Every proton contains three quarks: two up and one down. But charm quarks, heavier than the proton itself, have been found inside. How?
A temperature not seen since the first microsecond of the birth of the universe has been recreated by scientists, and they discovered that the event did not unfold quite the way they expected. The interaction of energy, matter, and the strong nuclear force in the ultra-hot experiments conducted at the Relativistic Heavy Ion Collider (RHIC) was thought to be well understood. However, a detailed investigation has revealed that physicists are missing something in their model of how the universe works. A recent paper detailing the findings appears in the journal Physical Review Letters.
“It’s the things you weren’t expecting that are really trying to tell you something in science,” says Steven Manly, associate professor of physics and astronomy at the University of Rochester and co-author of the paper. “The basic nature of the interactions within the hot, dense medium, or at least the manifestation of it, changes depending on the angle at which it’s viewed. We don’t know why. We’ve been handed some new pieces to the puzzle and we’re just trying to figure out how this new picture fits together.”
“They said, ‘This can’t be. You’re violating boost invariance.’ But we’ve gone over our results for more than a year, and it checks out.” —
A team of researchers from France has developed the first three-directional hybrid quantum inertial sensor, which can measure acceleration without using satellite signals. At the heart of this breakthrough device is something called “matter wave interferometry,” which uses two distinct characteristics of quantum mechanics: wave-particle duality and superposition.
In the cloud
The device consists of a cloud of rubidium atoms that are cooled to temperatures nearing absolute zero. The atoms are placed in a vacuum and are in free fall due to gravity.
Scientists are trying to work out if a strange new particle, dubbed a “ghost particle”, has been detected at CERN’s Large Hadron Collider (LHC) in Switzerland.
Using the Compact Muon Solenoid (CMS) instrument on the particle accelerator, the team said they had seen a signal that could be a particle that’s twice the mass of a carbon atom. But as the particle does not fit known theories, it could cause a bit of a stir if it exists. Their findings, which have not yet been peer-reviewed, are available on arXiv.
“I’d say theorists are excited and experimentalists are very skeptical,” Alexandre Nikitenko, a theorist on the CMS team who worked on the data, told The Guardian. “As a physicist I must be very critical, but as the author of this analysis I must have some optimism too.”
Using a chain of atoms in single-file to simulate the event horizon of a black hole, a team of physicists has observed the equivalent of what we call Hawking radiation – particles born from disturbances in the quantum fluctuations caused by the black hole’s break in spacetime.
This, they say, could help resolve the tension between two currently irreconcilable frameworks for describing the Universe: the general theory of relativity, which describes the behavior of gravity as a continuous field known as spacetime; and quantum mechanics, which describes the behavior of discrete particles using the mathematics of probability.
For a unified theory of quantum gravity that can be applied universally, these two immiscible theories need to find a way to somehow get along.
The most common particles are electrons and photons, which are understood to be examples from the great families of fermions and bosons, to which all other particles in nature belong. But there is another possible category of particles, the so-called anyons. Anyons are predicted to arise inside materials small enough to confine the electronic state wave function, as they emerge from the collective dance of many interacting electrons.
One of these is named Majorana zero mode, anyonic cousins to the Majorana fermions proposed by Ettore Majorana in 1937. Majoranas, as these hypothetical anyons are affectionally called, are predicted to exhibit numerous exotic properties, such as simultaneously behaving like a particle and antiparticle, allowing mutual annihilation, and the capability to hide quantum information by encoding it nonlocally in space. The latter property specifically holds the promise of resilient quantum computing.
Since 2010, many research groups have raced to find Majoranas. Unlike fundamental particles, such as the electron or the photon, which naturally exist in a vacuum, Majorana anyons need to be created inside hybrid materials. One of the most promising platforms for realizing them is based on hybrid superconductor-semiconductor nanodevices. Over the past decade, these devices have been studied with excruciating detail, with the hope of unambiguously proving the existence of Majoranas. However, Majoranas are tricky entities, easily overlooked or mistaken with other quantum states.
Researchers from the University of Tsukuba have shown how adding a tiny resonator structure to an ultrafast electron pulse detector reduced the intensity of terahertz radiation required to characterize the pulse duration (ACS Photonics, “Streaking of a Picosecond Electron Pulse with a Weak Terahertz Pulse”).
To study proteins—for example, when determining the mechanisms of their biological actions—researchers need to understand the motion of individual atoms within a sample. This is difficult not just because atoms are so tiny, but also because such rearrangements usually occur in picoseconds—that is, trillionths of a second.
One method to examine these systems is to excite them with an ultrafast blast of laser light, and then immediately probe them with a very short electron pulse. Based on the way the electrons scatter off the sample as a function of the delay time between the laser and electron pulses, researchers can obtain a great deal of information about the atomic dynamics. However, characterizing the initial electron pulse is difficult and requires complex setups or high-powered THz radiation.
The cosmic optical background (COB) is the visible light emitted by all sources outside of the Milky Way. This faint glow of light, which can only be observed using very precise and sophisticated telescopes, could help astrophysics to learn more about the origins of the universe and what lies beyond our galaxy.
Last year, physicists working at different institutes across the United States published the most precise COB measurements collected so far, gathered by the New Horizons spacecraft, an interplanetary space probe launched by NASA over a decade ago. These measurements suggested that the COB is two times brighter than theoretical predictions.
Researchers at Johns Hopkins University have recently carried out a theoretical study exploring the possibility that this observed excess light could be caused by the decay of a hypothesized type of dark matter particles, known as axions. In their paper, published in Physical Review Letters, they showed that axions with masses between 8 and 20 eV could potentially account for the excess COB flux measured by the New Horizons team.
A new computational analysis by theorists at the U.S. Department of Energy’s Brookhaven National Laboratory and Wayne State University supports the idea that photons (a.k.a. particles of light) colliding with heavy ions can create a fluid of “strongly interacting” particles. In a paper just published in Physical Review Letters, they show that calculations describing such a system match up with data collected by the ATLAS detector at Europe’s Large Hadron Collider (LHC).
As the paper explains, the calculations are based on the hydrodynamic particle flow seen in head-on collisions of various types of ions at both the LHC and the Relativistic Heavy Ion Collider (RHIC), a DOE Office of Science user facility for nuclear physics research at Brookhaven Lab. With only modest changes, these calculations also describe flow patterns seen in near-miss collisions, where photons that form a cloud around the speeding ions collide with the ions in the opposite beam.
“The upshot is that using the same framework we use to describe lead-lead and proton-lead collisions, we can describe the data of these ultra-peripheral collisions where we have a photon colliding with a lead nucleus,” said Brookhaven Lab theorist Bjoern Schenke, a co-author of the paper. “That tells you there’s a possibility that in these photon-ion collisions, we create a small dense strongly interacting medium that is well described by hydrodynamics—just like in the larger systems.”
Measurements of solar neutrinos proved that our star is powered by nuclear reactions and has brought to light many other details about the Sun’s inner workings. They also led to the discovery of neutrino oscillations—a phenomenon that is difficult to reconcile with established theories. Current neutrino research mostly relies on neutrinos generated on Earth by reactors and accelerators. But some physicists argue that there is still a lot to be done with neutrinos generated in the Sun. A new generation of solar-neutrino experiments may help in solving outstanding questions about both neutrinos and solar physics, these scientists say.
The study of solar neutrinos began in the late 1960s. Using a detector filled with dry-cleaning fluid and placed in South Dakota’s Homestake gold mine, physicist Raymond Davis and his colleagues observed the first neutrino signal from the Sun. They were surprised, however, to find that the number of neutrinos was one third of what models predicted—a mystery that led to a “neutrino gold rush,” with many new experiments staking claims to different energy and length scales related to the neutrino behavior. Eventually, physicists explained the missing neutrinos as resulting from oscillations between neutrino flavors (see Nobel Focus: Neutrino and X-ray Vision). These oscillations implied that neutrinos have mass, in tension with the standard model of particle physics.
The study of neutrino oscillations continues with efforts to pin down the neutrino masses and mixing parameters that determine the oscillating behavior. The main target, however, is no longer solar neutrinos. “The majority of the community, by a large margin, is focused on accelerator neutrinos,” says Michael Smy from the University of California, Irvine. The reason for this shift, he says, is that an accelerator experiment can explore higher-energy neutrinos and control the source-detector distance over which oscillations may occur. Researchers can also switch the accelerator on and off, which helps remove certain backgrounds.
