Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Physicists see golden needle in a micro-cosmic haystack

24.03.2004


An international team of physicists examining an extremely rare form of subatomic particle decay -- a veritable golden needle in a micro-cosmic haystack of 7.8 trillion candidates -- has discovered evidence for the highly sought process, which could be an indication of new forces beyond those incorporated in the Standard Model of particle physics. That long-standing theory of all particle physics precisely predicts the rate of such decays to be half that observed by the experimenters although it is still too soon to say if a deviation has occurred. The innovative experiment, which uses the most comprehensive particle detector ever built, is located at the U.S. Department of Energy’s Brookhaven National Laboratory. The result is being presented at a colloquium at Brookhaven Lab today and has been submitted to Physical Review Letters.



The experiment detects the disintegration of an unstable subatomic particle called a K meson, which can decay, or break apart, in a variety of ways. One particular decay -- in which the K meson turns into other particles, a positively charged pion, a neutrino, and an antineutrino -- is extremely important due to the internal subatomic processes involved and its sensitivity to new physical effects not accounted for in the Standard Model. The decay is so rare that it was predicted to happen only once in all the decays ever observed by all of the experiments that have searched for it since the 1960s.

The latest evidence of the long-sought process was found in just-analyzed data. It followed two earlier sightings at Brookhaven in 1997 and 2002 (see: http://www.bnl.gov/bnlweb/pubaf/pr/2002/bnlpr011002.htm). The new data were obtained using improved apparatus that exploited higher beam intensities and achieved greater efficiency of detection than any previous experimental setup.


The current result indicates that this particular rare K meson decay occurs once in every 7 billion decays. The improved result continues to suggest a possible discrepancy with the Standard Model, although with only 3 events, the result is still consistent with this model’s prediction of one in 13 billion decays.

"It is very important to establish whether these first few events represent a statistical fluke or an important breakthrough," said Douglas Bryman, Professor of Physics at the University of British Columbia, one of the experiment’s spokespersons. "This can only be done with an enhanced event sample, which could be obtained by further running of the experiment. "Additional running would resolve the issue and firmly establish whether we are seeing an extremely significant departure from standard theory," Bryman said. Such further running would require program funding not presently planned.

The long trek leading to discovery

The experimental collaboration -- now composed of 70 scientists from Canada, Japan, Russia and the United States, (see: http://www.phy.bnl.gov/E949/, Collaboration List) -- has been conducting the search for the past decade at the Alternating Gradient Synchrotron, a particle accelerator at Brookhaven Lab that produces the world’s most intense beams of K mesons. K mesons are elusive particles that exist for only 12 billionths of a second before decaying into other forms. So, to catch the fleeting events and identify the rare decay, the scientists built a state-of-the-art particle detector the size of a small house, capable of examining 1.6 million decays every second. Interesting events get recorded on tape, with several tens of thousands of gigabytes of data stored so far. The physicists then use sophisticated software to pore over the data to find the most interesting events and examine them in exquisite detail.

Although a neutrino and an antineutrino are also emitted in this K meson decay, these particles interact too weakly to be detected. Thus, evidence that one positive pion -- and only a positive pion -- was produced by the K meson decay must be proven beyond a reasonable doubt, eliminating the possibility that other detectable particles are present. To establish the validity of the observations, the scientists must reject all background cases where a K meson decays in other ways, usually involving a charged particle or a neutral pion. In order to achieve the unprecedented level of filtering required, the group developed the most efficient particle detector system ever built.

The hard part here is that neutral pions immediately decay into two high-energy gamma rays (photons), and the experiment must not miss them more than once in every million decays. To do this, the detector stops the K mesons in their tracks -- in a scintillating fiber target -- before they decay. The decay products then travel through a particle-tracking chamber surrounded by a huge magnet and plastic scintillation counters, so their momentum, trajectories, and energy can be precisely measured to positively identify the types of particles detected. Events that emit photons are picked up by sensitive detectors and rejected, leaving only the rarest decays as candidates for the process the scientists are seeking.

Out of all the data analyzed, the scientists have now seen three events explicable by the rare K meson decay they’ve been searching for. Their goal is to increase the experimental exposure by five times. If their findings continue at the current pace, 20 or more events would be observed. Such a result could profoundly alter our current picture of particle physics, forcing an expanded view of the fundamental constituents of the universe and their interactions since the ’Big Bang.’


This research was funded by the Office of High-Energy Physics within the Department of Energy’s Office of Science, with additional support from the Natural Sciences and Engineering Research Council and the National Research Council of Canada, and through agreements with the Japanese and Russian governments to support research at Department of Energy facilities.

For technical background, go to: http://www.phy.bnl.gov/E949/

If you’d like a PDF version of this press release using the scientific characters, contact: kmcnulty@bnl.gov.

One of the ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

Visit Brookhaven Lab’s electronic newsroom for links, news archives, graphics, and more: http://www.bnl.gov/newsroom

Karen McNulty Walsh | BNL
Further information:
http://www.bnl.gov/bnlweb/pubaf/pr/2004/bnlpr032304b.htm
http://www.bnl.gov/newsroom

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>