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 Airborne thermometer to measure Arctic temperatures
11.01.2017 | Moscow Institute of Physics and Technology

nachricht Next-generation optics offer the widest real-time views of vast regions of the sun
11.01.2017 | New Jersey Institute of Technology

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: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Energy-Efficient Building Operation: Monitoring Platform MONDAS Identifies Energy-Saving Potential

16.01.2017 | Trade Fair News

Designing Architecture with Solar Building Envelopes

16.01.2017 | Architecture and Construction

Sensory Stimuli Control Dopamine in the Brain

13.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>