WEST LAFAYETTE — Results of the XENON100 experiment are a bright spot in the search for dark matter.
The team of international scientists involved in the project demonstrated the sensitivity of their detector and recorded results that challenge several dark matter models and a longstanding claim of dark matter detection. Papers detailing the results will be published in upcoming issues of the journals Science and Physical Review Letters.
Dark matter is an abundant but unseen matter in the universe considered responsible for the gravitational force that keeps the Milky Way galaxy together, said Rafael Lang, an assistant professor of physics at Purdue University who was involved in the research.
“Our galaxy spins like an incredibly fast merry-go-round, and the stars, planets and other objects would go flying off in different directions if it wasn't for gravitational pull,” he said. “When we calculate the gravity of every known mass, it is nowhere near enough force to keep the galaxy together. Dark matter is the stuff that makes up the difference.”
Although the team did not detect dark matter, the capabilities demonstrated by the XENON100 detector are encouraging. The high sensitivity shown in the experimental results could free the international research team from the need to constrain analysis to only a portion of the data captured, Lang said.
“Imagine the search for a very weak and elusive dark matter signal within many events from various sources of background,” Lang said. “It's like looking for a needle in a haystack. While most experiments have a huge pile of hay, our detector is so sharp and the background is so low, that our haystack is small and we can easily look at every piece of hay. We don't have to pick and choose what portion of the data we evaluate; we can look at every event. This opens the door for us to find evidence of dark matter in an unexpected place or in a form we didn't consider, which is good because no one yet knows what exactly dark matter is.”
Scientists from a dark matter project named Dark Matter Large Sodium Iodide Bulk for Rare Processes, and referred to as the DAMA/LIBRA project, claimed to have detected dark matter in 1998. The team observed a signal that varied with the seasons, as is expected for dark matter as the Earth's orbit around the sun changes the speed at which it passes through a halo of dark matter that envelops the Milky Way, Lang said.
However, other teams searching for dark matter did not observe the same signal. The DAMA/LIBRA team suggested that other groups could be blind to the signal because the dark matter was interacting with the atoms of the detector in an unexpected way. It was suggested that the dark matter could be leptophilic, meaning it prefers to interact with electrons, he said.
