We have long had a seemingly simple question about neutrinos: how much do they weigh? Now, a gigantic experiment in China is poised to find out – and the answer could transform particle physics forever
Category: particle physics – Page 13
Individual atomic collisions can now be detected in the lab, potentially opening up pathways to new physics
Tiny atoms and molecules are constantly bombarding each other all around us. While we regularly measure the large-scale effects of these interactions, measuring the effect of each individual collision is far more difficult. But now, researchers have managed to measure how tiny gas particles affect a single silica particle in the lab. In their new study, published in Physical Review Letters, the team describes how they detected the momentum transfers of individual collisions of gas particles with a nanoparticle levitated in laser light.
On a large scale, the billions of constant collisions in the air create what we experience as pressure. At higher altitudes, the particles are more spread out and the pressure is weaker than at sea level. The same thing happens in liquids, resulting in increasing pressures at increasing depths. Researchers have all kinds of tools (and multiple units) for measuring pressure.
In 1827, Robert Brown noticed that grains of pollen jiggled in water under a microscope. Later work by Einstein showed that this random movement of particles suspended in a fluid was caused by constant collisions with fast-moving atoms or molecules in the surrounding medium, now referred to as “Brownian motion.” Usually, the individual impacts are too small and frequent to distinguish without getting lost in background noise.
Detecting the Kick of a Single Gas Molecule
An experiment resolves the tiny momentum transferred from an individual gas molecule to a levitated nanoparticle.
For two centuries, collisions between atoms or molecules and small suspended objects have been understood only statistically. In 1827, Robert Brown first described the random motion of pollen in water. Eight decades later, Albert Einstein and Marian Smoluchowski independently explained the jitter as the accumulated effect of countless unseen molecular impacts—convincingly demonstrating the physical reality of atoms and molecules. However, individual kicks were never resolved. Only their collective consequence, Brownian motion, was ever visible. Modern trapped-ion experiments succeeded in watching individual atom–ion collisions perturb a single confined ion’s motion [1]. But there, the “projectile” and the “sensor” were both individual atomic-scale particles of comparable mass. Now David Moore at Yale University and his colleagues have extended single-collision detection to a very different regime [2].
Forgotten particle could answer mystery of why we exist, say physicists
Scientists have unveiled a new theory on the birth of the cosmos, suggesting the early universe was shaped by an ancient particle that has been overlooked for decades.
Their research tackles one of the greatest conundrums in modern physics—how matter triumphed over antimatter in the aftermath of the Big Bang.
According to current theories, both should have annihilated each other after a colossal explosion, leaving nothing but an empty universe of pure energy. But physicists at the University of Southampton and the Indian Institute of Technology Kanpur say they found a clue in a neutrino, one of the lightest particles in the universe.
Scientists redetermine a key strontium frequency with 50 times better precision for quantum technologies
The Korea Research Institute of Standards and Science (KRISS) has remeasured a key transition frequency of the strontium (Sr) atom for the first time in 88 years, since 1938, using a photonic grating chip. It has established a new absolute frequency value with a measurement uncertainty reduced by more than 50 times. By providing an accurate reference value for next-generation quantum technologies, this achievement is expected to contribute to the precise control and miniaturization of quantum devices, including atomic clocks and neutral-atom quantum computers. The work is published in the journal Metrologia.
Strontium is an atom widely used in precision quantum technologies such as optical lattice clocks and quantum sensors. To use strontium in these technologies, fast-moving atoms must be slowed down and trapped with precisely tuned lasers. This requires knowing the exact resonant frequency of the laser light for the atomic transition.
However, the previous frequency value was obtained in 1938 by comparing the solar spectrum with the arc light of strontium, and its uncertainty was too large for today’s precise laser frequency settings. As a result, researchers have had to observe the atoms’ response directly and adjust the laser frequency as needed, much like turning the dial of an analog radio to tune in to a station.
New monolithic ion trap opens quantum simulations to more researchers
Some quantum systems are so complex that even the most powerful supercomputers struggle to simulate their behavior. One solution is quantum simulation: building a controllable quantum system in the lab and tuning it to mimic the one researchers want to understand.
In a trapped-ion simulator, a row of individual charged atoms, or ions, is held in place by electric fields inside a device called an ion trap. Lasers are used to make the ions interact in a manner that simulates the quantum system, and then researchers measure the information encoded in the ions to reveal the system’s properties.
Rice University’s Guido Pagano, along with collaborators at Duke University and Translume Inc., has developed a new kind of trapped-ion simulator, called a monolithic segmented 3D ion trap. This trap allowed the team to study these complex systems using heavy ions like ytterbium.
What Kills Schrödinger’s Cat? Scientists Just Ruled Out a 60-Year-Old Theory
Gravity has been proposed as a reason quantum superpositions become difficult to observe in everyday objects. A new experiment challenges one longstanding model of this process.
A detector buried deep beneath an Italian mountain has challenged a decades-old theory about why quantum behavior disappears from the world we experience. After 62 days of measurements, researchers found no trace of the faint radiation predicted by a model in which gravity disrupts quantum states. The result rules out this particular explanation while leaving open the possibility that gravity contributes to quantum decoherence.
Decoherence helps explain why particles can display unusual quantum behavior, such as existing in superpositions of different states, while everyday objects appear to follow classical physics. “One of the deepest questions in modern physics is why the strange quantum behavior that governs atoms and elementary particles seems to disappear in the macroscopic world we experience every day,” says Catalina Curceanu, director of research and spokesperson for the VIP Collaboration at the National Laboratory of Frascati of the National Institute for Nuclear Physics (INFN-LNF) in Italy.
Researchers Unleash Record-Breaking X-Ray Flashes in Just 300 Attoseconds
Researchers used the European XFEL to produce ultrashort X-ray flashes that reached record intensity for this type of pulse.
To understand chemical reactions and perhaps one day control the electrons involved, scientists need a detailed picture of how electrons behave inside atoms and molecules. X-rays offer a way to probe that behavior, but the flashes can also change the sample they are meant to examine. Researchers therefore need enough light to gather useful information before those changes become substantial.
At the European XFEL, a team has now concentrated X-ray flashes onto an area roughly 100,000 times smaller than the cross-section of a typical human hair. The pulses lasted an estimated 300 attoseconds, with each attosecond equal to a billionth of a billionth of a second.
Generative diffusion surrogates with analytical variance schedule
Image generators tune their noise by trial and error, because pictures have no clock. Turbulent plasmas do. By syncing an AI’s noise to the known rate at which particles spread, researchers built a surrogate that matches lab measurements—no tuning required.
The problem: Scientists often need fast, cheaper stand-ins (“surrogates”) for complex computer simulations of physical systems—in this case, systems where particles spread out over time, like heat diffusing or particles scattered by turbulence. A good stand-in should capture not just the average behavior but the full range of possible outcomes, including how spread out and lopsided the distribution becomes.
The tool they used: Generative diffusion models—the same kind of AI behind image generators—work by gradually adding noise to data and learning to reverse that process. But in image generation, there’s no physical meaning to “how much noise at each step”; the schedule is just a tuning choice. In particle transport, though, physicists already know how fast the spread (variance) grows over time, even without knowing the full distribution.
The key idea: The researchers set the noise schedule to match the known rate of spreading. This turns the model’s internal “time” into a real physical clock. The model then learns only the finer details—how the shape of the distribution evolves—without needing actual simulation data at intermediate times.
The result: Tested on particles moving through turbulent plasmas (going from fast, straight-line motion to slow diffusion), the surrogate reproduced the simulated particle distributions, matched the spread measured in the lab, and captured how the distribution’s shape (its “kurtosis,” or tailedness) evolved—all without any hand-tuning. This makes it useful both for fast emulation and for statistical inference from data.
#ArtificialIntelligence #PlasmaPhysics #turbulence #DiffusionModels
Solving the gallium anomaly: New calculation may explain neutrino shortfall without invoking new particles
Glimpses of the “gallium anomaly” were first seen in the mid-1990s, but it was first clearly discovered and stated in 2007 by neutrino physicist Carlo Giunti of Italy. The problem is simple to state but potentially very important: about 20% fewer electron neutrinos were seen to be captured by gallium nuclei than expected.
But now the anomaly looks to be explained with a new calculation by a collaboration of physicists at Italian universities and research laboratories—and the calculation agrees with the observed number of electron neutrinos captured. Their work is published in the journal Physical Review Letters.
When an electron neutrino (one of the three types of neutrinos) collides with a neutron in the nucleus of gallium-71 (⁷¹Ga), an electron is produced and the neutron transforms to a proton as a down quark converts to an up quark. The gallium nucleus then becomes a germanium-71 (⁷¹Ge) nucleus. This is a weak force interaction with a W+ particle exchange, a so-called charged-current weak interaction, and was historically important to the solar neutrino problem recognized in the 1960s.