The Jefferson Lab Free-Electron Laser was used by Rox Anderson’s group from the Wellman Center at Massachussetts General Hospital, part of Harvard Medical School, for a series of experiments aimed at curing acne, a debilitating disease of over-active sebaceous glands. Currently the drug Accutane® (generically called isotretinion) is used to treat acne, but its side effects can be worse than the disease.
Most known particles have either 3 quarks (baryons) or a quark-antiquark pair (mesons). The pentaquark is defined as a subatomic particle consisting of 4 quarks and one antiquark. If the pentaquark exists, then it would be a breakthrough in our understanding of how quarks can be put together to form composite particles. However, while there were claims by several experiments around the world for a pentaquark (now called the Θ+), newer, higher-statistics experiments put in doubt some of the earlier data claiming evidence for the Θ+.
While the proton is most simply described as a bound state of three quarks (2 up and 1 down), a more complete description includes a sea of gluons and virtual quark/anti-qu
The nucleus can often be approximated as an independent collection of protons and neutrons confined in a volume, but for short periods of time, the nucleons in the nucleus can strongly overlap. This quantum mechanical overlapping, known as a nucleon-nucleon short-range correlation, is a manifestation of the nuclear strong force, which produces not only the long-range attraction that holds matter together, but also the short-range repulsion that keeps it from collapsing.
Improved technology for originating CEBAF's electron beam enables nuclear physics experimenters to gather better data more efficiently. CEBAF's injector originates the electron beam, establishes its special characteristics, and then injects it into the accelerator. Over time, as CEBAF experiments generate new knowledge, nuclear physics researchers need to interrogate nature itself ever more deeply — which means they need increasingly exacting characteristics in the beam. That makes injector advances important.
Dedicated positron emission mammography (PEM) systems potentially provide a high sensitivity, high resolution alternative to whole body PET for positron breast imaging. In collaboration with Duke University Medical Center (Tim Turkington, PI), we have designed, built and evaluated a large field of view (15 cm x 20 cm) PEM system. The device is built with a set of two pixellated LGSO/LYSO crystal scintillators coupled to arrays of compact position sensitive photomultiplier tubes.
The Q2 dependence of the charge form factor of the neutron, GEn, can provide vital information on the origin of charge distribution in the neutron. A precise determination of GEn has challenged physicists for more than 40 years, primarily from the lack of a free neutron target and the fact that the charge form factor is so small.
Researchers demonstrate a new technique for producing polarized positrons that could improve manufacturing and lead to new discoveries.
The Science
When an energetic electron beam strikes matter, it produces photons, or packets of light, that can further convert their energy into pairs of an electron and a positron, the anti-particle twin to the electron. Researchers demonstrated that if the original electron beam is polarized (electrons “spin” in one direction), this polarization can be transferred to the positrons with nearly 100 percent efficiency.
