Quarks match predicted asymmetrical behavior based on spin

Science : Spin is one of the fundamental properties of particles and is generally characterized as being up or down. In many situations, it does not matter whether a particle’s spin is up or down. A major exception to this, known as parity violation , occurs when electrons interact with atomic nuclei, which causes the scattering patterns of up- and down-spin electrons to become asymmetrical. The standard model predicts that this asymmetry is also present in the behavior of quarks. Now, Xiaochao Zheng of the University of Virginia in Charlottesville and her colleagues have confirmed that prediction. They bombarded deuterium nuclei with 190 billion up- and down-spin electrons that were just energetic enough to cause a quark to be ejected from the nuclei. They then measured the scattering of the resulting spray of particles. From that data they were able to isolate the contribution to the asymmetry of the scattering from the quarks. Although the uncertainty of the result was large, it was in line with the standard model prediction. The researchers hope to repeat the experiment to increase the sensitivity significantly.