Proton Spin Crisis Downgraded
After at least 3 decades, scientists may finally have a decent handle on the mystery of where proton spin comes from. Particle spin in this context is essentially a form of inherent angular momentum analogous to a spinning top but like all analogies (especially Quantum Mechanical ones), they only take understanding so far.
It was assumed as a no-brainer that the spin of a proton is derived from the spins of its constituent particles; makes perfect sense right? In this case that means that the spins of the 3 quarks that make up each proton determine its spin. In 1987 however, the European Muon Collaboration at CERN shocked the physics community when it revealed experiments showing that quark spin accounts for only 30% of the total proton spin.
Where the hell does the other 70% come from? This has been dubbed THE PROTON SPIN CRISIS.
Doesn’t sound like much of a crisis to you? Well physicists were reasonably agitated. This would be like an experiment showing that 2 + 2 = 13.3. I’m sure mathematicians would freak a little and may even call it the ADDITION CRISIS. These results could also mean that a very cool and fundamental theory called Quantum Chromodynamics is wrong.
Quantum Chromodynamics (QCD) was developed in 1973 to describe how the strong force (the strongest in nature) works. Essentially, this force derives from force particles, called gluons which are transmitted between various flavors of quark particles. A residue of this force is also transmitted between particles that are made of quarks like the proton and the neutron which make up the cores of atoms.
Recent scattering results from experiments at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory in New York have now implicated the spin from Gluons themselves as a contributor of another 40% of a proton’s spin.
That now leaves only 30% of the proton spin unaccounted for which has mollified the physicists quite a bit.
I believe it is now warranted to downgrade the Proton Spin Crisis to perhaps the Proton Spin Concern or maybe even the Proton Spin Mild-Unease.
Image Credit: Brookhaven National Laboratory