Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Measurement of the Muon Lifetime Provides Key to Determining Strength of Weak Nuclear Force

08.02.2011
After a decade of experimental development, data-taking, and analysis, an international research team led by scientists from Boston University and the University of Illinois has announced a new value for the muon lifetime.

The new lifetime measurement—the most precise ever made of any subatomic particle—makes possible a new determination of the strength of the weak nuclear force. Experiments for this research were conducted using the proton accelerator facility of the Paul Scherrer Institute (PSI) in Villigen, Switzerland. The results were published in the January 25, 2011 issue of the journal Physical Review Letters. *

How strong is the weak force?

The weak force is one of the four fundamental forces of nature. Although rarely encountered in everyday life, the weak force is at the heart of many elemental physical processes, including those responsible for making the sun shine. All four of the fundamental forces are characterized by coupling constants, which

describe their strength. The famous constant G, in Newton’s law of gravitation, determines the gravitational attraction between any two massive objects. The fine structure constant determines the strength of the electrostatic force between charged particles.

The coupling constant for the weak interactions, known as the Fermi constant, is also essential for calculations in the world of elementary particles. Today, physicists regard the weak and the electromagnetic interaction as two aspects of one and the same interaction. Proof of that relationship, established in the 1970s, was an important breakthrough in our understanding of the subatomic world.

Muon lifetime - key to the strength of the weak force

The new value of the Fermi constant was determined by an extremely precise measurement of the muon lifetime. The muon is an unstable subatomic particle which decays with a lifetime of approximately two microseconds (two millionths of a second). This decay is governed by the weak force only, and the muon's lifetime has a relatively simple relationship to the strength of the weak force. "To determine the Fermi constant from the muon lifetime requires elegant and precise theory, but until 1999, the theory was not as good as the experiments," says David Hertzog, professor of physics at the University of Washington. (At the time of the experiment, Hertzog was at the University of Illinois.) “Then, several breakthroughs essentially eliminated the theoretical uncertainty. The largest uncertainty in the Fermi constant determination was now based on how well the muon lifetime had been measured."

Measuring procedure repeated 100 billion times - precision of the measurement two millionths of a millionth of a second

The MuLan (Muon Lifetime Analysis) experiment used muons produced at PSI’s proton accelerator—the most powerful source of muons in the world and the only place where this kind of experiment can be done. "At the heart of the experiment were special targets that caught groups of positively charged muons during a ‘muon fill period,’" says PSI’s Bernhard Lauss. "The beam was then rapidly switched off, leaving approximately 20 muons in the target. Each muon would eventually decay, typically ejecting an energetic positron—a positively charged electron—to indicate its demise. The positrons were detected using a soccer-ball shaped array of 170 detectors, which surrounded the target." Boston University physics professor Robert Carey adds, "We repeated this procedure for 100 billion muon fills, accumulating trillions of individual decays. By the end, we had recorded more than 100 terabytes of data, far more than we could handle by ourselves. Instead, the data was stored and analyzed at the National Center for Supercomputing Applications (NCSA) in Illinois." A distribution of how long each muon lived before it decayed was created from the raw data and then fit to determine the mean lifetime: 2.1969803 ±0.0000022 microseconds. The uncertainty is approximately 2 millionths of a millionth of a second - a world record.

*D. M. Webber et al. (MuLan Collaboration), “Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision.” Physical Review Letters. 106, 041803 (2011) [5 pages]. An abstract of the article is available at http://prl.aps.org/abstract/PRL/v106/i4/e041803.

The collaboration

The experiments were performed at the Paul Scherrer Institute by an international collaboration including scientists from the following institutions:

Department of Physics
University of Illinois at Urbana-Champaign
Urbana, Illinois 61801, USA Department of Physics and Computational Science
Regis University
Denver, Colorado 80221, USA
Department of Physics and Astronomy
University of Kentucky
Lexington, Kentucky 40506, USA
Department of Mathematics and Physics
Kentucky Wesleyan College
Owensboro, Kentucky 42301, USA
Department of Physics
Boston University
Boston, Massachusetts 02215, USA
Paul Scherrer Institute
CH-5232 Villigen PSI, Switzerland
Department of Physics
James Madison University
Harrisonburg, Virginia 22807, USA KVI
University of Groningen
NL-9747AA Groningen, The Netherlands
About the Paul Scherrer Institute (PSI)—The PSI develops, builds and operates large-scale, complex research facilities, and makes these facilities available to the national and international research community. The Institute’s own research focuses on solid-state physics and the materials sciences, elementary particle physics, biology and medicine, as well as research involving energy and the environment. With a workforce of 1400 and an annual budget of about 300 million CHF, PSI is the largest research institution in Switzerland.

About Boston University—Founded in 1839, Boston University is an internationally recognized institution of higher education and research. With more than 30,000 students, it is the fourth largest independent university in the United States. BU contains 17 colleges and schools along with a number of multi-disciplinary centers and institutes which are central to the school's research and teaching mission.

Contacts

Prof. Robert Carey
Department of Physics
Boston University
590 Commonwealth Avenue
Boston, MA 02215, USA
Phone: +1 (617) 353 6031
E-mail: carey@bu.edu
Prof. David Hertzog
Department of Physics
University of Washington
Box 351560, Seattle, WA 98195-1560, USA
Phone: +1 (206) 543-0839
E-mail: hertzog@uw.edu
Dr. Bernhard Lauss
Laboratory for Particle Physics,
Paul Scherrer Institut,
CH-5232 Villigen PSI, Switzerland,
Phone: +41(0)56 310 46 47
E-mail: bernhard.lauss@psi.ch
For high-resolutions images related to this article, contact:
Dagmar Baroke, M.A.
Abteilungsleiterin Kommunikation
Paul Scherrer Institut
CH-5232 Villigen PSI
Tel: 056/310 29 16
Fax: 056/310 27 17
www.psi.ch

Patrick Farrell | Newswise Science News
Further information:
http://www.bu.edu

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

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: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>