Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Zooming in on a proton packed with surprises

05.12.2003


The structure of the proton is under the microscope at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, Virginia, where a series of experiments continues to produce unexpected results.


The shape of the proton can differ, depending on the angular momentum of quarks.
(Gerald A. Miller/University of Washington)



Simple theories of proton structure say that the way electric charge is distributed in the proton is the same as the magnetization distribution. But Jefferson Lab results indicate these distributions are definitely different.

A fundamental goal of nuclear physics is to understand the structure and behavior of strongly interacting matter in terms of its building blocks, quarks and gluons. An important step toward this goal is a description of the internal structure for the proton and neutron, collectively known as nucleons. Jefferson Lab was built, in part, to study the physics of quarks and gluons and their connection to larger composite objects like protons.


The proton is the positively charged core of the hydrogen atom, the most abundant element in the universe. It is made up of three charged quarks and the gluons that bind them together. The quarks move around, so the proton has a charge distributed over its size. This leads to the generation of an electric current, which in turn induces a magnetic field. In addition, quarks and gluons both have spin, leading to a magnetic moment. The combination of the total magnetic field and the magnetic moment is a quantity called magnetization.

Jefferson Lab is uniquely positioned to measure the proton’s electric charge and magnetization distributions, the so-called electromagnetic form factors that describe its internal structure.

In two recent Jefferson Lab experiments, researchers directed the accelerator’s polarized electron beam toward liquid hydrogen cooled to 17 Kelvin (–429°F). Each electron in the beam has an intrinsic angular momentum, or spin. The beam of electrons is said to be "polarized" if their spins point — on average — in a specific direction. As an electron collided with a proton in the hydrogen target, the proton recoiled, becoming polarized during the interaction. The scattered electron and recoiling proton were then detected in two high-resolution spectrometers (HRS), and the proton polarization was measured by a specially developed detector called a proton polarimeter.

From these measurements, the researchers could obtain a ratio of electric charge distribution to magnetization distribution — the electric and magnetic form factors — at various depths inside the proton. Their experiments revealed unexpected and significantly different energy-dependence for the form factors. The data showed that the proton’s charge distribution is not the same as its magnetization distribution; the charge distribution is more spread out than the magnetization.

These results are very interesting to both experimental and theoretical physicists. The Jefferson Lab data has already had an impact on theoretical models, helping rule out some models, directing others toward a better description of internal proton structure.

One such model was developed in 1996 by physicists Gerald A. Miller and Michael R. Frank, both from the University of Washington in Seattle, and Byron K. Jennings from TRIUMF in Vancouver. The researchers predicted a fall-off in the ratio of the electromagnetic form factors but, at the time, they didn’t realize that experimental confirmation was possible. When the results of the first Jefferson Lab experiments probing proton structure were announced in 2000, the prediction was confirmed.

An interesting by-product of Miller’s theory is that the proton is not necessarily spherical in shape. Depending on the angular momentum of the quarks, the proton could be spherical in shape or more like a doughnut, a pretzel or a peanut. Miller says the variety of shapes is nearly limitless, and depends on the momentum of the quarks and the angle between the spin of the quark and the spin of the proton.

Media contact: Linda Ware, Jefferson Lab Public Affairs Manager, 757-268-7689, ware@jlab.org
Technical contacts: Vina Punjabi (punjabi@jlab.org); Charles Perdrisat (perdrisa@jlab.org)

Linda Ware | Jefferson Lab
Further information:
http://www.jlab.org/div_dept/dir_off/public_affairs/news_releases/2003/03protonshape.html

More articles from Physics and Astronomy:

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

nachricht NASA team finds noxious ice cloud on saturn's moon titan
19.10.2017 | NASA/Goddard Space Flight Center

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>