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G-ZERO GROUP, INCLUDING CARNEGIE MELLON RESEARCHERS, FINDS STRANGE QUARKS INFLUENCE PROTON STRUCTURE
09 August 2006 - Carnegie Mellon Universtity

In research performed at the Department of Energy's Jefferson Lab in Newport News, Va., nuclear physicists, including a team from Carnegie Mellon University, have found that strange quarks do contribute to the structure of the proton.

This result indicates that, just as previous experiments have hinted, strange quarks in the proton's quark-gluon sea contribute to a proton's properties. The result comes from work performed by the G-Zero collaboration, an international group of 108 physicists from 19 institutions, presented today at a Jefferson Lab physics seminar.

Doug Beck, professor of physics at the University of Illinois at Urbana-Champaign and spokesperson for the G-Zero collaboration, is presenting the results at a public physics seminar titled "Strange Quark Contributions to Nucleon Structure? Results from the Forward G0 Experiment" at Jefferson Lab. A formal scientific paper is being submitted for review and publication.

A group of Carnegie Mellon researchers has been part of the G-Zero collaboration since its initiation in 1991. During that time, 10 Carnegie Mellon students working under physics professors Gregg B. Franklin and Brian Quinn have participated in the experiment. The university's Physics Department has a long-standing relationship with Jefferson Lab in conducting ground-breaking experiments in medium-energy physics and in constructing many pieces of equipment used in the research.

"This experiment takes us a step closer to understanding the basic building blocks of matter," said Franklin. "The mass of an atom comes from the protons and neutrons at its center. Protons and neutrons are, in turn, built from elementary particles called 'quarks.' This experiment tells us that the so-called 'strange-quark' plays a role in determining the properties of the proton."

Protons are found in the heart of all matter: the nucleus of the atom. Physicists have long known that protons are primarily built of quarks, along with particles called gluons that bind the quarks together. There are three permanent quarks in the proton that come in two "flavors": two "up" and one "down." Up and down quarks are the lightest of the possible six flavors of quarks that appear to exist in the universe.

In addition to the proton's three resident quarks, the peculiar rules of quantum mechanics allow other particles to appear from time to time. These ghostly particles usually vanish in a tiny fraction of a second, but it's possible that they stay around long enough to influence the structure of the proton. Nuclear physicists set out to catch some of these ghostly particles in the act. They determined that the next-lightest quark, the "strange" quark, would be the most likely to have a visible effect.

According to Beck, one way to see these strange quarks is to measure them through the weak interaction. "If we look with photons via the electromagnetic interaction, we see quarks inside the proton. And then, if we do it with the weak interaction, we see a very similar, yet distinctly different view of the quarks. And it's by comparing those pictures that we can get at the strange quark contribution," Beck said.

Since the hydrogen nucleus consists of a single proton, G-Zero researchers sent a polarized beam of electrons into a hydrogen target. They then watched to see how many protons were "scattered," essentially knocked out of the target, by the electrons. Throughout the experiment, the researchers alternated the electron beam's polarization (spin).

"We run the beam with polarization in one direction, and look to see how many protons are scattered. Then we turn the beam around, in polarization at least, and measure for exactly the same amount of time again and look to see how many protons are scattered. And there will be a different number by about 10 parts per million," Beck said. That's because the electromagnetic force is mirror-symmetric (the electrons' spin will not affect the number of protons scattered), while the weak force is not (electrons polarized one way will interact slightly differently than electrons spinning oppositely).

"The relative difference in those counting rates tells us how big the weak interaction piece is in this scattering of electrons from protons. We compare it to the strength of the electromagnetic interaction between electrons and protons, and that gives us the answer that we're looking for," Beck explained.

What the researchers found was that strange quarks do contribute to the structure of the proton. In particular, Beck said the collaboration found that strange quarks contribute to the proton's electric and magnetic fields, in other words, its charge distribution and magnetization.

"All quarks carry charge, and one of the things we measure is where the strange quarks are located in the proton's overall charge distribution," he explained. "And then there's a related effect. There are these charged quarks inside the protons, and they're moving around. And when charged objects move around, they can create a magnetic field. In G-Zero, we also measure how strange quarks contribute to the proton's magnetization."

G-Zero allowed the researchers to extract a quantity representing the strange quark's contribution to a combination of the proton's charge and magnetization. "The data indicate that the strange quark contributions are non-zero over the entire range of our measurements," Beck said, "And there are a couple of points that overlap other measurements. They agree, so that's a good thing."

However, by itself, the G-Zero result does not yet allow the researchers to separate the strange quark's contribution to the charge from its contribution to the magnetization. "There's another G-Zero run coming up in December, and that will help us to try to disentangle this combination of the contribution to the charge and the magnetization. So that will give us one more measurement that will allow us to look at those quantities separately," Beck added.

G-Zero is a multi-year experimental program designed to measure, through the weak force, the strange quark contribution to proton structure. G-Zero was financed by the U.S. Department of Energy and the National Science Foundation. In addition, significant contributions of hardware and scientific/engineering manpower were also made by CNRS in France and NSERC in Canada. To date, more than 100 scientists, 22 graduate students and 19 undergraduate students have been involved with G-Zero.

http://www.cmu.edu

About: Carnegie Mellon Universtity
The Carnegie Institution of Washington (www.carnegieinstitution.org) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Since its founding in 1900 by industrialist and philanthropist Andrew Carnegie, Carnegie Mellon University has been a pragmatic institution, adapting rapidly to change. In fewer than 100 years it has changed its name three times--each transition marking a milestone in the institution's 20th century evolution.

Whether it was Carnegie Technical Schools, as it was in its first 12 years, Carnegie Institute of Technology, its name from 1912 to 1967, or Carnegie Mellon University, three primary purposes formed its foundation. Throughout this century, Carnegie Mellon has focused on delivering distinctive and first-quality education, fostering research, creativity and discovery, and using the new knowledge created on campus to serve our larger society.

When Arthur A. Hamerschlag served as the school's first president, Carnegie Technical Schools' 12 professors and six administrators sought to educate the sons and daughters of Pittsburgh workers for employment in the region's growing industries.

These educators served the vision of Carnegie by organizing into four faculties: the School of Science and Technology, the School of Fine and Applied Arts, the School of Apprentices and Journeymen, and the Margaret Morrison Carnegie School for Women.

In its earliest years, the institution served primarily part-time and undergraduate students. The faculty, many of whom did not have doctor's degrees, focused on teaching and curriculum development.

But research efforts began as early as 1916 when the Division of Applied Psychology of the Carnegie Institute of Technology developed rating scales for job placement. This rating system was used to classify two million men for placement in the armed forces during World War I. Research bureaus were organized in coal mining, nuclear physics, applied chemistry and metallurgy.

And by granting the nation's first undergraduate degree in drama in 1917, the institution began a tradition of leadership in the arts that spanned the century.

Through research and the education of its students during the administration of President Thomas S. Baker in the 1920s and '30s, the institution began its strong tradition of transferring knowledge and skills to industry and government.

Building on this firm foundation, the administration of President Robert E. Doherty introduced a new approach to education that would be used as a model by similar institutions around the nation. The Carnegie Plan for Professional Education, initiated in 1939-40, required engineering and science students to take a quarter of their courses in a new Humanistic and Social Relations sequence. In addition, its curriculum focused on teaching students problem-solving techniques, a hallmark of the Carnegie Mellon educational experience today.

While the Doherty administration has been credited with this educational innovation, it also oversaw growth in the institution's research capability. Between 1936 and 1950, the number of graduate students grew from 36 to more than 260. The research budget ballooned from $156,000 to $1 million.

In the 1950s, the newly formed Graduate School of Industrial Administration, endowed by William Larimer Mellon, emerged as one of the three or four best business schools in the nation. (In 2004 the school was renamed the David A. Tepper School of Business after benefactor and alumnus David Tepper (MBA '82).) Today, the school is recognized as a pioneer in the field of management science and one of the top business schools in the world.

The Warner administration oversaw the institution's burgeoning research enterprise. This period of research growth was aided by the work of the institution's Computation Center, founded in 1956 to provide computing services to the campus. A major grant from benefactor Richard K. Mellon in 1965 aided the establishment of a Computer Science Department, a department which would be the genesis of Carnegie Mellon's worldwide reputation in computer science.

By the end of the Warner administration and the start of the administration of President H. Guyford Stever in 1966, Carnegie Tech had most elements of a university. Its merger in 1967 with the Mellon Institute created Carnegie Mellon University and brought a $60 million endowment, extensive research facilities and renowned research personnel to the institution.

Five years later, President Richard M. Cyert (1972-90) began a tenure that was characterized by unparalleled growth and development. The university's research budget soared from about $12 million annually in the early 1970s to more than $110 million in the late 1980s. The work of researchers in new fields such as robotics and software engineering helped the university build on its reputation for innovative ideas and pragmatic solutions to the problems of industry and society. Carnegie Mellon began to be recognized as a truly national research university able to attract students from across the nation and around the world.

The Cyert administration stressed strategic planning and comparative advantage, pursuing opportunities in areas in which Carnegie Mellon could outdistance its competitors.

An archetypal example of this approach was the introduction of the university's "Andrew" computing network in the mid-1980s. This pioneering network, which linked all computers and workstations on campus, set the standard for educational computing and firmly established the university as a leader in the uses of technology in education and research.

Education and teaching also benefited in this period with the establishment of a University Teaching Center to improve faculty teaching and the renovation of many of the university's classrooms.

Cognizant of the university's heritage, President Robert Mehrabian (1990-97) invited alumni from the era of the institution's first president, Arthur A. Hamerschlag, to attend his inauguration in 1990. President Mehrabian emphasized Carnegie Mellon's traditional strengths in education, research and service to society while focusing on initiatives for leadership in the 21st century.

With the appointment of the university's first Vice Provost for Education, President Mehrabian placed renewed emphasis early in his administration on the quality of undergraduate education. He also moved aggressively to complete the most ambitious campus building plan since the Warner era. The University Center, which opened in August 1996, and the Purnell Center for the Arts, to be completed by the fall of 1999, are keys to enhancing the quality of life on campus, another priority of the Mehrabian administration.

Confronted by shrinking governmental support of university research, President Mehrabian diversified the university's research agenda. He stressed the need to build strong relationships with the business world, matching industry's needs with the university's areas of research strength. He also put new emphasis on productivity, improvement of administrative services and strategic management of university resources.

President Mehrabian established strong, new partnerships with the greater Pittsburgh community. He led a community-wide economic development initiative, spurred collaboration with primary and secondary schools, and worked closely with local community groups.

On April 15, 1997, Jared L. Cohon, former dean of Yale University's School of Forestry and Environmental Studies, was elected by the university's Board of Trustees to succeed President Mehrabian, who resigned to spend more time with his family in California.

"Since I was chosen, since this wonderful event has occurred, it has made me reflect on why you are choosing me," President Cohon said in his first speech to the university community. "And I've said to people since this was announced that the more I think about it, the more I realize how well I think this institution and I fit together. We'll see if that's true. I think it is.

"When I was at Johns Hopkins we used to always hold up Carnegie Mellon as an example," Cohon said. "So, for many years I've ... been jealous of what has been accomplished here across departmental lines. I celebrate that. I think it is so valuable in every aspect of this university and it will position Carnegie Mellon to be even better...."

During Cohon's presidency, Carnegie Mellon has continued its trajectory of innovation and growth. Today, President Cohon is leading implementation of a comprehensive strategic plan that aims to leverage the university's existing strengths to benefit society in the areas of biotechnology and the life sciences, information and security technology, environmental science and practices, the fine arts and humanities.

The university is also committed to broadening and enhancing undergraduate education to allow students to explore various disciplines while maintaining a core focus in their primary area of study. Realizing that today's graduates must understand international issues, Carnegie Mellon is committed to providing a global education for its students and is striving to expand its international offerings and to increase its presence on a global scale. Increasing diversity, in all aspects, and fostering the economic development of southwestern Pennsylvania, are also top priorities.

Over the years Carnegie Mellon's leaders have reflected Andrew Carnegie's original dedication and commitment to this institution. In his 1900 letter to the mayor of Pittsburgh establishing Carnegie Technical Schools, Andrew Carnegie wrote, "My heart is in the work." These words have been echoed by students, faculty and administrators throughout this century and they live on the Carnegie Mellon campus today.


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