia.

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)

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(quantum mechanics)
The component of the spin of a particle along its momentum.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Structure of Helicity and global solutions of incompressible Navier-Stokes equation.
* Helicity is given by the helical translation motion (v > 0), which can be left-handed or right-handed.
Currently, the Helicity is focused on the city tour.
However, the differing outflow evolution could also be due to the increasing magnitudes of the capping inversion and lowlevel storm-relative helicity towards the east.
The effective parameters along the propagation direction within the helicoid are dependent on helicity as the pitch varies when other geometric parameters remain constant.
However, as shown in [34], conservation of magnetic helicity severely restricts fast dynamos.
Heinz, "Control of valley polarization in monolayer Mo[S.sub.2] by optical helicity," Nature Nanotechnology, 2012.
There was a strong peak at 218 nm, which indicated the helicity of dsDNA [42].
The helicity can be employed to measure the alignment or misalignment of the local velocity and vorticity vectors, and the rotating direction of the helical structures was indicated by the sign of helicity [21].
Today we usually assign these two states as two eigen states of helicity p[sigma]/p belonging to eigen values [+ or -] 1, but we can assign two arbitrary, mutually orthogonal states instead.
To understand the increased frequency in tornado outbreaks, the researchers looked at two factors: convective available potential energy, or CAPE, and storm relative helicity, which is a measure of vertical wind shear.