Category Archives: Physics

A quark like no otherw

A University of Iowa physicist is at the forefront of the search for a missing particle that could prove whether the Higgs boson—believed to give mass to all matter—exists.

Usha Mallik and her team helped build a sub-detector at the Large Hadron Collider, the world’s largest and most powerful particle accelerator, located in Switzerland. They’re running experiments on the sub-detector to search for a pair of bottom quarks—subatomic yin-and-yang particles that should be produced about 60 percent of the time a Higgs boson decays.

Evidence of these bottom quarks would confirm the existence of the Higgs boson, sometimes referred to as the “God particle.” The Higgs’ apparent discovery in 2012 seemed to support the Standard Model, the prevailing theory in physics about how the laws governing the universe work.

But since that find, there’s been a hitch: The bottom quarks expected to arise from a Higgs boson’s decay have yet to be seen, and scientists need that to happen to know for sure the Higgs, in fact, exists.

“Until we’re sure whether it’s a Standard Model Higgs or an imposter mixed with another kind of Higgs, we are desperate to learn what is beyond the Standard Model. The Higgs is our window beyond the Standard Model,” Mallik says.

Still, the quest remains complicated: A Higgs boson is created about once in 10 trillion tries. Moreover, Higgs bosons decay into other particles almost instantly after they are produced, which makes detecting and defining their decaying constituents—such as the bottom quarks—even more challenging.

Mallik and her team hope to observe bottom quarks by following the post-collision clutter that arises from the decay of the Higgs or other new heavy particles similar to it.

“It’s basically identifying, picking that needle in the haystack while not getting fooled by something else,” says Mallik, who spent the past academic year at ATLAS, one of four particle detectors at the Large Hadron Collider. “That is the challenge.”

Mallik, three postdoctoral researchers, a graduate student, and a software engineer from the UI have all been at ATLAS sifting through the voluminous data produced by the collisions. Their work is funded through the U.S. Department of Energy.

Anindya Ghosh, a first-year UI graduate student from India joined Mallik’s group in 2015 after hearing her speak the year before at the Indian Institute of Technology in Madras, India. Ghosh worked with the ATLAS experiments over most of last summer.

He calls it “a fantastic place” to be, with hundreds of scientists, students, and teachers joined in the same quest.

“It’s a really great opportunity for a new student like me to learn from the experts,” Ghosh says.

The attempt to understand the underpinnings of the universe—and human existence—has always fascinated Mallik.

“It’s always interested me,” she says. “How did we come into being? What led to our universe? It’s a fundamental question in many forms.”

Source: University of Iowa


NIST Physicists ‘Squeeze’ Light to Cool Microscopic Drum Below Quantum Limit

Physicists at the National Institute of Standards and Technology (NIST) have cooled a mechanical object to a temperature lower than previously thought possible, below the so-called “quantum limit.”

NIST researchers applied a special form of microwave light to cool a microscopic aluminum drum to an energy level below the generally accepted limit, to just one fifth of a single quantum of energy. Having a diameter of 20 micrometers and a thickness of 100 nanometers, the drum beat 10 million times per second while its range of motion fell to nearly zero. Image credit: Teufel/NIST

The new NIST theory and experiments, described in the Jan. 12, 2017, issue of Nature, showed that a microscopic mechanical drum—a vibrating aluminum membrane—could be cooled to less than one-fifth of a single quantum, or packet of energy, lower than ordinarily predicted by quantum physics. The new technique theoretically could be used to cool objects to absolute zero, the temperature at which matter is devoid of nearly all energy and motion, NIST scientists said.

“The colder you can get the drum, the better it is for any application,” said NIST physicist John Teufel, who led the experiment. “Sensors would become more sensitive. You can store information longer. If you were using it in a quantum computer, then you would compute without distortion, and you would actually get the answer you want.”

“The results were a complete surprise to experts in the field,” Teufel’s group leader and co-author José Aumentado said. “It’s a very elegant experiment that will certainly have a lot of impact.”

The drum, 20 micrometers in diameter and 100 nanometers thick, is embedded in a superconducting circuit designed so that the drum motion influences the microwaves bouncing inside a hollow enclosure known as an electromagnetic cavity. Microwaves are a form of electromagnetic radiation, so they are in effect a form of invisible light, with a longer wavelength and lower frequency than visible light.

The microwave light inside the cavity changes its frequency as needed to match the frequency at which the cavity naturally resonates, or vibrates. This is the cavity’s natural “tone,” analogous to the musical pitch that a water-filled glass will sound when its rim is rubbed with a finger or its side is struck with a spoon.

NIST scientists previously cooled the quantum drum to its lowest-energy “ground state,” or one-third of one quantum. They used a technique called sideband cooling, which involves applying a microwave tone to the circuit at a frequency below the cavity’s resonance. This tone drives electrical charge in the circuit to make the drum beat. The drumbeats generate light particles, or photons, which naturally match the higher resonance frequency of the cavity. These photons leak out of the cavity as it fills up. Each departing photon takes with it one mechanical unit of energy—one phonon—from the drum’s motion. This is the same idea as laser cooling of individual atoms, first demonstrated at NIST in 1978 and now widely used in applications such atomic clocks.

The latest NIST experiment adds a novel twist—the use of “squeezed light” to drive the drum circuit. Squeezing is a quantum mechanical concept in which noise, or unwanted fluctuations, is moved from a useful property of the light to another aspect that doesn’t affect the experiment. These quantum fluctuations limit the lowest temperatures that can be reached with conventional cooling techniques. The NIST team used a special circuit to generate microwave photons that were purified or stripped of intensity fluctuations, which reduced inadvertent heating of the drum.

“Noise gives random kicks or heating to the thing you’re trying to cool,” Teufel said. “We are squeezing the light at a ‘magic’ level—in a very specific direction and amount—to make perfectly correlated photons with more stable intensity. These photons are both fragile and powerful.”

The NIST theory and experiments indicate that squeezed light removes the generally accepted cooling limit, Teufel said. This includes objects that are large or operate at low frequencies, which are the most difficult to cool.

The drum might be used in applications such as hybrid quantum computers combining both quantum and mechanical elements, Teufel said. A hot topic in physics research around the world, quantum computers could theoretically solve certain problems considered intractable today.

The research was supported in part by the Defense Advanced Research Projects Agency.

Source: NIST

Next-Generation Optics Offer the Widest Real-Time Views of Vast Regions of the Sun

A groundbreaking new optical device, developed at NJIT’s Big Bear Solar Observatory (BBSO) to correct images of the Sun distorted by multiple layers of atmospheric turbulence, is providing scientists with the most precisely detailed, real-time pictures to date of solar activity occurring across vast stretches of the star’s surface.

The observatory’s 1.6-meter New Solar Telescope can now produce simultaneous images, for example, of massive explosions such as solar flares and coronal mass ejections that are occurring at approximately the same time across large structures such as a 20,000-mile-wide sunspot in the Sun’s photosphere.

Recent images taken from Big Bear Solar Observatory of a massive section of the Sun’s surface, about 23,000 miles square, showcase the advances in real-time clarity over vast distances presented by a groundbreaking new optics system.

“To understand the fundamental dynamics of the Sun, such as the origin of solar storms, we need to collect data from as wide a field of view as possible,” says Philip Goode, distinguished research professor of physics at NJIT and the leader of an international team of researchers funded by the National Science Foundation (NSF) to develop this next-generation optical system.

“During large flares, for example, magnetic field changes appear to occur at many different places with near simultaneity,” he explains. “Only by seeing the comprehensive array of eruptions all at once will we be able to accurately measure the size, strength and sequencing of these magnetic events and also analyze the forces that propel the star’s magnetic fields to twist around each other until they explode, spewing massive amounts of radiation and particles that, when directed earthward, can cause disruptive space weather.”

The multi-conjugate adaptive optics (MCAO) device sits downstream of the aperture of the BBSO telescope, currently the world’s highest-resolution solar telescope. The system is composed of three mirrors that change shape to correct the path of the incoming light waves, guided by a computer attached to ultra-fast cameras that take more than 2,000 frames per second to measure aberrations in the wave path. The system is called multi-conjugate because each of the three mirrors captures light from a different altitude – near the ground and at about three and six miles high – and the three corrected images together produce a distortion-free picture that eliminates the effects of turbulence up to about seven miles.

The MCAO system has tripled the size of the corrected field of view now available with the current technology, known as adaptive optics, which employs a single shape-shifting, or deformable, mirror to correct images. An article showcasing these advances was published today in the journal Astronomy Astrophysics.

“The gain of using three deformable mirrors instead of one is easily visible. The images are crisp in a much larger area,” says Dirk Schmidt, a post-doctoral researcher at the National Solar Observatory (NSO), a project scientist for the international MCAO team, and first author of the article describing the research.  “After many years of development, this is an important milestone for the new, wide-field generation of solar adaptive optics.”

Turbulent airflows at different layers of the Earth’s atmosphere, from the ground up to the jet stream, change the path of the Sun’s light faster than the human eye can compensate, blurring the images captured by conventional telescopes just as hot exhaust creates a haze on the roadway. The blurring occurs when air masses at different temperatures mix, distorting the propagation of the light and causing it to take an ever-changing, random path from the distant object, arriving at the observer with a randomized angle of incidence. That same atmospheric turbulence causes the twinkling of stars.

The MCAO team, which includes researchers from NJIT, NSO and the Kiepenheuer Institute for Solar Physics in Germany, has been working together for more than a decade on the next generation of adaptive optics to correct these distortions. The researchers succeeded in significantly widening the field of view after several years of alternating laboratory experimentation – with an artificial light source functioning as the Sun that emitted light waves purposefully distorted by the heat emanating from hot plates – with “on-sky” tests performed in real time in the BBSO’s optical path.

“Over the years, we had reconfigured the mirrors scores of times, waiting for that ‘Wow!’ moment,” Goode recalls.  “Finally, late last July, we saw what we had long sought – a continuous stream of sharp, wide-field corrected, but essentially identical images. There was stunned silence, followed by applause. We then repeated the test several times by looking at various places on the Sun to prove we had succeeded.  The final trick was narrowing the field to get a deeper-focused correction with each mirror, much like you would adjust a camera to have the near and far field in focus.”

The scientific gains are expected to be multi-level.  A clearer, more comprehensive view of solar activity should provide additional clues to researchers seeking to explain mysterious dynamics, such as the means by which explosions on the Sun produce magnetic explosions and radiation and accelerate particles to nearly the speed of light within seconds. The more scientists understand physical processes taking place more than 90 million miles away, the better policymakers will be able to predict and prepare for solar storms with the ferocity to disrupt communications satellites, knock out GPS systems, shut down air travel and quench lights, computers and telephones in millions of homes and businesses, notes Andrew Gerrard, director of NJIT’s Center for Solar-Terrestrial Research, which operates the BBSO and several other solar instruments around the world and in space.

“Correcting for multiple layers of turbulence in the atmosphere is an engineering tour-de-force,” comments Peter Kurczynski, director of the astronomical sciences program at the NSF that funded the research. “This study demonstrates technology that is crucial for next-generation observatories and it will improve our understanding of the sun. This is why NSF supports adaptive optics research, because new technologies enable scientific discoveries.”

The MCAO project also serves as a critical test of optical instruments that will be required by future solar telescopes.

“The MCAO results from BBSO constitute a real break though,” notes Thomas Rimmele, who is the project director for the coming 4-meter Daniel K. Inouye Solar Telescope (DKIST) in Hawaii, an associate director of the NSO and a co-investigator on the MCAO team.  He adds, “The system provides an essential experimental platform for the development of wide-field adaptive optics for solar observations, and serves as the pathfinder for adaptive optics systems on the DKIST, scheduled for regular operation in 2020.”

Source: NSF, New Jersey Institute of Technology

Controlling the properties of matter in two-dimensional crystals

By creating atomic chains in a two-dimensional crystal, researchers at Penn State believe they have found a way to control the direction of materials properties in two- and three-dimensional crystals with implications in sensing, optoelectronics and next-generation electronics applications.

Whether an alloy has a random arrangement of atoms or an arrangement that is ordered can have large effects on a material’s properties. In a paper published in Nano Letters, Nasim Alem, assistant professor of materials science and engineering, and colleagues at Penn State used a combination of simulations and scanning transmission electron microscopy (STEM) imaging to determine the atomic structure of an ordered alloy of molybdenum, tungsten and sulfur. They determined that fluctuations in the amount of available sulfur were responsible for the creation of atomic chains of either molybdenum or tungsten.

An electron microscopy image of ordered atoms of tungsten (W) and molybdenum (Mo) against artistic representations of triangular single layer flakes of WxMo1–xS2 on a substrate. Image Credit: Amin Azizi and Andrea Kohler/ Penn State

An electron microscopy image of ordered atoms of tungsten (W) and molybdenum (Mo) against artistic representations of triangular single layer flakes of WxMo1–xS2 on a substrate. Image credit: Amin Azizi and Andrea Kohler/ Penn State

“We discovered how chains form in a two-dimensional alloy as a result of fluctuations in the amount of a particular precursor, in this case sulfur,” said Alem. “Normally, when we combine atoms of different elements, we don’t know how to control where the atoms will go. But we have found a mechanism to give order to the atoms, which in turn introduces control of the properties, not only heat transport, as is the case in this work, but also electronic, chemical or magnetic properties in other alloy cases. If you know the mechanism, you can apply it to arrange the atoms in a wide range of alloys in 2D crystals across the periodic table.”

In the case of the molybdenum, tungsten and sulfur alloy, the researchers showed that the electronic properties were the same in every direction, but using simulations, they predict that the thermal transport properties are smaller perpendicular to the chains or stripes.

“We didn’t know why this crystal forms an ordered structure, so we worked with my colleague Dr. Vin Crespi to understand the underlying physics that causes order in this crystal,” said Alem. “Our calculations show it was the fluctuations in the third element, sulfur, that was determining how the chains formed.”

Vincent H. Crespi, distinguished professor of physics, and professor of chemistry and materials science and engineering, who developed the theoretical understanding of the phenomenon, said, “Although the interior of the flake is indifferent to whether molybdenum or tungsten occupies any site in the crystal lattice, the edge of the growing crystal does care: Depending on how much sulfur is available at a given location, the edge will prefer to be either 100 percent molybdenum or 100 percent tungsten. So as the availability of sulfur randomly varies during growth, the system alternately lays down rows of molybdenum or tungsten. We think this may be a general mechanism to create stripe-like structures in 2D materials.”

Amin Aziz, a Ph.D. candidate in Alem’s group and lead author, produced the STEM imaging and spectroscopy that showed the fine atomic structure of the alloy samples and their electronic properties.

“When we are able to directly image constitutive atoms of a substance, see how they interact with each other at the atomic level and try to understand the origins of such behaviors, we could potentially create new materials with unusual properties that have never existed,” said Azizi,

A team led by Mauricio Terrones, professor of physics, produced samples of this ordered alloy by vaporizing powders of all three elements, called precursors, under high heat.

Source: Penn State University

Physicists Leapfrog Accelerators with Ultrahigh Energy Cosmic Rays

An international team of physicists has developed a pioneering approach to using Ultrahigh Energy Cosmic Rays (UHECRs)—the highest energy particles in nature since the Big Bang—to study particle interactions far beyond the reach of human-made accelerators. The work, outlined in the journal Physical Review Letters, makes use of UHECR measurements by the Pierre Auger Observatory in Argentina, which has been recording UHECR data for about a decade.

An international team of physicists has developed a pioneering approach to using Ultrahigh Energy Cosmic Rays (UHECRs)—the highest energy particles in nature since the Big Bang—to study particle interactions far beyond the reach of human-made accelerators. The work makes use of UHECR measurements by the Pierre Auger Observatory in Argentina, which has been recording UHECR data for about a decade. Pictured above is one of the 1,660 stations of the surface detector of the Observatory. Image courtesy of the Pierre Auger Collaboration.

An international team of physicists has developed a pioneering approach to using Ultrahigh Energy Cosmic Rays (UHECRs)—the highest energy particles in nature since the Big Bang—to study particle interactions far beyond the reach of human-made accelerators. The work makes use of UHECR measurements by the Pierre Auger Observatory in Argentina, which has been recording UHECR data for about a decade. Pictured above is one of the 1,660 stations of the surface detector of the Observatory. Image courtesy of the Pierre Auger Collaboration.

The study may also point to the emergence of some new, not-yet-understood physical phenomenon at an order-of-magnitude higher energy than can be accessed with the Large Hadron Collider (LHC), where the Higgs particle was discovered.

The origin of UHECRs remains a mystery, in spite of decades of work aimed at discovering their sources. Yet even before the UHECRs’ sources are identified, the particle showers they create in the Earth’s atmosphere can be used for exploring fundamental physics.

The cosmic rays are atomic nuclei. When they collide with air particles, hundreds of additional particles are created, which then further interact to produce a cascade of particles in the atmosphere. The Observatory’s telescopes measure how the shower develops as it travels through the atmosphere, and its surface detectors gauge the particle content of the shower on the ground. The difficulty of using UHECR air showers to study particle physics, up to now, stemmed from the uncertainty in an individual ray’s energy and not knowing exactly what nucleus it is.

New York University Physics Professor Glennys Farrar and Jeff Allen, her graduate student and postdoctoral researcher at the time of the study, circumvented this by using the atmosphere similar to the way a particle detector is employed in laboratory experiments. For the Physical Review Letters study, they compared the Observatory data for 441 UHECR showers, with computer-simulated showers based on particle physics models derived from experiments at accelerator energies.

“State-of-the-art particle physics models seriously underestimate a key component of these UHECR showers,” explains Farrar. “This may point to the emergence of unanticipated physical processes at higher energy than the LHC. Future studies, and planned upgrades to the PAO, should reveal what produces the extra signal, providing a window on particle physics far beyond the reach of accelerators.”

Source: NSF, New York University