New detector will aid dark matter search

December 12, 2008

Several research projects are underway to try to detect particles that may make up the mysterious "dark matter" believed to dominate the universe's mass. But the existing detectors have a problem: They also pick up particles of ordinary matter -- hurtling neutrons that masquerade as the elusive dark-matter particles the instruments are designed to find.

MIT physicist Jocelyn Monroe has a solution. A new detector she and her students have built just finished its initial testing last week at Los Alamos National Laboratory. When deployed in the next few months alongside one of the existing dark-matter detectors, the new device should identify all of the ordinary neutrons that come along, leaving anything else that the other detector picks up as a strong candidate for the elusive dark matter.

"Dark matter experiments are very hard," explains Monroe, who worked on the project with undergraduates Dianna Cowern and Rick Eyers and with graduate students Shawn Henderson and Asher Kaboth. "They are looking for a tiny signal, from a phenomenon that happens very rarely," namely the collision of a dark-matter particle with one of ordinary matter, producing a tiny, brief flash of light.

Such flashes can be detected by putting a tank of liquid deep underground to shield it from most stray particles, then lining the tank with photomultiplier tubes that can pick up even the faintest bursts of light.

The problem is, even buried a mile underground, calculations show such detectors will pick up far more collisions from particles of ordinary matter than from those made of the still-unknown particles of dark matter. To be precise, the ordinary collisions should happen about 10 billion billion times (19 orders of magnitude) more often than the dark-matter collisions. So learning how to rule out those ordinary collisions is the key to finding the unknown matter.

"We're really trying to characterize the background," Monroe explains. "We're making a precise measurement of the energy spectrum of the neutron background." By understanding the nature and intensity of this background, it will be possible to design more effective shielding material to keep them away from the detectors.

And by running the two detectors at the same time, anytime a signal is seen in the neutron detector, any signal seen simultaneously in the dark-matter detector can be safely ignored. Only when the dark matter detector sees something and the neutron detector doesn't will there be a chance that one of the elusive dark-matter particles has been found.

Nobody knows what the dark matter is made of, but astronomers are sure it's there because of the way its gravitational attraction pulls on other, visible matter in space. That allows them to determine just how much of the mystery matter is out there -- more than five times as much as the amount of ordinary matter -- but not what it's made of.

Theorists have come up with a variety of candidates, but the leading contenders are a class of subatomic particles known as WIMPS -- weakly-interacting massive particles. These are the types of particles, including one called the neutralino, which should be detectable by the deep underground experiments.

"I think probably in the next five years, someone will see a candidate" for a dark-matter particle, Monroe says. Although some experiments have already claimed to see possible evidence of dark matter, so far those claimed results "are surprising and unconfirmed," Monroe says, and have not been accepted by most scientists.

To test the new detector, Monroe and her students took it to Los Alamos National Laboratory, where it was exposed to a neutron source so that its sensitivity could be precisely calibrated. Once the analysis of that test is completed, the device will be sent out to an underground laboratory, most likely at the planned Deep Underground Science and Engineering Laboratory. This facility, though not funded yet, would be set up in the Homestake Mine, a very deep old gold mining complex in South Dakota, and one of its multidisciplinary goals is provide the world's deepest location for the detection of cosmic dark matter.

The research is partly funded by the National Science Foundation.

Massachusetts Institute of Technology

---

---

	Dark Matter by Michelle Paver (Author) January 1937. Clouds of war are gathering over a fogbound London. Twenty-eight year old Jack is poor, lonely and desperate to change his life. So when he's offered the chance to join an Arctic expedition, he jumps at it. Spirits are high as the ship leaves Norway: five men and eight huskies, crossing the Barents Sea by the light of the midnight sun. At last they reach the remote, uninhabited bay where they will camp for the next year. Gruhuken. But the Arctic summer is brief. As night returns to claim the land, Jack feels a creeping unease. One by one, his companions are forced to leave. He faces a stark choice. Stay or go. Soon he will see the last of the sun, as the polar night engulfs the camp in months of darkness. Soon he will reach the point of no return - when the sea will...
	Dark Matter by S. W. Ahmed (Author) Dark matter, the invisible substance that constitutes the bulk of all matter in the universe, remains one of science's greatest mysteries. But what if it actually is nothing more than ordinary matter purposely hidden from our view? What if we are only allowed to see a small fraction of the stars in our galaxy, because the vast majority of star systems are teeming with aliens who wish to remain unseen? Marc Zemin, a brilliant student of astrophysics, is the first human to ever stumble upon this startling secret, when his experiments with wormhole travel cause aliens to land on Earth and whisk him away into space. To his astonishment, the aliens want his help in fighting a colossal galactic war that is rapidly spiraling out of control. But as he struggles to survive from battle to battle...
	The 4 Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality by Richard Panek (Author) “Fascinating . . . One of the most important stories in the history of science.”— Washington Post In recent years, a handful of scientists has been racing to explain a disturbing aspect of our universe: only 4 percent of it consists of the matter that makes up you, me, and every star and planet. The rest is completely unknown. Richard Panek tells the dramatic story of how scientists reached this cosmos-shattering conclusion. In vivid detail, he narrates the quest to find the “dark” matter and an even more bizarre substance called dark energy that make up 96 percent of the universe. This is perhaps the greatest mystery in all of science, and solving it will bring fame, funding, and certainly a Nobel Prize. Based on hundreds of interviews and in-depth, on-site reporting,...
	Dark Matter: A Century of Speculative Fiction from the African Diaspora by Sheree Renée Thomas (Editor) This volume introduces black science fiction, fantasy, and speculative fiction writers to the generations of readers who have not had the chance to explore the scope and diversity among African-American writers.
	Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos by Iain Nicolson (Author) Once we thought the universe was filled with shining stars, dust, planets, and galaxies. We now know that more than 98 percent of all matter in the universe is dark. It emits absolutely nothing yet bends space and time; keeps stars speeding around galaxies; and determines the fate of the universe. But dark matter is only part of the story. Scientists have recently discovered that the expansion of the universe is speeding up, driven by a mysterious commodity called dark energy. Depending on what dark matter and energy happen to be, our seemingly quiet universe could end its days in a Big Rip, tearing itself apart, or a Big Crunch, collapsing down to a universe the size of nothing, ready to be reincarnated in a Big Bang once again.For the general reader and armchair astronomer alike, Iain...
	Einstein's Telescope: The Hunt for Dark Matter and Dark Energy in the Universe by Evalyn Gates (Author) “Splendidly satisfying reading, designed for a nonspecialist audience.”—Kirkus Reviews, starred reviewEvalyn Gates, a talented astrophysicist, transports readers to the edge of contemporary science to explore the revolutionary tool—”Einstein’s telescope”—that is unlocking the secrets of the Universe. Einstein’s telescope, or gravitational lensing, is so-called for the way gravity causes space to distort and allow massive objects to act like “lenses,” amplifying and distorting the images of objects behind them. By allowing for the detection of mass where no light is found, scientists can map out the distribution of dark matter and come a step closer to teasing out the effects of dark energy on the Universe—which may forever upend long-held notions about where the...
	A Dark Matter by Peter Straub (Author) On a Midwestern campus in the 1960s, a charismatic guru and his young acolytes perform a secret ritual in a local meadow.  What happens is a mystery—all that remains is a gruesomely dismembered body and the shattered souls of all who were present.  Forty years later, one man seeks to learn about that horrifying night, and to do so he’ll have to force those involved to examine the unspeakable events that have haunted them ever since. Unfolding through their individual stories, A Dark Matter is an electric, chilling, and unpredictable novel that proves Peter Straub to be the master of modern horror.
	Dark Matter: The Private Life of Sir Isaac Newton: A Novel by Philip Kerr (Author) In 1696, Christopher Ellis, a young, hot-tempered gentleman, is sent to the Tower of London, but not as a prisoner. A sudden twist of fate has led him there to assist the renowned scientist Sir Isaac Newton, who as Warden of the Royal Mint has accepted an appointment to hunt down counterfeiters who threaten to topple the shaky, war-weakened economy. Armed with Newton’s superior intellect and Ellis’s skill with a sword, the new partners seem primed to solve the case. But when their investigation leads them to a mysterious coded message on a corpse hidden in the Lion Tower, they realize that something more sinister is afoot. In the heat of their pursuit, Newton and Ellis’s suspicions become all too real as the body count rises and the duo uncovers a menacing far-reaching plot that...
	Dark Matter: Art and Politics in the Age of Enterprise Culture (Marxism and Culture) by Gregory Sholette (Author) Art is big business, with some artists able to command huge sums of money for their works, while the vast majority are ignored or dismissed by critics. This book shows that these marginalized artists, the "dark matter" of the art world, are essential to the survival of the mainstream and that they frequently organize in opposition to it. Gregory Sholette, a politically engaged artist, argues that imagination and creativity in the art world originate thrive in the non-commercial sector shut off from prestigious galleries and champagne receptions. This broader creative culture feeds the mainstream with new forms and styles that can be commodified and used to sustain the few artists admitted into the elite. This dependency, and the advent of inexpensive communication, audio...
	Dark Matter, Dark Energy, Dark Gravity by FeedBrewer, Inc. Enabling a Universe that Supports Intelligent Life How did the profound beauty of our Earth, our Solar System, our Milky Way galaxy and indeed our universe unfold? Dark matter, dark energy, and dark gravity have made all the difference in how the universe has developed, and have been key to creating the overall environment that makes life possible. This book provides insight into what we know and what we hope to learn about dark matter, dark energy, and dark gravity. Each appears to play an essential role in the existence of a universe with characteristics like ours. We are immersed in a sea of light emanating from ordinary matter that is floating, as it were, on an ocean of dark matter. The dark matter itself floats on the dark energy of the particle...