Below the Fold

JLab Experiment Probes Short-Range Correlations

Eli Piasetzky, a professor at Tel Aviv University, is a spokesperson for the experiment.

But where the nucleus of the atom is concerned, the quirky laws of physics are a little different. There, an attraction between the positively charged proton and the neutral neutron holds the nucleus together.

Sometimes, a proton and a neutron may get even closer, forming a brief pairing, a phenomenon known as a short-range correlation. A proton can also pair with another proton and a neutron can pair with another neutron. For simplicity, scientists refer to both protons and neutrons as nucleons.

Oddly enough, these pairs of nucleons are the main source of high-velocity nucleons in nuclei. It's thought that when the nucleons get too close, they violently repel each other, and fly off at high speeds in opposite directions.

"We've known for a very long time that there are nucleons that are moving very fast in the nucleus. It's a kind of puzzle in nuclear physics, how these fast nucleons acquire their high velocity," said Eli Piasetzky, a professor at Tel Aviv University and a spokesperson on the experiment. "One resolution was that they were going very fast because they were getting very close to each other, and we wanted to check this."

Previous experiments at JLab have shown that roughly one-fifth of all nucleons in the nucleus were in a short-range correlation. To learn more, Piasetzky and his colleagues, following a theoretical prediction by Mark Strikman and Leonid Frankfurt, set out to directly and simultaneously measure the constituents of the short-range correlations.

The experiment was conducted in Jefferson Lab's Hall A. In the experiment, a beam of energetic electrons was sent into a thin sheet of carbon. The scientists were interested in the electrons that struck protons engaged in a short-range correlation.

The deflected electrons and struck protons were measured in Hall A's High Resolution Spectrometers. The partners in each short-range correlated pair, protons or neutrons, were measured in the BigBite large acceptance spectrometer and a neutron detector.

"These correlated nucleons have a high relative momentum. If you knock one out one way, the correlated nucleon will fly out in the opposite direction," noted JLab Staff Scientist Doug Higinbotham. "We set up our detectors to take advantage of this."

The experiment found that for almost every high-momentum proton kicked out of the nucleus, there was also a nucleon detected in the opposite direction. That means that the main reason for nucleons having high momentum is the fact that they are members of a correlated pair.

Moreover, most of the protons kicked out were accompanied with neutrons going in the opposite direction. The experiment showed that there are 18 times more short-range correlation neutron/proton pairs than proton/proton pairs in a carbon nucleus. The carbon nucleus has an equal number of protons and neutrons.

"It shows, for the first time in a very clear and unambiguous way, this fact that the large momentum nucleons in nuclei are coming in pairs. And they're coming mainly in proton/neutron pairs," said Piasetzky.

Higinbotham agreed. "The result from this experiment is like finding that missing piece needed to finish a puzzle. This experiment, combined with others, gives us a very coherent picture of these short-range correlations in the nucleus."

Calculations of this effect in recent theoretical work by Misak Sargsian et al. and Rocco Schiavilla et al. indicate that it is robust and does not depend on the exact parameterization of the force between nucleons, the type of the nucleus, or the exact ground-state wave-function used to describe the nucleons.

When combined with a theoretical calculation of the effects of proton/neutron correlations on the momentum distribution of the nucleons in neutron stars, the result also indicates that the presence of short-range correlations may have a disproportionately large effect on neutron star structure.

Doug Higinbotham, JLab staff scientist, is a spokesperson for the experiment.

Now the collaboration members are looking to extend their studies of short-range correlations. "We want to push to the limit where they start repelling each other and try to understand this – to see what happens to two nucleons when they are even closer," Piasetzky said.

The experiment collaboration includes more than 60 members from 31 national and international institutions. The collaboration was led by Doug Higinbotham and Steve Wood (JLab.), Shalev Gilad (MIT), John Watson (KSU) and Eli Piasetzky (Tel Aviv U.). Three graduate students: Peter Monaghan (MIT), Ran Shneor (Tel Aviv U.), and Ramesh Subedi (KSU) analyzed the data as part of their Ph.D. theses. This work was supported by the U.S. Department of Energy; the U.S. National Science Foundation; the Israel Science Foundation; the U.S.-Israeli Bi-national Scientific Foundation; the UK Engineering and Physical Sciences Research Council and the Science & Technology Facilities Council.

By Kandice Carter
JLab science writer

Further Reading
The paper was published online by the journal Science, at the Science Express website, on May 29, 2008.
BigBite does its stuff
BigBite is Reborn
Description of SRC research at Brookhaven National Lab
JLab News Release:  Protons Pair Up With Neutrons

This story was featured recently on Jefferson Lab's main webpage: http://www.jlab.org/news/articles/2008/Nuclear_Pairs.html

Senator John Miller Visits JLab

Virginia state Sen. John C. Miller, 1st District, visited JLab June 3. Steve Suhring, operations manager, (right) explains accelerator display screens in the Machine Control Center to Miller (center) and Lab Director Christoph Leemann.

Virginia state Sen. John C. Miller visited Jefferson Lab June 3 and toured the facility.

Miller, representing Virginia's 1st District, visited Jefferson Lab to gain a better understanding of the lab's research program and its economic impact on Virginia.

He took the opportunity to tour the accelerator control room (Machine Control Center) one of the Lab's cavernous end stations (Hall A) where physics experiments are run. He also visited the Free-Electron Laser and Dilon Technologies, a medical imaging company that licenses JLab-developed detector technology and is based in the Applied Research Center.

Miller learned about JLab's advances in its scientific mission, the study of the building blocks of the nucleus of the atom. He also received information about the planned upgrade of the JLab's research capabilities and its impact on the future of U.S. science. Additionally, he heard about the lab's applied-science experiments at the Free-Electron Laser facility.

Miller was impressed with the depth and breadth of JLab's basic science and technology transfer programs and with the unique nature of the facilities that JLab provides to the research community.

JLab Expertise Helps NASA With Deep-Space Research

Members of JLab's Cryogenics Department are lending their super-cool expertise to a NASA project. From left to right are Robert Norton, Jonathan Creel, Peter Knudsen, Venkatarao "Rao" Ganni, group leader Dana Arenius and Ahmed Sidi-Yekhlef Members of Jefferson Lab's Cryogenics Department are among the planet's best at what they do. Now they're lending their super-cool expertise to a project that's out of this world. They're helping NASA in testing its James Webb Space Telescope, the next generation of space-based technology that will replace the Hubble Space Telescope.       For more about the JLab Cryogenics Department's work with NASA, visit http://www.jlab.org/news/articles/2008/A_Bigger_Chill.html

Teacher Enrichment Program Earns Award

Jan Tyler (left), JLab's Science Education manager, accepts a Programs That Work award from Virginia Secretary of Education Thomas Morris. The Department of Energy's Academies Creating Teacher Scientists program at JLab was one of the five programs from across Virginia that was recognized with the award.

In mid-May, the Virginia Mathematics and Science Coalition presented its "Programs That Work" award to five teacher programs across the commonwealth. This award is given out every five years. The Department of Energy's Academies Creating Teacher Scientists (ACTS) program at Jefferson Lab was one of the five programs recognized. Virginia Secretary of Education Thomas Morris, who spoke on behalf of Gov. Tim Kaine at the awards presentation, recalled his meeting with ACTS teachers last summer during his visit to JLab.

Jan Tyler, JLab's Science Education manager, attributes much of the program's success to the "tremendous volunteer support – year after year. The scientific and engineering staff members that work with the teachers have long-lasting effects on the teachers and their students. The combined efforts of the JLab community have created an environment in which staff are allowed and encouraged to participate in the lab's science education programs."

For additional information about ACTS and other teacher and student enrichment programs conducted at Jefferson Lab and other DOE facilities, visit these links: http://education.jlab.org/indexpages/program.php
http://www.scied.science.doe.gov/scied/sci_ed.htm

JLab Work Featured at SURA Terahertz Applications Symposium

The Free-Electron Laser Division's Gwyn Williams stops at the Southeastern Universities Research Association display during the Terahertz Applications Symposium held recently in Washington, D.C.

"It is significant to note that this conference has grown strongly year by year, and is the only conference in the field that is dedicated to cross-fertilization of industry, academia and government agencies," says JLab's Gwyn Williams, of the Free-Electron Laser Division.

Copies of the presentations from all 24 speakers may be ordered online at www.sura.org/thz.

The event is sponsored by SURA. This year, for the first time, there was a small trade show with industrial sponsors from seven companies: the Institute for the Development and Commercialization of Advanced Sensor Technology (IDCAST); Mictotech Instruments; Teraview; Toptica; T-Ray Science; Virginia Diodes and Zomega.

The conference has spawned a number of collaborations both within the industry, and between industry, academia, government agencies and research laboratories, and is an important aspect of the meeting, according to Williams. Five years ago, there was no major THz technology in the industrial arena. Since then it has been used in trials in quality control applications in the aerospace, pharmaceutical and medical industries. Many such applications were reported this year, in addition to several research groups' reports on advances in basic science with THz.

A highlight of the meeting was the deployment of passive sub-millimeter imaging systems, with two companies showing dramatic images of security screening at airports and company warehouses.

Featured at the meeting was the ongoing work of the THz Research Group at JLab, presented by Mike Klopf, who run's JLab's THz lab. The Free-Electron Laser at JLab houses the world’s most powerful broadband THz source, generating tens of watts of power, a million times more powerful than the nearest competitor.

The conference was originated by Matt Thomas, then business development manager of SURA, after extensive discussions with JLab staff, including Williams, following the demonstration of high-power terahertz (THz) in the infrared demonstration Free-Electron Laser at JLab.

DOE Launches Website with Energy Saving Tips for Consumers

The Department of Energy recently launched a new Internet feature that provides tips to consumers on how to make smart energy choices to save money while protecting the environment. The interactive webpage shows consumers steps to use less energy with household electronics, lighting, and appliances to save on monthly bills and how to avoid wasting energy by improving the energy efficiency of their homes and cars.

The site also features the DOE's work to develop cleaner, more affordable, diverse, reliable and sustainable energy sources supporting the President's goal to stop the growth of U.S. greenhouse gas emissions by 2025 while meeting increasing energy demands. 

DOE and its 17 world-class national laboratories, in partnership with private industry and universities, perform cutting-edge research to meet these challenges and develop innovative energy solutions in areas such as cellulosic biofuels, solar, geothermal, nuclear, and clean coal power. Other areas of emphasis include DOE's work to make a smart and efficient electric transmission grid, make homes, buildings and industrial sites more energy efficient, and reduce dependence on oil with plug-in hybrid electric vehicles and hydrogen-powered cars. For more information, visit the DOE website.

Milestones for April 2008

Hello
Dean Carroll, Computer Center Student Intern, Information Technology Division
Gina Dixon, Environmental Monitoring Engineer, Environment, Safety, Health & Quality Division
Phillip Kessler, Project Planner, Project Management and Integration Office
Mary Logue, Associate Director, Environment, Safety Health & Quality Division
Russell Moy, Senior Advisor & General Council, Southeastern Universities Research Association
Richard Owen, Industrial Hygiene Lead; Environment, Safety, Health & Quality Division
Anthony Reilly, Superconducting Radio Frequency Chemical Engineer, Accelerator Operations, Research & Develop Division

Goodbye
Julie Leverenz, Procurement, Office of the Chief Financial Officer, Retired
Hugh Loweth, Vice President for Government and University Relations, Southeastern Universities Research Association, Retired
Richard Lusk, Contract Manager, Office of the Chief Financial Officer, Retired
Nikolitsa "Lia" Merminga, Director, Center for Advanced Studies of Accelerators, Accelerator Operations, Research & Develop Division
Matt Thomas, SURA Business Development Manager, Southeastern Universities Research Association