New MIT detector will aid dark matter search

December 11, 2008

CAMBRIDGE, Mass.--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.
-end-
The research is partly funded by the National Science Foundation.

Written by David Chandler, MIT News Office

Massachusetts Institute of Technology

Related Dark Matter Articles from Brightsurf:

Dark matter from the depths of the universe
Cataclysmic astrophysical events such as black hole mergers could release energy in unexpected forms.

Seeing dark matter in a new light
A small team of astronomers have found a new way to 'see' the elusive dark matter haloes that surround galaxies, with a new technique 10 times more precise than the previous-best method.

Holding up a mirror to a dark matter discrepancy
The universe's funhouse mirrors are revealing a difference between how dark matter behaves in theory and how it appears to act in reality.

Zooming in on dark matter
Cosmologists have zoomed in on the smallest clumps of dark matter in a virtual universe - which could help us to find the real thing in space.

Looking for dark matter with the universe's coldest material
A study in PRL reports on how researchers at ICFO have built a spinor BEC comagnetometer, an instrument for studying the axion, a hypothetical particle that may explain the mystery of dark matter.

Looking for dark matter
Dark matter is thought to exist as 'clumps' of tiny particles that pass through the earth, temporarily perturbing some fundamental constants.

New technique looks for dark matter traces in dark places
A new study by scientists at Lawrence Berkeley National Laboratory, UC Berkeley, and the University of Michigan -- published today in the journal Science - concludes that a possible dark matter-related explanation for a mysterious light signature in space is largely ruled out.

Researchers look for dark matter close to home
Eighty-five percent of the universe is composed of dark matter, but we don't know what, exactly, it is.

Galaxy formation simulated without dark matter
For the first time, researchers from the universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter.

Taking the temperature of dark matter
Warm, cold, just right? Physicists at UC Davis are using gravitational lensing to take the temperature of dark matter, the mysterious substance that makes up about a quarter of our universe.

Read More: Dark Matter News and Dark Matter Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.