Question: The [spinor helicity formalism](http://isites.harvard.edu/fs/docs/icb.topic1146666.files/IV-3-SpinorHelicity.pdf) is a modern technique widely used in scattering amplitude calculations nowadays. However, it is hard to find a reference for who first came up with the formalism. Maybe someone here knows of the first author to ever use spinor helicity?

EDIT:

Even [this review](http://arxiv.org/pdf/1308.1697v2.pdf) does not have any reference on the topic. However, they naturally introduce it from a discussion on Dirac and Weyl spinors, so I guess one can attribute the formalism to them.

Answer: 
Apart from that there are also bunch of papers which are regarded as earliest developments of spinor helicity formalism, for example

<http://inspirehep.net/record/167680?ln=en>

<https://www.sciencedirect.com/science/article/pii/0550321382904898>

<http://inspirehep.net/record/231187?ln=en>

<http://inspirehep.net/record/302550?ln=en>

Dixon cite those in his review paper

<https://arxiv.org/abs/1310.5353>
Check out this, I guess this is the first paper where it was introduced. <http://www.sciencedirect.com/science/article/pii/0550321385902858>