helicity

noun

1. (countable, uncountable)The quality of being helical.
2. (countable, uncountable)Any of certain measures of the extent to which vortex lines (in fluid flow) or field lines (in a magnetic or electromagnetic field) kink and twist or link and coil around one another.

   “The conjecture made in Tsinober and Levich (1983) was that coherent structures should possess a significant coherent helicity.”

   “The helicity associated with the writhing number is obtained by observing that a torus with twist number ±1 may be distorted into a figure-8 configuration which appears untwisted.[…]Note that at each step the total helicity, consisting of the sum of twist, kink, and link helicities, is conserved.”

   “Thus the total helicity H equals the sum of the entries in a matrix Hᵢⱼ. If N is large then there will be many more mutual helicity terms. In this case ignoring the self helicities (if they are difficult to observe) may only give a small error.”

   “Now conservation of helicity is maintained: the writhe of the loops in the second panel is compensated for by the opposite sign of the twist helicity along the loops.”

3. (countable, uncountable)The quantized spin component of a moving particle along the direction of its motion.

   “1989, John Taylor, 17: Gauge theories in particle physics, Paul Davies, The New Physics, Cambridge University Press, 1992, 1st Paperback Edition, page 467, To understand this name, note that the helicity is, roughly speaking, the spin in the direction of motion.”

   “The experiment was particularly ingenious because, as the neutrino hardly interacts with matter, some way of indirectly measuring its helicity had to be devised.”

   “Interpreted in terms of helicity, this means that if the incident electron has positive helicity, then the outgoing electron has positive helicity for forward scattering, and negative helicity for backward scattering.”