Featured Research

from universities, journals, and other organizations

How strong is the weak force? New measurement of the muon lifetime

Date:
January 27, 2011
Source:
Paul Scherrer Institut (PSI)
Summary:
A new measurement of the muon lifetime - the most precise determination of any lifetime - provides a high-accuracy value for a crucial parameter determining the strength of weak nuclear force.

PSI scientist Bernhard Lauss with the detector array used in the determination of the muon lifetime.
Credit: PSI/F. Reiser

A new measurement of the muon lifetime -- the most precise determination of any lifetime -- provides a high-accuracy value for a crucial parameter determining the strength of weak nuclear force. The experiments were performed by an international research team at the accelerator facility of the Paul Scherrer Institute.

The results are about to be published in the journal Physical Review Letters.

The weak force is one of the four fundamental forces of Nature. Although we hardly encounter processes governed by the weak force in our everyday life, it is still of crucial importance; e.g., being responsible for the processes that make the Sun shine. An international research team led by scientists from the University of Illinois and Boston University performed experiments at the Paul Scherrer Institute (Villigen, Switzerland) that allowed them to determine a parameter crucial for the strength of the weak force with unprecedented accuracy of 0.6 parts per million. This so called Fermi constant is one of the fundamental natural constants needed for exact calculations of processes in the world of elementary particles.

One of the main breakthroughs in our understanding of the subatomic world in the 1970s was the proof that the weak interaction and the electromagnetic interaction -- another of the four fundamental forces -- are, in fact, two aspects of one and the same interaction. It is called the electroweak interaction and its strength is determined by three parameters, the Fermi constant being one of them.

Muon lifetime -- key to the strength of the weak force

The new value of the Fermi constant has been determined via an extremely precise determination of the lifetime of the muon -- the most precise measurement of the lifetime of any state in the atomic and subatomic world. The muon is an unstable subatomic particle decaying with a lifetime of approx. 2 microseconds (millionth 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, at the time of the experiment at the University of Illinois, now at the University of Washington "Since 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 2 millionths of a millionth of a second

The MuLan (Muon Lifetime Analysis) experiment used muons produced at the proton accelerator of the Paul Scherrer Institute (Villigen, Switzerland) -- 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 arriving positively charged muons during a "muon fill period." explains Bernhard Lauss from the Paul Scherrer Institute "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."

Robert Carey from Boston University adds: "We repeated this procedure for 100 billion muon fills, accumulating trillions of individual decays, which in turn required more than 100 TBytes of data to be stored for later analysis using the large supercomputer cluster at 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 fit to determine the mean lifetime, obtaining the value of 2.1969803 0.0000022 microseconds. The uncertainty is approximately 2 millionths of a millionth of a second -- a real world record.

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 USA; Department of Physics and Astronomy, University of Kentucky, Lexington, USA; Department of Physics, Boston University, Boston, USA; Department of Physics, James Madison University, Harrisonburg, USA; Department of Physics and Computational Science, Regis University, Denver, USA; Department of Mathematics and Physics, Kentucky Wesleyan College, Owensboro, USA; Paul Scherrer Institute, Villigen PSI, Switzerland; and Kernfysisch Versneller Instituut, University of Groningen, Groningen, The Netherlands.


Story Source:

The above story is based on materials provided by Paul Scherrer Institut (PSI). Note: Materials may be edited for content and length.


Journal Reference:

  1. D.M.Webber et al. Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision. Physical Review Letters, (in press)

Cite This Page:

Paul Scherrer Institut (PSI). "How strong is the weak force? New measurement of the muon lifetime." ScienceDaily. ScienceDaily, 27 January 2011. <www.sciencedaily.com/releases/2011/01/110125131450.htm>.
Paul Scherrer Institut (PSI). (2011, January 27). How strong is the weak force? New measurement of the muon lifetime. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2011/01/110125131450.htm
Paul Scherrer Institut (PSI). "How strong is the weak force? New measurement of the muon lifetime." ScienceDaily. www.sciencedaily.com/releases/2011/01/110125131450.htm (accessed July 23, 2014).

Share This




More Matter & Energy News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
Powered by NewsLook.com
Europe's Car Market on the Rebound?

Europe's Car Market on the Rebound?

Reuters - Business Video Online (July 23, 2014) Daimler kicks off a round of second-quarter earnings results from Europe's top carmakers with a healthy set of numbers - prompting hopes that stronger sales in Europe will counter weakness in emerging markets. Hayley Platt reports. Video provided by Reuters
Powered by NewsLook.com
9/11 Commission Members Warn of Terror "fatigue" Among American Public

9/11 Commission Members Warn of Terror "fatigue" Among American Public

Reuters - US Online Video (July 22, 2014) Ten years after releasing its initial report, members of the 9/11 Commission warn of the "waning sense of urgency" in combating terrorists attacks. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) 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