|Date||November 3, 2017||Time||3:35 - 5:00 pm|
|Location||Baylor Sciences Building, Room A.202|
Lattice QCD Calculation of Glue Spin and Helicity in the Proton
The spin of a particle is an important property that can affect the dynamics of the system. While the spin of the proton is known, it is still unknown what contributes to its observed spin. The origin of the proton spin is one of the major unsolved problems in physics and is referred to as the “Proton Spin Crisis.” Deep-inelastic scattering experiments have shown not only that quarks contribute a mere 30% of the overall proton spin, but that there is a nonzero glue helicity G within the proton. A Lattice Quantum Chromodynamics (QCD) calculation was performed for a theoretical determination of the contribution of the gluons to the proton spin. The calculation is the first of its kind and took advantage of the Coulomb gauge fixing condition and the IMF limit in order to determine the glue helicity operator . While early QCD models predicted the gluon to contribute less than about 1% of the proton’s spin, this calculation determined that the gluons account for roughly 50% of its net spin. While the theoretical predictions of the total parton spin is still less than the observed proton spin, it still provides a new understanding of the contribution of the gluons to the proton spin which was once believed to play a near insignificant role.
Reference: Y. Yang et al., Phys. Rev. Lett. 118, 102001 (2017).
Nonlinear Driving Response of Vertical Paired Structure in Complex Plasma
Vertical chain structure of multiple Melanmine Formaldehyde (MF) particles (mainly two particles chain) was formed in a glass box in modified Gaseous Electronics Conference (GEC) reference cell with a sinusoidal drive on the lower electrode. Particle responses were studied under different driving parameters. Amplitude-frequency responses were fitted at different frequency regions which gave the information of particle-particle interaction as well as the other parameters.
Reference: A.V. Ivlev et al., Phys. Rev. Lett. 85, 4060 (2000)
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