helicity

Noun

helicity (countable and uncountable, plural helicities)

1. The quality of being helical.
2. (fluid mechanics, electrodynamics) 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.1991, E. Levich, L. Shtilman, “Helicity Fluctuations and Coherence in Developed Turbulence”, in D. Schertzer, S. Lovejoy, editors, Non-Linear Variability in Geophysics: Scaling and Fractals, Kluwer...
   • 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.1995, G. E. Marsh, “2: Helicity and Electrodynamic Field Topology”, in Terence William Barrett, Dale M. Grimes, editors, Advanced Electromagnetism: Foundations, Theory and Applications, World...
3. (quantum mechanics) The quantized spin component of a moving particle along the direction of its motion.
   • To understand this name, note that the helicity is, roughly speaking, the spin in the direction of motion.1989, John Taylor, 17: Gauge theories in particle physics, Paul Davies, The New Physics, Cambridge University Press, 1992, 1st Paperback Edition, page 467
   • The experiment was particularly ingenious because, as the neutrino hardly interacts with matter, some way of indirectly measuring its helicity had to be devised.1999, Gustavo Castelo Branco, Luís Lavoura, João Paulo Silva, CP Violation, Oxford University Press, page 12