The Year of the Higgs?

The search will take place at theLarge Hadron Collider(LHC) at CERN, the world's largest particle accelerator at the European Organization for Nuclear Research in Geneva, Switzerland.

The Higgs boson is the only remainingStandard Modelparticle that has not been observed in particle physics experiments. But using two separate and complimentary experiments, the A Toroidal LHC Apparatus (ATLAS) and Compact Muon Solenoid (CMS), scientists hope to prove its existence.

Both ATLAS and CMS are particle physics detectors. They are located on opposite sides of the 27-kilometer (17-mile) LHC ring circling the countryside on the outskirts of Geneva, buried deep below ground.

The LHC has been offline during a winter break, which temporarily halted the experiments.

"The research program over this past year was essentially to commission the accelerator and the experiments to make sure that they work and they are giving us sensible results,"said physicist Aaron Dominguez of the University of Nebraska and the US CMS experiment, whose work is supported by the National Science Foundation.

The University of Nebraska researchers played an important role in building the LHC detectors and analyzing data that comes from the experiments.

Confident that everything is functioning properly, the LHC research community recently announced a decision to delay a planned shutdown of theparticle acceleratoruntil the end of 2012. If the machine continues to function at the current level, researchers believe they can explore the entire"allowed region"--the ranges of mass in which the standard model Higgs boson could exist--by the end of 2012.

"This was one of the reasons to run in 2012 and not just this year,"said Gustaaf Brooijmans of Columbia University and the US ATLAS experiment."Our projections now say that with the 2012 run we should be able to probe about 90-95 percent of the 'allowed region' for the existence of the Higgs boson."

Brooijmans' team at Columbia develops and operates the electronics that read out part of the detector.

"If theacceleratoris performing according to plan, we should have a very good first picture of this whole 'allowed range' of the standard modelHiggs boson,"said Dominguez.

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Physicists build bigger 'bottles' of antimatter to unlock nature's secrets

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While physicists routinely produce antimatter with radioisotopes and particle colliders, cooling these antiparticles and containing them for any length of time is another story. Once antimatter comes into contact with ordinary matter it"annihilates"—or disappears in a flash of gamma radiation.

Clifford Surko, a professor of physics at UC San Diego who is constructing what he hopes will be the world's largest antimatter container, said physicists have recently developed new methods to make special states of antimatter in which they can create large clouds of antiparticles, compress them and make specially tailored beams for a variety of uses.

He described the progress made in this area, including his own efforts, at the annual meeting in Washington, DC, of the American Association for the Advancement of Science. His talk,"Taming Dirac's Particle,"led off the session entitled"Through the Looking Glass: Recent Adventures in Antimatter,"on February 18.

Surko said that since"positrons"—the anti-electrons predicted by English physicist Paul Dirac some 80 years ago—disappear in a burst of gamma rays whenever they come in contact with ordinary matter, accumulating and storing these antimatter particles is no small feat. But over the past few years, he added, researchers have developed new techniques to store billions of positrons for hours or more and cool them to low temperatures in order to slow their movements so they can be studied.

Surko said physicists are now able to slow positrons from radioactive sources to low energy and accumulate and store them for days in specially designed"bottles"that have magnetic and electric fields as walls rather than matter. They have also developed methods to cool them to temperatures as low as that of liquid helium and to compress them to high densities.

"One can then carefully push them out of the bottle in a thin stream, a beam, much like squeezing a tube of toothpaste,"said Surko, adding that there are a variety of uses for such positrons.

A familiar positron technique that does not use this new technology is the PET scan, also known as Positron Emission Tomography, which is now used routinely to study human metabolic processes and help design new drugs.

In the new methods being developed by physicists, beams of positrons will be used in other ways."These beams provide new ways to study how antiparticles interact or react with ordinary matter,"said Surko."They are very useful, for example, in understanding the properties of material surfaces."

Surko and his collaborators at UC San Diego are studying how positrons bind to ordinary matter, such as atoms and molecules."While these complexes only last a billionth of a second or so,"he said,"the 'stickiness' of the positron is an important facet of the chemistry of matter and antimatter."

Surko and his colleagues are building the world's largest trap for low-energy positrons in his laboratory at UC San Diego, capable of storing more than a trillion antimatter particles at one time.

"We are now working to accumulate trillions of positrons or more in a novel 'multi-cell' trap—an array of magnetic bottles akin to a hotel with many rooms, with each room containing tens of billions of antiparticles,"he said.

"These developments are enabling many new studies of nature. Examples include the formation and study of antihydrogen, the antimatter counterpart of hydrogen; the investigation of electron-positron plasmas, similar to those believed to be present at the magnetic poles of neutron stars, using a device now being developed at Columbia University; and the creation of much larger bursts of positrons which could eventually enable the creation of an annihilation gamma ray laser."

"An exciting long-term goal of the work is the creation of portable traps forantimatter,"added Surko."This would increase greatly the ability to use and exploit antiparticles in our matter world in situations where radioisotope- or accelerator-based positron sources are inconvenient to arrange."

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A new high-resolution method for imaging below the skin using a liquid lens

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Rolland will be presenting her findings at the 2011 annual meeting of the American Association for the Advancement of Science in Washington, D.C., on Feb. 19.

"My hope is that, in the future, this technology could remove significant inconvenience and expense from the process of skin lesion diagnosis,"Rolland says."When a patient walks into a clinic with a suspicious mole, for instance, they wouldn't have to have it necessarily surgically cut out of their skin or be forced to have a costly and time-consuming MRI done. Instead, a relatively small, portable device could take an image that will assist in the classification of the lesion right in the doctor's office."

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This prototype device developed by University of Rochester Professor of Optical Engineering Jannick Rolland can take high-resolution images under the skin's surface without removing the skin. Researchers say that in the future it may eliminate the need for many biopsies to detect skin cancer. Credit: J. Adam Fenster

The device accomplishes this using a unique liquid lens setup developed by Rolland and her team for a process known asOptical CoherenceMicroscopy. In a liquid lens, a droplet of water takes the place of the glass in a standard lens. As theelectrical fieldaround the water droplet changes, the droplet changes its shape and therefore changes the focus of the lens. This allows the device to take thousands of pictures focused at different depths below the skin's surface. Combining these images creates a fully in-focus image of all of the tissue up to 1 millimeter deep in human skin, which includes importantskin tissuestructures. Because the device uses nearinfrared lightinstead of ultrasounds, the images have a precise, micron-scale resolution instead of a millimeter-scale resolution.

The process has been successfully tested in in-vivo human skin and several papers on it have been published in peer-reviewed journals. Rolland says that the next step is to start using it in a clinical research environment so its ability to discriminate between different types of lesions may be assessed.

Rolland joined the faculty of the Hajim School of Engineering and Applied Science's Institute of Optics in 2009. She is the Brian J. Thompson Professor of Optical Engineering and is also a professor of biomedical engineering and associate director of the R.E. Hopkins Center for Optical Design and Engineering.

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The physics of a sustainable society revolution

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Innovative physics will lead the way

“I decided to become a scientist when I was a second-grade student at elementary school. Reading biographies of Nobel laureates, I admired scientists for contributing to society through their work. When I was young, the most famous scientists in Japan were the physicists Hideki Yukawa and Shinichiro Tomonaga, who inspired me to become a physicist,” says Tokura.“Physicshas led to major revolutions in human society,” he points out.“A good example is electromagnetic induction discovered by the British physicist Michael Faraday in the nineteenth century.”

Electromagnetic induction is the phenomenon by which an electric current flows through a coil when a magnet is inserted into the coil and pulled out again. Its discovery led to the development of power generators, thus laying the foundation for our electricity-powered modern society. Modern civilization is critically reliant on ubiquitous supply of electrical power, all of which has been built on the discovery of electromagnetic induction.“The recent spread of information technology devices, including mobile phones, personal computers and the Internet, has dramatically changed society and economies, and even our lifestyles. This major revolution began with the emergence of semiconductor electronics, with the development of the transistor about 60 years ago. Such breakthroughs are based on physics.”

Tokura has a vision for another revolution, which he calls‘Innovation 4’. He believes that four key technological breakthroughs could once again change society as we know it: an increase in solar cell conversion efficiency to 40% or more, an increase in the thermoelectric conversion figure of merit to 4 or more, an increase in the critical temperature of superconductivity to 400 K or well above room temperature, and an in increase in battery energy density to 400 watt-hours per kilogram or more.“These numerical targets represent a tripling of existing performance indexes. Another goal is to achieve electronic information processing with minimal power consumption to conserve energy. If realized,‘Innovation 4’ will lead to a sustainable society revolution, but it is difficult to achieve these breakthroughs merely by improving existing technologies. We need to develop electronic technologies based on new principles.”

Tokura and his colleagues have been researching electronic technologies based on principles that are totally different from the mainstream semiconductor electronics of today.“It is assumed that electrons are sparse in conventional semiconductor devices, so the entanglement of electrons is weak. A group of many densely packed electrons, however, interact strongly with each other in what is known as‘a strongly correlated electron system’. In such a system, non-charge properties that are not important in semiconductors, such as electron spin and orbital, also play important roles. We are seeking to create new functions that are not possible using independent electrons alone by utilizing the features of strongly correlated electron systems. High-temperature superconductivity is another phenomenon that occurs in strongly correlated electron systems. Electronic engineering still has infinite potential.

“The electron state in strongly correlated electron systems can be described as a solid produced by electrons. The electron state is like a dilute gas in semiconductors or a liquid in metals. Just as a liquid flows when the container is inclined, electricity flows when a voltage is applied to a metal. In a strongly correlated electron system, where the electron state is‘solid’, electrons are unable to move because of mutual electrical repellence due to their dense packing. Even when a voltage is applied, no electricity flows. Hence, a strongly correlated electron system is an insulator, or specifically, a Mott insulator. When a minor stimulus such as heat, light or an electric field is applied from outside, a phase change from solid to liquid occurs instantaneously, allowing the electrons to move. In strongly correlated electron systems, this state can be changed at ultra-high speed on a nanometer scale.”

A bridge across electron functions

“In a strongly correlated electron system, cross-correlation is possible,” continues Tokura.“When a voltage is applied, an electric current flows. When a magnetic field is applied, the system becomes magnetized. These are the usual responses. By bridging different functions of the electron, unusual responses are induced. We call this phenomenon‘cross-correlation’.”

A typical example of cross-correlation (Fig. 1) is the‘colossal’ magnetoresistance effect, which was achieved with manganese oxide by Tokura in the 1990s. In this phenomenon, electric resistance decreases dramatically by a factor of one-thousand when a magnetic field is applied. This unusual response—a change in electrical resistance when a magnetic field is applied—is an example of cross-correlation. By utilizing a strongly correlated electron system, it is possible to produce a state in which an insulator lacking magnetization and a metal having magnetization compete with each other (Fig. 2). Cross-correlation allows two different functions of the electron to compete in a pair-like manner. When a magnetic field is applied to an insulator, it becomes magnetized and metallic, resulting in a dramatic drop in electric resistance.

Low-energy information processing

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Figure 2: The principle of‘colossal’ magnetoresistance. A state is created in which an insulator lacking magnetization and a metal with magnetization compete in a pair-like manner. When a magnetic field is applied to the insulator, it becomes magnetized and turns metallic, resulting in a dramatic decrease in electrical resistance. This rapid phase change can also be achieved by exposure to light or application of an electric field.

In 2007, Tokura established his own research group, the Cross-Correlated Materials Research Group, at RIKEN, and has since been conducting research on Innovation 4.“We aim to develop electronic technologies based on new principles for processing and recording information without conducting electrons.”

Existing semiconductor devices process information by conducting electrons. However, this involves the use of electrical power, and energy is wasted in the form of waste heat generated due to electric resistance. The same applies to information recording. In hard disks, for example, an electric current is passed through a coil to generate a magnetic field to reverse the orientation of magnetization in a storage bit during information recording. This also requires a electrical power, generating waste heat and wasting energy, and in large computers, the waste heat generated must be cooled using air-conditioners, consuming additional electrical power.

“If cross correlation, that is, the unusual inversion of magnetization using an electric field, rather than the inversion of magnetization using a magnetic field, could be achieved, it will be possible to record information without wasting energy and with minimal power consumption. We are working on using multiferroics to achieve this.”

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Figure 3: Ferroelectrics and ferromagnetics. Ferroelectrics and ferromagnetics permit the orientations of electrical polarization and magnetization to be reversed by applying an electric field and magnetic field, respectively.

Multiferroics exhibit both ferroelectricity and ferromagnetism. A ferroelectric (Fig. 3) exhibits polarization, with one end positively charged and the other end negatively charged, even in the absence of an external electric field. When an electric field is applied to a ferroelectric, the two poles (+ and–) reverse themselves, allowing information to be rewritten. This phenomenon is used in some prepaid‘e-money’ card systems for transport and shopping. A ferromagnetic, on the other hand, exhibits magnetization in the absence of a magnetic field, and the orientation of magnetization can be reversed by applying a magnetic field. Ferromagnetics are utilized in hard disks and other data recording devices.“In multiferroics, it is possible to realize the unusual response of reversing magnetization and simultaneously reversing the electrical polarization using an electric field by linking the orientations of electrical polarization and magnetization.”

Polarization is caused by a bias in the distribution of electrons in a material, whereas magnetization occurs when electron spins line up, which otherwise can have either upward or downward orientations, become aligned in a given orientation. Electron spin thus serves as the origin of magnetization.

“The orientation of polarization can be reversed by deforming the orbital in which the electron is accommodated. By utilizing a strongly correlated electron system of multiferroics, the orientation of electron spins can be reversed by deforming the orbital or electron cloud, which would make it possible to link the polarization and magnetization.”

In 2009, Tokura and his colleagues succeeded in experimentally changing the orientation of magnetization at temperatures below–271°C using an electric field.“If we can improve on this and simultaneously reverse the orientations of magnetization and polarization at room temperature using an electric field, then we will be able to create large-capacity memory that consumes almost no electrical power.”

More recently in June 2010, Tokura’s research group became the first in the world to directly observe skyrmion crystallization, the phenomenon by which electron spin vortices are regularly arranged like a crystal. The result attracted worldwide attention.“It is thought that these electron spin vortices can be moved with a small amount of electric current. Hence, by merely changing the orientation of electron spins one after another, it is possible to move the electron spin vertexes to achieve information processing. This has potential for information processing with minimal power consumption.”

New principles for highly efficient solar cells

“We also have an idea for dramatically improving the power efficiency of solar cells,” says Tokura. In conventional solar cells, a medium such as a semiconductor absorbs photons and generates a free pair of negative and positive charges. By separating the negative electron and positive‘hole’ and transporting them to opposite electrodes, a voltage can be produced. The light-to-electricity conversion efficiencies of modern solar cells is just over 10%, but it should be possible to improve on this efficiency.“Solar radiation contains a broad range of wavelengths. Semiconductor solar cells actually achieve nearly 100% conversion efficiency at particular wavelengths of light, because electron–hole pair can be produced from a single photon at a particular wavelength in each semiconductor with nearly 100% probability. However, an electron–hole pair is also produced when a photon with a shorter wavelength and higher energy level is absorbed, in which case the excess energy is wasted as heat. This accounts for the low power efficiency. If we use a strongly correlated electron system, the wasted energy could be used to create a metallic state and produce a large number of electrons and holes by another mechanism, which could dramatically improve conversion efficiency. Strongly correlated electron systems are being actively studied worldwide, but Tokura and his colleagues are the only group researching their use in highly efficient solar cells.

Basic science will build a bright future

“Physics will continue to yield major revolutions in human society. In recent years, however, it has become increasingly difficult for a single scientist to make a breakthrough alone.”

The Japanese government this year established the Quantum Science on Strong Correlation project with the support of the Funding Program for World-Leading Innovative R&D on Science and Technology. RIKEN is responsible for providing research support, and Tokura serves as key investigator. For this project, he has established a dedicated research group, the Correlated Electron Research Group.“This project aims to set groundbreaking principles for realizing Innovation 4 through integrated joint research among outstanding researchers in a broad range of fields, including physics theory, thin-film growth, structural analysis and instrumentation measurement technology. However, if someone ordered me to produce results that could be used in practical applications within several years, I would struggle. Faraday, when asked about why his discovery ofelectromagnetic inductionwas so important, answered,”Who can predict what a newborn baby will become?” The usefulness of the results of basic research like ours is sometimes unpredictable. In the long term, 50 or 100 years, however, they have the potential to produce major revolutions and contribute greatly to future society.”

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Ice offers possible explanation for Death Valley's mysterious 'self-moving' rocks

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In the remote, almost totally dry lakebed called Racetrack Playa, some of the rocks move themselves across the desert floor when people aren't watching.

Scientists know the rocks move because they leave narrow tracks trailing behind them, but they haven't actually seen it happen. And although one can't entirely rule out the possibility of some prank being played, at least some of the rocks appear to be moving under natural circumstances.

It doesn't rain often in Racetrack Playa, and when it does the lakebed can flood. The rocks don't float exactly, but the main explanation for their movement is that moisture can make the mud on which the rocks sit more slick, making it easier for high winds to push the rocks along. Another explanation offered is that the temporary deposit of water, chilled to form extensive sheets of ice, might help to reflect and focus the winds, making it easier for the rocks to move.

The winds required to move rocks in this way would seem to be at the level of 100 mph or more. That's why the rocks are sometimes referred to as"sailing stones."They are rare but they have been noticed in Racetrack Playa and a few other arid places around the world subject to occasional floods

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The track left from a"self-moving"rock. Credit: Courtesy of Ralph Lorenz

Ralph Lorenz, a scientist at Johns Hopkins University, offers a new explanation. The rocks are actually lifted up by the ice, or at least made more buoyant by the ice, making it easier for the rocks to migrate. If the rocks are moving about on ice rafts, the ground below cannot offer as muchresistanceagainst their motion and the winds needed for movement wouldn't have to be as great, he argued.

So why hasn't the motion been observed?

"Movement happens for only tens of seconds, at intervals spaced typically by several years,"said Lorenz."This would demand exceptional patience as well as luck."

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So, the rocks are probably traveling on the coldest and windiest days that occur over a period of several years. The most likely time would be in the very early dawn. Little wonder no one is around to witness the event.

Lorenz and his colleagues would like to install inexpensive time-lapse monitoring of the Playa area, using digital cameras. The lakebed is about 2.5 miles long and 1.25 miles wide. They have also performed some laboratory tests by blowing on ice-assisted rocks. These simple tests support the ice-raft hypothesis. The results appear in the January 2011 issue of theAmerican Journal of Physics.

An additional reason for studying the rocks of Racetrack Playa is that its qualities resemble those at a drying-up lake on Saturn's moon Titan. Pictures taken by the Cassini-Huygens mission reveal what look like river channels, cobblestones, and lake beds or mud flats. Only at Titan's"Ontario Lacus,"as one interesting site is called, the runoff consists of liquid hydrocarbons, not water. Some pictures even seem to be showing a"bathtub ring"left by what is probably a drying lake.

One of Lorenz's colleagues, Brian K. Jackson, who works at NASA's Goddard Space Flight Center, also likes the idea that their research at Racetrack Playa has a dual purpose.

"It's been exciting trying to solve a mystery that has resisted solution for sixty years,"Jackson said."Scientific accounts of the Racetrack Playa rocks go back to at least 1948, and there were certainly stories about the playa long before that."

And Jackson also believes discoveries in Death Valley, here on Earth, will help us to better understand similar real estate on Titan or Mars.

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The Daya Bay Reactor Neutrino Experiment: On track to completion

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What the researchers find at Daya Bay will bear on some of the most intriguing questions in basicphysics: how much do different kinds ofneutrinosweigh? And which kind is the heaviest? By weighing neutrinos scientists hope to learn how electrons and their cousins, muons and tau particles, came into existence in the moments after the big bang. The answers could explain why there is more matter than antimatter in the universe– and indeed why there is any matter at all.

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The heart of the Near Hall is a pool of ultrapure water in which the antineutrino detectors will be submerged, shielded from radioactive decays in the surrounding rock by more than two meters of water on all sides. The pool is lined with PMTs to track any“stiff” (highly energetic) cosmic rays that make it all the way through the overlying rock. The blue supports beyond the pool indicate where a different kind of detector is being constructed, which will roll over the water pool like a roof and help locate the position of any cosmic rays that enterthe water.

Clues to neutrino mass lie in measuring how one“flavor” of neutrino changes into another. (Electron neutrinos, muon neutrinos, and tau neutrinos, the three flavors, are named after the leptons with which each is associated.) The crucial value, writtenθ₁₃, is a term known as“neutrino mixing angle theta one three”– and the Daya Bay experiment is intended to measure it to within a few degrees. The following tour of the experimental site shows how the researchers hope to do it.

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Unique new probe of proton spin structure at Relativistic Heavy Ion Collider

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“Exploring the mystery of protonspinhas been one of the key scientific research goals at RHIC,” said Steven Vigdor, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics.“Like many scientific mysteries, this one turns out to be more complex the more we learn about it. The W boson measurements were enabled by new detection techniques at RHIC’s STAR and PHENIX experiments and by extending RHIC’s world-record energies for the acceleration of proton beams with a distinct spin orientation preference. The results will allow us to tease apart subtle details that were previously inaccessible, and should move the field closer to a quantitative understanding of proton spin structure and dynamics.”

Spin is a quantum property that describes a particle’s intrinsic angular momentum. Like charge and mass, it’s part of a particle’s identity, whose magnitude is the same for all particles of a given type. But unlike charge and mass, spin has a direction that can be oriented differently for individual particles of a given species. The interactions among particles inside atoms, nuclei, and protons depend critically on their relative spin orientations, with influence on a wide range of electrical, magnetic, optical, and other properties of matter. Yet despite the fact that proton spin is used in everyday applications like magnetic resonance imaging (MRI), exactly how— and how much— the individual particles that make up protons contribute to spin remains a mystery.

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PHENIX Detector

Scientists know that the quarks inside a proton each have their own intrinsic spin. But numerous experiments have confirmed that a directional preference among all these quark spins can account for only about 25 percent of the proton’s total spin. RHIC was built with the ability to collide polarized protons— protons whose spins could be aligned in a controlled way— so scientists could probe other factors that might account for the“missing” spin. Much of the equipment needed to realize this unique capability was provided by the RIKEN Institute of Physical and Chemical Research of Japan, whose researchers form a critical part of the international collaborations carrying out this work.

After beginning polarized proton collisions at RHIC late in 2001, the first place the scientists looked for the missing spin was the gluons, the particles that hold a proton’s quarks together via the strong force.

“The shock so far has been that we haven’t found gluons carrying much of the spin,” said PHENIX spokesperson Barbara Jacak, a physicist at Stony Brook University. Measurements from the STAR detector agree. After several polarized proton runs at various energies, RHIC data suggest with more and more certainty that gluons contribute much less than originally speculated to proton spin, so the source of the spin still remains a mystery.

The scientists acknowledge that they haven’t been able to look at all the gluons, particularly those that carry tiny fractions of the proton’s overall momentum.“It’s like we’re looking for missing keys under a narrow-focus street lamp, and we’d like a lamp with broader illumination,” Jacak said.

But as they continue to work on that part of the puzzle, they also have a new way to look at spin.

Thanks to new detection techniques and the ability to run polarized proton collisions at very high energies— 500 GeV, or 500 billion electron volts— RHIC scientists at both PHENIX and STAR are able to directly probe the polarization contributions from different flavored quarks (known by the names“up” and“down”) inside protons for the first time.

“All of the earlier measurements that attempted to separate quark spin contributions according to flavor were done indirectly, and they looked primarily at the contribution of the three leading, or valence, quarks in the proton,” said Bernd Surrow, a Massachusetts Institute of Technology physicist and deputy spokesperson of the STAR collaboration.“This new method of measuring W bosons gives us direct access to quarks known as‘sea quarks,’ which wink in and out of existence as gluons split and reform within the protons.”

Sea quarks are always produced in quark/antiquark pairs and have exceedingly short lifetimes. But at the very high energies achieved in RHIC’s colliding proton beams, these fleeting quarks and antiquarks can collide, or interact, to produce relatively heavy W bosons. So far, RHIC’s experiments have detected Ws by looking for electrons and positrons (positively charged electrons) that form as the Ws decay. The charge of the decay products— whether electrons or positrons— directly reflects the charge of the Ws, which in turn tells what flavor of antiquarks were involved in the collision— whether anti-up or anti-down.

By comparing the number of Ws produced when bunches of RHIC’s colliding protons are polarized in the direction of the beam’s motion with the number produced when the protons are polarized in the opposite direction, the scientists can directly measure the degree to which the antiquark spins point in a preferred direction with respect to the overall proton spin. This robust measurement technique relies on a fundamental, and very well understood, property of the weak interaction by which the Ws are produced, namely, its extreme violation of mirror symmetry.

“Observation of this extreme effect in weak interactions for the first time in polarized proton-proton collisions at RHIC is itself a major milestone,” said Hideto En’yo, director of the RIKEN Nishina Center for Accelerator-Based Science, which established the RIKEN-BNL Research Center (RBRC) to nurture a new generation of physicists interested in studying the strong force and spin physics at RHIC.“It is gratifying to see our large investments in polarization equipment pay off with such large and cleanly interpretable spin effects.”

“You would think you would get equal numbers of anti-up and anti-down quarks inside a proton. But previous experiments have shown that they are very different,” Surrow said.“That means there is a lot of uncertainty about the underlying mechanism of how these sea quarks pop in and out of existence. It also indicates that the different flavors may behave differently in terms of how they contribute to spin.”

Added Jacak,“Understanding these differences won’t by itself solve the spin mystery, but it will give us a clearer picture of one piece of the puzzle, the sea quark contribution.”

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