From DOE’s Brookhaven National Laboratory (US) : “BNL’s Zhangbu Xu and others prove 87-year-old theories of famous physicists”

From DOE’s Brookhaven National Laboratory (US)

August 21, 2021
Daniel Dunaief

Zhangbu Xu at the STAR detector.

Zhangbu Xu in front of the time-of-flight detector, which is important for identifying the electrons and positrons the STAR Collaboration measured. Photo from BNL.

Gregory Breit and John Wheeler were right in the 1930s and Werner Heisenberg and Hans Heinrich Euler in 1936 and John Toll in the 1950s were also right.

Breit, who was born in Russia and came to the United States in 1915, and Wheeler, who was the first American involved in the theoretical development of the atomic bomb, wrote a paper that offered theoretical ideas about how to produce mass from energy.

Breit and Wheeler suggested that colliding light particles could create pairs of electrons and their antimatter opposites known as positrons. This idea was an extension of one of Albert Einstein’s most famous equations, E=mc2, converting pure energy into matter in its simplest form.

Working at the Relativistic Heavy Ion Collider (RHIC)[below] at Brookhaven National Laboratory, a team of scientists in the STAR Collaboration [below] has provided experimental proof that the ideas of some of these earlier physicists were correct.

“To create the conditions which the theory predicted, even that process is quite exhausting, but actually quite exciting,” said Zhangbu Xu, a senior scientist at BNL in the physics department.

The researchers published their results recently in Physics Review Letters, which provides a connection to Breit and Wheeler, who published their original work in a predecessor periodical called Physics Review.

While Breit and Wheeler wrote that the probability of two gamma rays colliding was “hopeless,” they suggested that accelerated heavy ions could be an alternative, which is exactly what the researchers at RHIC did.

The STAR team, for Solenoidal Tracker at RHIC, also proved another theory proposed decades ago by physicists Heisenberg, who also described the Heisenberg Uncertainty Principle, and Hans Heinrich Euler in 1936 and John Toll, who would later become the second president at Stony Brook University (US), in the 1950s.

These physicists predicted that a powerful magnetic field could polarize a vacuum of empty space. This polarized vacuum should deflect the paths of photons depending on photon polarization.

Researchers had never seen this polarization-dependent deflection, called birefringence, in a vacuum on Earth until this set of experiments.

Creating mass from energy

Xu and others started with a gold ion. Without its electrons, the 79 protons in the gold ion have a positive charge, which, when projected at high speeds, triggers a magnetic field that spirals around the particle as it travels.

Once the ion reaches a high enough speed, the strength of the magnetic field equals the strength of the perpendicular electric field. This creates a photon that hovers around the ion.

The speeds necessary for this experiment is even closer to the speed of light, at 99.995%, than ivory soap is to being pure, at 99.44%.

When the ions move past each other without colliding, the photon fields interact. The researchers studied the angular distribution patterns of each electron and its partner positron.

“We also measured all the energy, mass distribution, and quantum numbers of the system,” Daniel Brandenburg, a Goldhaber Fellow at BNL who analyzed the STAR data, said in a statement.

Even in 1934, Xu said, the researchers realized the cross section for the photons to interact was so small that it was almost impossible to create conditions necessary for such an experiment.

“Only in the last 10 years, with the new angular distribution of e-plus [positrons] and e-minus [electrons] can we say, ‘Hey, this is from the photon/ photon creation,’” Xu said.

Bending light in a vacuum

Heisenberg and Euler in 1936 and Toll in the 1950’s theorized that a powerful magnetic field could polarize a vacuum, which should deflect the paths of photons. Toll calculated in theory how the light scatters off strong magnetic fields and how that connects to the creation of the electron and positron pair, Xu explained. “That is exactly what we did almost 70 years later,” he said.

This is the first experiment on Earth that demonstrates experimentally that polarization affects the interactions of light with the magnetic field in a vacuum.

Xu explained that one of the reasons this principle hasn’t been observed often is that the effect is small without a “huge magnetic field. That’s why it was predicted many decades ago, but we didn’t observe it.”

Scientists who were a part of this work appreciated the connection to theories their famous and successful predecessors had proposed decades earlier.

“Both of these findings build on predictions made by some of the great physicists in the early 20th century,” Frank Geurts, a professor at Rice University (US), said in a statement.

The work on bending light through a vacuum is a relatively new part of the research effort.

Three years ago, the scientists realized they could study this, which was a surprising moment, Xu said.

“Many of our collaborators (myself included) did not know what vacuum birefringence was a few years ago,” he said. “This is why scientific discovery is exciting. You don’t know what nature has prepared for you. Sometimes you stumble on something exciting. Sometimes, there is a null set (empty hand) in your endeavor.

Xu lives in East Setauket. His son Kevin is earning his bachelor’s degree at The University of Pennsylvania (US), where he is studying science and engineering. His daughter Isabel is a junior at Ward Melville High School.

As for the recent work, Xu, who earned his PhD and completed two years of postdoctoral research at Yale Unversity (US) before coming to BNL, said he is pleased with the results.

“I’ve been working on this project for 20 years,” he said. “I have witnessed and participated in quite a few exciting discoveries RHIC has produced. These are very high on my list.”

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One of ten national laboratories overseen and primarily funded by the DOE(US) Office of Science, DOE’s Brookhaven National Laboratory (US) conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University(US), the largest academic user of Laboratory facilities, and Battelle(US), a nonprofit, applied science and technology organization.

Research at BNL specializes in nuclear and high energy physics, energy science and technology, environmental and bioscience, nanoscience and national security. The 5,300 acre campus contains several large research facilities, including the Relativistic Heavy Ion Collider [below] and National Synchrotron Light Source II [below]. Seven Nobel prizes have been awarded for work conducted at Brookhaven lab.

BNL is staffed by approximately 2,750 scientists, engineers, technicians, and support personnel, and hosts 4,000 guest investigators every year. The laboratory has its own police station, fire department, and ZIP code (11973). In total, the lab spans a 5,265-acre (21 km^2) area that is mostly coterminous with the hamlet of Upton, New York. BNL is served by a rail spur operated as-needed by the New York and Atlantic Railway. Co-located with the laboratory is the Upton, New York, forecast office of the National Weather Service.

Major programs

Although originally conceived as a nuclear research facility, Brookhaven Lab’s mission has greatly expanded. Its foci are now:

Nuclear and high-energy physics
Physics and chemistry of materials
Environmental and climate research
Energy research
Structural biology
Accelerator physics


Brookhaven National Lab was originally owned by the Atomic Energy Commission(US) and is now owned by that agency’s successor, the United States Department of Energy (DOE). DOE subcontracts the research and operation to universities and research organizations. It is currently operated by Brookhaven Science Associates LLC, which is an equal partnership of Stony Brook University(US) and Battelle Memorial Institute(US). From 1947 to 1998, it was operated by Associated Universities, Inc. (AUI) (US), but AUI lost its contract in the wake of two incidents: a 1994 fire at the facility’s high-beam flux reactor that exposed several workers to radiation and reports in 1997 of a tritium leak into the groundwater of the Long Island Central Pine Barrens on which the facility sits.


Following World War II, the US Atomic Energy Commission was created to support government-sponsored peacetime research on atomic energy. The effort to build a nuclear reactor in the American northeast was fostered largely by physicists Isidor Isaac Rabi and Norman Foster Ramsey Jr., who during the war witnessed many of their colleagues at Columbia University leave for new remote research sites following the departure of the Manhattan Project from its campus. Their effort to house this reactor near New York City was rivalled by a similar effort at the Massachusetts Institute of Technology (US) to have a facility near Boston, Massachusettes(US). Involvement was quickly solicited from representatives of northeastern universities to the south and west of New York City such that this city would be at their geographic center. In March 1946 a nonprofit corporation was established that consisted of representatives from nine major research universities — Columbia University(US), Cornell University(US), Harvard University(US), Johns Hopkins University(US), Massachusetts Institute of Technology(US), Princeton University(US), University of Pennsylvania(US), University of Rochester(US), and Yale University(US).

Out of 17 considered sites in the Boston-Washington corridor, Camp Upton on Long Island was eventually chosen as the most suitable in consideration of space, transportation, and availability. The camp had been a training center from the US Army during both World War I and World War II. After the latter war, Camp Upton was deemed no longer necessary and became available for reuse. A plan was conceived to convert the military camp into a research facility.

On March 21, 1947, the Camp Upton site was officially transferred from the U.S. War Department to the new U.S. Atomic Energy Commission (AEC), predecessor to the U.S. Department of Energy (DOE).

Research and facilities

Reactor history

In 1947 construction began on the first nuclear reactor at Brookhaven, the Brookhaven Graphite Research Reactor. This reactor, which opened in 1950, was the first reactor to be constructed in the United States after World War II. The High Flux Beam Reactor operated from 1965 to 1999. In 1959 Brookhaven built the first US reactor specifically tailored to medical research, the Brookhaven Medical Research Reactor, which operated until 2000.

Accelerator history

In 1952 Brookhaven began using its first particle accelerator, the Cosmotron. At the time the Cosmotron was the world’s highest energy accelerator, being the first to impart more than 1 GeV of energy to a particle.

The Cosmotron was retired in 1966, after it was superseded in 1960 by the new Alternating Gradient Synchrotron (AGS).

The AGS was used in research that resulted in 3 Nobel prizes, including the discovery of the muon neutrino, the charm quark, and CP violation.

In 1970 in BNL started the ISABELLE project to develop and build two proton intersecting storage rings.

The groundbreaking for the project was in October 1978. In 1981, with the tunnel for the accelerator already excavated, problems with the superconducting magnets needed for the ISABELLE accelerator brought the project to a halt, and the project was eventually cancelled in 1983.

The National Synchrotron Light Source (US) operated from 1982 to 2014 and was involved with two Nobel Prize-winning discoveries. It has since been replaced by the National Synchrotron Light Source II (US) [below].

After ISABELLE’S cancellation, physicist at BNL proposed that the excavated tunnel and parts of the magnet assembly be used in another accelerator. In 1984 the first proposal for the accelerator now known as the Relativistic Heavy Ion Collider (RHIC)[below] was put forward. The construction got funded in 1991 and RHIC has been operational since 2000. One of the world’s only two operating heavy-ion colliders, RHIC is as of 2010 the second-highest-energy collider after the Large Hadron Collider(CH). RHIC is housed in a tunnel 2.4 miles (3.9 km) long and is visible from space.

On January 9, 2020, It was announced by Paul Dabbar, undersecretary of the US Department of Energy Office of Science, that the BNL eRHIC design has been selected over the conceptual design put forward by DOE’s Thomas Jefferson National Accelerator Facility [Jlab] (US) as the future Electron–ion collider (EIC) in the United States.

In addition to the site selection, it was announced that the BNL EIC had acquired CD-0 (mission need) from the Department of Energy. BNL’s eRHIC design proposes upgrading the existing Relativistic Heavy Ion Collider, which collides beams light to heavy ions including polarized protons, with a polarized electron facility, to be housed in the same tunnel.

Other discoveries

In 1958, Brookhaven scientists created one of the world’s first video games, Tennis for Two. In 1968 Brookhaven scientists patented Maglev, a transportation technology that utilizes magnetic levitation.

Major facilities

Relativistic Heavy Ion Collider (RHIC), which was designed to research quark–gluon plasma and the sources of proton spin. Until 2009 it was the world’s most powerful heavy ion collider. It is the only collider of spin-polarized protons.
Center for Functional Nanomaterials (CFN), used for the study of nanoscale materials.
BNL National Synchrotron Light Source II(US), Brookhaven’s newest user facility, opened in 2015 to replace the National Synchrotron Light Source (NSLS), which had operated for 30 years.[19] NSLS was involved in the work that won the 2003 and 2009 Nobel Prize in Chemistry.
Alternating Gradient Synchrotron, a particle accelerator that was used in three of the lab’s Nobel prizes.
Accelerator Test Facility, generates, accelerates and monitors particle beams.
Tandem Van de Graaff, once the world’s largest electrostatic accelerator.
Computational Science resources, including access to a massively parallel Blue Gene series supercomputer that is among the fastest in the world for scientific research, run jointly by Brookhaven National Laboratory and Stony Brook University.
Interdisciplinary Science Building, with unique laboratories for studying high-temperature superconductors and other materials important for addressing energy challenges.
NASA Space Radiation Laboratory, where scientists use beams of ions to simulate cosmic rays and assess the risks of space radiation to human space travelers and equipment.

Off-site contributions

It is a contributing partner to ATLAS experiment, one of the four detectors located at the Large Hadron Collider (LHC).

It is currently operating at CERN near Geneva, Switzerland.

Brookhaven was also responsible for the design of the SNS accumulator ring in partnership with Spallation Neutron Source at DOE’s Oak Ridge National Laboratory (US), Tennessee.

Brookhaven plays a role in a range of neutrino research projects around the world, including the Daya Bay Neutrino Experiment (CN) nuclear power plant, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China.

Brookhaven Campus.