Featured Research

from universities, journals, and other organizations

Physicists set strongest limit on mass of dark matter

Date:
November 24, 2011
Source:
Brown University
Summary:
Physicists have set the strongest limit for the mass of dark matter, the mysterious particles believed to make up nearly a quarter of the universe. The researchers report that dark matter must have a mass greater than 40 giga-electron volts. The distinction is important because it casts doubt on recent results from underground experiments that have reported detecting dark matter.

View of the universe from NASA's Fermi Gamma-ray Space Telescope Brown physicists studied seven dwarf galaxies, circled in white (click to enlarge). Observations indicate the dwarf galaxies are full of dark matter because their stars’ motion cannot be fully explained by their mass alone, making them ideal places to search for dark matter annihilation signals.
Credit: Koushiappas and Geringer-Sameth/Brown University

Brown University physicists have set the strongest limit for the mass of dark matter, the mysterious particles believed to make up nearly a quarter of the universe. The researchers report in Physical Review Letters that dark matter must have a mass greater than 40 giga-electron volts. The distinction is important because it casts doubt on recent results from underground experiments that have reported detecting dark matter.

If dark matter exists in the universe, scientists now have set the strongest limit to date on its mass.

In a paper to be published on Dec. 1 in Physical Review Letters, Brown University assistant professor Savvas Koushiappas and graduate student Alex Geringer-Sameth report that dark matter must have a mass greater than 40 giga-electron volts in dark-matter collisions involving heavy quarks. (The masses of elementary particles are regularly expressed in term of electron volts.) Using publicly available data collected from an instrument on NASA's Fermi Gamma-ray Space Telescope and a novel statistical approach, the Brown pair constrained the mass of dark matter particles by calculating the rate at which the particles are thought to cancel each other out in galaxies that orbit the Milky Way galaxy.

"What we find is if a particle's mass is less than 40 GeV, then it cannot be the dark matter particle," Koushiappas said.

The observational measurements are important because they cast doubt on recent results from dark matter collaborations that have reported detecting the elusive particle in underground experiments. Those collaborations -- DAMA/LIBRA, CoGeNT and CRESST -- say they found dark matter with masses ranging from 7 to 12 GeV, less than the limit determined by the Brown physicists.

"If for the sake of argument a dark matter particle's mass is less than 40 GeV, it means the amount of dark matter in the universe today would be so much that the universe would not be expanding at the accelerated rate we observe," Koushiappas said, referring to the 2011 Nobel prize in physics that was awarded for the discovery that the expansion of the universe is accelerating.

The Fermi-LAT Collaboration, an international scientific collaboration, arrived at similar results, using a different methodology. The Brown and Fermi-LAT collaboration papers will be published in the same issue of Physical Review Letters.

Physicists believe everything that can be seen -- planets, stars, galaxies and all else -- makes up only 4 percent of the universe. Observations indicate that dark matter accounts for about 23 percent of the universe, while the remaining part is made up of dark energy, the force believed to cause the universe's accelerated expansion. The problem is dark matter and dark energy do not emit electromagnetic radiation like stars and planets; they can be "seen" only through their gravitational effects. Its shadowy profile and its heavy mass are the main reasons why dark matter is suspected to be a weakly interacting massive particle (WIMP), which makes it very difficult to study.

What physicists do know is that when a WIMP and its anti-particle collide in a process known as annihilation, the debris spewed forth is composed of heavy quarks and leptons. Physicists also know that when a quark and its anti-quark sibling annihilate, they produce a jet of particles that includes photons, or light.

Koushiappas and Geringer-Sameth in essence reversed the annihilation chain reaction. They set their sights on seven dwarf galaxies which observations show are full of dark matter because their stars' motion cannot be fully explained by their mass alone. These dwarf galaxies also are largely bereft of hydrogen gas and other common matter, meaning they offer a blank canvas to better observe dark matter and its effects. "There's a high signal-to-noise ratio. They're clean systems," Koushiappas said.

The pair analyzed gamma ray data collected over the last three years by the Fermi telescope to measure the number of photons in the dwarf galaxies. From the number of photons, the Brown researchers were able to determine the rate of quark production, which, in turn, allowed them to establish constraints on the mass of dark matter particles and the rate at which they annihilate.

"This is the first time that we can exclude generic WIMP particles that could account for the abundance of dark matter in the universe," Koushiappas said.

Geringer-Sameth developed the statistical framework to analyze the data and then applied it to observations of the dwarf galaxies. "This is a very exciting time in the dark matter search, because many experimental tools are finally catching up to long-standing theories about what dark matter actually is," said Geringer-Sameth, from Croton-on-Hudson, N.Y. "We are starting to really put these theories to the test."

The National Science Foundation funded the research.


Story Source:

The above story is based on materials provided by Brown University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Alex Geringer-Sameth and Savvas M. Koushiappas. Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with data from the Fermi Gamma-ray Space Telescope. Physical Review Letters, Dec. 1, 2011 [link]

Cite This Page:

Brown University. "Physicists set strongest limit on mass of dark matter." ScienceDaily. ScienceDaily, 24 November 2011. <www.sciencedaily.com/releases/2011/11/111123133626.htm>.
Brown University. (2011, November 24). Physicists set strongest limit on mass of dark matter. ScienceDaily. Retrieved September 19, 2014 from www.sciencedaily.com/releases/2011/11/111123133626.htm
Brown University. "Physicists set strongest limit on mass of dark matter." ScienceDaily. www.sciencedaily.com/releases/2011/11/111123133626.htm (accessed September 19, 2014).

Share This



More Space & Time News

Friday, September 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Boeing, SpaceX to Send Astronauts to Space Station

Boeing, SpaceX to Send Astronauts to Space Station

AFP (Sep. 17, 2014) — NASA selected Boeing and SpaceX on Tuesday to build America's next spacecraft to carry astronauts to the International Space Station (ISS) by 2017, opening the way to a new chapter in human spaceflight. Duration: 01:13 Video provided by AFP
Powered by NewsLook.com
East Coast Treated To Rare Meteor Sighting

East Coast Treated To Rare Meteor Sighting

Newsy (Sep. 16, 2014) — Numerous residents along the East Coast reported seeing a bright meteor flash through the sky Sunday night. Video provided by Newsy
Powered by NewsLook.com
Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) — Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
NASA Picks Boeing and SpaceX to Ferry Astronauts

NASA Picks Boeing and SpaceX to Ferry Astronauts

AP (Sep. 16, 2014) — NASA is a giant step closer to launching Americans again from U.S. soil. It has announced it has picked Boeing and SpaceX to transport astronauts to the International Space Station in the next few years. (Sept. 16) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins