Featured Research

from universities, journals, and other organizations

Weak Interaction Helps Locate Strange Quark In Proton Structure

Date:
February 4, 2000
Source:
University Of Illinois At Urbana-Champaign
Summary:
Since Otto Stern first surprised his colleagues in 1933 by announcing that the proton magnetic moment was three times larger than expected, physicists have puzzled over the origin of the difference. During the past two summers the SAMPLE experiment at the MIT-Bates Linear Accelerator Center has shed new light on this question by measuring the proton magnetic moment as seen by the weak interaction, rather than the electromagnetic interaction.

CHAMPAIGN, Ill. -- Since Otto Stern first surprised his colleagues in 1933 by announcing that the proton magnetic moment was three times larger than expected, physicists have puzzled over the origin of the difference. During the past two summers the SAMPLE experiment at the MIT-Bates Linear Accelerator Center has shed new light on this question by measuring the proton magnetic moment as seen by the weak interaction, rather than the electromagnetic interaction.

Related Articles


"The new measurements provide information about how the different flavors of quarks in the proton generate the magnetic moment," said Doug Beck, a physics professor at the University of Illinois and a collaborator on SAMPLE. "Because the electromagnetic and weak interactions are very precisely related in the Standard Model of particle physics, the new experimental result can be combined with the ordinary proton magnetic moment to uncover the contributions of the up, down and strange quarks."

In the SAMPLE experiment, an intense beam of polarized electrons is scattered off a liquid hydrogen target. The backward-scattered electrons are detected with a Cerenkov detector. Because the counting rate must be very high to accumulate the necessary statistics for a part-per-million measurement, the detector signals are integrated rather than counted.

"The electrons are polarized so their spins are aligned either parallel or anti-parallel to the beam direction," Beck said. "Scattering experiments with these two types of beams are mirror images of each other and are therefore sensitive to the parity-violating nature of the weak interaction." It is the strange quark contribution to the magnetic moment that is of greatest interest because any such effects must come from the virtual quark-antiquark "sea" in the proton, Beck said. The effects of the sea on "large scale" proton properties such as the magnetic moment are largely unknown. In the first SAMPLE experiment, the parity-violating asymmetry of the proton was measured. "Using a theoretical estimate for the contribution of the weak interaction axial current, the portion of the magnetic moment due to strange quarks comes out to be significantly positive, contrary to most theoretical models," Beck said. The SAMPLE experimenters announced their most recent findings in the Jan. 31 issue of Physical Review Letters.

"In order to check the axial current contribution, a second measurement was made this summer using a deuterium target, where the strange quark effects from the proton and neutron are expected to largely cancel," Beck said. "Upon completion of the analysis of these data, the strange quark contribution to the proton magnetic moment should be cleanly determined."

The SAMPLE experiment is a collaboration between the U. of I., California Institute of Technology, Louisiana Tech University, University of Maryland, Massachusetts Institute of Technology, College of William and Mary, and Virginia Polytechnic Institute and State University.


Story Source:

The above story is based on materials provided by University Of Illinois At Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University Of Illinois At Urbana-Champaign. "Weak Interaction Helps Locate Strange Quark In Proton Structure." ScienceDaily. ScienceDaily, 4 February 2000. <www.sciencedaily.com/releases/2000/02/000204073943.htm>.
University Of Illinois At Urbana-Champaign. (2000, February 4). Weak Interaction Helps Locate Strange Quark In Proton Structure. ScienceDaily. Retrieved December 21, 2014 from www.sciencedaily.com/releases/2000/02/000204073943.htm
University Of Illinois At Urbana-Champaign. "Weak Interaction Helps Locate Strange Quark In Proton Structure." ScienceDaily. www.sciencedaily.com/releases/2000/02/000204073943.htm (accessed December 21, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Sunday, December 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Building Google Into Cars

Building Google Into Cars

Reuters - Business Video Online (Dec. 19, 2014) Google's next Android version could become the standard that'll power your vehicle's entertainment and navigation features, Reuters has learned. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
AP Review: Nikon D750 and GoPro Hero 4

AP Review: Nikon D750 and GoPro Hero 4

AP (Dec. 19, 2014) What to buy an experienced photographer or video shooter? There is some strong gear on the market from Nikon and GoPro. The AP's Ron Harris takes a closer look. (Dec. 19) Video provided by AP
Powered by NewsLook.com
Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Buzz60 (Dec. 19, 2014) A double-amputee makes history by becoming the first person to wear and operate two prosthetic arms using only his mind. Jen Markham has the story. Video provided by Buzz60
Powered by NewsLook.com
Navy Unveils Robot Fish

Navy Unveils Robot Fish

Reuters - Light News Video Online (Dec. 18, 2014) The U.S. Navy unveils an underwater device that mimics the movement of a fish. Tara Cleary reports. Video provided by Reuters
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