Featured Research

from universities, journals, and other organizations

Scientists Discover That Neutrinos Have Mass

Date:
June 5, 1998
Source:
Boston University
Summary:
A research team has found the first evidence that neutrinos--tiny electrically neutral sub-atomic particles--have mass. The finding may have significant implications in the debate over whether the universe has enough mass to halt, or even reverse, the outward expansion that began with the "Big Bang" and may lead to a unified explanation of the basic nature of the universe.

BOSTON, Mass.--A research team of scientists from the United States and Japan organized by physicists at Boston University, the University of California-Irvine, and the University of Tokyo, has found the first evidence that neutrinos--tiny electrically neutral sub-atomic particles--have mass.

This finding, which contradicts the standard theory of particle physics, may have significant implications in the debate over whether the universe has enough mass to halt, or even reverse, the outward expansion that began with the "Big Bang" and may lead to a unified explanation of the basic nature of the universe. Because of their negligible size and lack of charge, neutrinos can pass through the entire earth without interacting with matter, making them extremely difficult to detect.

"This finding means that we need to take a new look at the theoretical models of the structure of matter," says James Stone, professor of physics at Boston University and U.S. co-spokesperson for the project. "It sheds light on our basic questions about the nature of the universe, including the question the validity of the standard model of particle physics." The announcement was made June 4 at "Neutrino '98", an international physics conference underway in Takayama, Japan.

Many neutrinos are created when high energy cosmic rays bombard the earth's upper atmosphere producing cascades of secondary particles that rain down upon the earth. For this study scientists used the massive Super-Kamiokande detector, buried 1,000 meters underground at the Kamioka Mining and Smelting Company Mine in Mozumi, Japan. The tank, 40 meters in diameter, 40 meters high--the size of a nine story building--and weighing 50,000 tons, is filled with the world's purist water.

More than 13,000 cameras are mounted in the tank and used to detect the faint flashes of light produced as a secondary effect--like a sonic boom--of neutrinos moving through the water. The scientists used the information from the detector to count the neutrinos and classify them according to type, either electron- or muon-neutrino.

Based on our knowledge of cosmic rays, twice as many muon-neutrinos as electron neutrinos should be detected, and this should be true regardless of the direction of the source of the neutrinos. The Super Kamikande detected the expected number of electron-neutrinos--but only half the number of muon-neutrinos that were expected--among those that traveled a greater distance (through the earth from the opposite side of the globe). The scientists concluded that the missing muon-neutrinos had "oscillated" away, i.e., changed into undetectable tau-neutrinos or some other unknown type of neutrino as they traveled. According to Einstein, this transformation can occur only if the neutrinos possess mass. The experiment directly determines that the mass difference between the neutrinos is very small. The primary results have a statistical significance of more than 5 standard deviations. An independent measurement based on upward-going muons in the detector confirms the result.

The Super Kamiokande experiment is based on techniques pioneered by the Boston University and University of California-Irvine teams at a detector located in Cleveland, Ohio, which discovered neutrinos from a supernova in 1987, and the first indications of the oscillation of neutrinos a decade ago. The Super Kamiokande detector is seven times the size of the Ohio detector.

"The major problem in physics for the last quarter century has been the problem of mass--Where does it come from?" says Lawrence Sulak, an initiator of the first detector and principal investigator on the current project. "Until this observation neutrinos were thought to be massless. Now we know that we have not missed a fundamental symmetry of nature that forbids a neutrino mass. On the contrary, that neutrinos do have mass provides a critical clue in the unification of the particles and forces of nature."

Costs for this astrophysical observatory exceed $100 million, primarily provided by the Japanese Ministry of Education, Science, Sports, and Culture (Monbusho). Funding for the detector's outer region was provided by the United States Department of Energy. About 100 physicists from 23 institutions are participating in the project.

Since the beginning of its operation in April, 1996, the Super-Kamiokande experiment has been the most sensitive in the world for monitoring neutrinos from various sources. Neutrino oscillations have also been found in the measurements of electron-neutrinos coming from the sun. The number detected is about 35% of the number predicted by the well established theoretical model of the sun's neutrino producing processes. There has also been an indication that the observed energy spectrum of those neutrinos is different from the predicted one. These observations may also be interpreted as the result of oscillations.

Further information and images of the detector can be found at http://hep.bu.edu/~superk.


Story Source:

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


Cite This Page:

Boston University. "Scientists Discover That Neutrinos Have Mass." ScienceDaily. ScienceDaily, 5 June 1998. <www.sciencedaily.com/releases/1998/06/980605080658.htm>.
Boston University. (1998, June 5). Scientists Discover That Neutrinos Have Mass. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/1998/06/980605080658.htm
Boston University. "Scientists Discover That Neutrinos Have Mass." ScienceDaily. www.sciencedaily.com/releases/1998/06/980605080658.htm (accessed October 2, 2014).

Share This



More Matter & Energy News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Japan Looks To Faster Future As Bullet Train Turns 50

Japan Looks To Faster Future As Bullet Train Turns 50

Newsy (Oct. 1, 2014) Japan's bullet train turns 50 Wednesday. Here's a look at how it's changed over half a century — and the changes it's inspired globally. Video provided by Newsy
Powered by NewsLook.com
US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Raw: Japan Celebrates 'bullet Train' Anniversary

Raw: Japan Celebrates 'bullet Train' Anniversary

AP (Oct. 1, 2014) A ceremony marking 50 years since Japan launched its Shinkansen bullet train was held on Wednesday in Tokyo. The latest model can travel from Tokyo to Osaka, a distance of 319 miles, in two hours and 25 minutes. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Robotic Hair Restoration

Robotic Hair Restoration

Ivanhoe (Oct. 1, 2014) A new robotic procedure is changing the way we transplant hair. The ARTAS robot leaves no linear scarring and provides more natural results. Video provided by Ivanhoe
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:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

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