What is the origin of proton spin?

This is one of the important subjects in the elementary particle physics. The components of proton are valence quarks (two up quarks and down quark) and gluons. It is believed that the origins of proton spin are the quark spin, the gluon spin and the orbital angular momentum of quarks and gluons. The quark spin component is studied at CERN (EMC and SMC : polarized muon beam and polarized proton target) and SLAC (E80, E130, E142/E143 : polarized electron beam and polarized proton target). The gluon spin component and other spin parameters have been studied in E704 experiment.

The E704 experiment was performed using Fermilab Polarization/Spin Physics Facility at MP9 in the Meson Area of Fermi National Accelerator Laboratory, in which we used the world highest energy polarized beam (200 GeV/c). The magnet system for spin rotation, "Snake Magnet"(Spin rotation magnet), was used in order to change the direction of proton polarization. The beam definition system was placed upstream and downstream of Snake Magnet. As the experimental target, the liquid hydrogen target and the polarized proton target were used. The measurements were carried out using the set of the transversely-polarized proton/anti-proton beam and the liquid hydrogen target and the set of the longitudinally-polarized proton/anti-proton beam and the polarized proton target. Various spin parameters in the polarized proton-proton hard collisions were measured. Photons from reactions and photons from pi0 and eta mesons were detected using two set of lead glass arrays, CEMC1 and CEMC2. Charged particles were detected using the multiwire proportional chambers placed between PPT and CEMC's.

The data analysis has been already completed.

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by Seiji Makino
Oct.26, 2000