BLOGS

At a press conference February 17 during the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston, Samuel Ting, the MIT physicist who is the principal investigator for AMS, said his team was working on a paper analyzing a subset of the AMS data involving detections of high-energy electrons and positrons. “We waited for 15 years—actually, 18 years—to write this paper,” he said. “We have finished the paper and are now making the final checks.” He said he anticipated that the paper would be completed and submitted to a journal (as yet undecided, although Ting said later one possibility is Physical Review Letters) in two to three weeks.

While Ting didn’t disclose any of the results that will be in that paper, he did discuss what the paper would cover. It will examine the ratio of positrons to electrons as a function of energy from 0.5 to 350 billion electron volts. (The AMS can detect particles up to a trillion electron volts, but Ting said they didn’t yet have a statistically significant sample of data at the higher energies.) It will also measure changes in the ratio as a function of direction to see if its distribution is the same in all directions or has peaks in a particular direction, such as towards the center of the galaxy.

Changes in that positron/electron ratio as a function of energy, including increases or sharp drops, could provide evidence for one candidate of dark matter known as weakly interacting massive particles, or WIMPs. Dark matter comprises about 23 percent of the universe, but its influence has only been detected indirectly, such as the rotation curves of galaxies. Scientists hypothesize that if dark matter is made of WIMPS—in particular, a particle known as a supersymmetric neutralino—it will produce antimatter particles like positrons when it collides with each other, creating a signature in the data detected by AMS.