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Proton Spin Dissected  
Recent papers by the Phenix and the STAR collaborations, and theoretical analysis of the data conclusively indicate that about 20-30% of the proton spin is due to gluons.

The new precision measurements at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory based on data collection runs by the two experiments in 2009. The analysis of the proton spin was made possible by RHIC's unique capability of colliding polarized protons. According to Abhay Deshpande "the contribution of the gluons is about the same as the contribution of the quarks, 15%, measured at CERN in the 1990's. The remainder is due to the orbital motion of gluons and quarks. While there is evidence from transverse spin effects for the orbital motion, it can be only measured if we build the electron-ion collider (EIC) that is currently in the planning stage. Once EIC measures the orbital component directly we will have a complete understanding of the composition of the nucleon spin."

Kieran Boyle (currently a Riken BNL Research Center Fellow) and Andrew Manion (currently a postdoc at Lawrence Berkeley Laboratory) did the main data analysis for Phenix results during the time when they were graduate students in our Department.


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