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Category: particle physics

CERN’s colossal complex of accelerators is in the midst of a two-year shutdown for upgrade work. But that doesn’t mean all experiments at the Laboratory have ceased to operate. The CLOUD experiment, for example, has just started a data run that will last until the end of November.

The CLOUD experiment studies how ions produced by high-energy particles called cosmic rays affect aerosol particles, clouds and the climate. It uses a special cloud chamber and a beam of particles from the Proton Synchrotron to provide an artificial source of cosmic rays. For this run, however, the cosmic rays are instead natural high-energy particles from cosmic objects such as exploding stars.

“Cosmic rays, whether natural or artificial, leave a trail of ions in the chamber,” explains CLOUD spokesperson Jasper Kirkby, “but the Proton Synchrotron provides cosmic rays that can be adjusted over the full range of ionisation rates occurring in the troposphere, which comprises the lowest ten kilometres of the atmosphere. That said, we can also make progress with the steady flux of natural cosmic rays that make it into our chamber, and this is what we’re doing now.”

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Circa 2010

Ultra-fast pulses from a powerful laser can create droplets of water out of thin air, according to a new study. With the right conditions and large enough droplets, the researchers say, the technique could be used to make rain on demand.

Rain forms when water condenses around tiny particles in the atmosphere. Most of the time, dust or pollen do the job, but humans have long attempted to speed the process by seeding clouds with chemicals like silver iodide. Those chemicals provide the so-called “condensation nuclei” that trigger the consolidation of water into raindrops.

Unfortunately, such methods are difficult and could have environmental side effects, said Jérôme Kasparian, an optical physicist at the University of Geneva, Switzerland who was on the team that demonstrated the laser-triggered condensation. The study was published online May 2 in the journal Nature Photonics.

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Scientists have observed a quantum vibration at normal room temperature for the first time, a phenomenon that usually requires ultra-cold, carefully calibrated conditions – bringing us another step closer to understanding the behaviour of quantum mechanics in common materials.

The team was able to spot a phonon, a quantum particle of vibration generated from high-frequency laser pulses, in a piece of diamond. These phonons are notoriously hard to detect, partly because of their sensitivity to heat.

What makes observing a phonon so important is that it shows a vibration acting as a single unit of energy (as described by quantum mechanics), as well as a wave (as described by classical physics). At room temperature in open air conditions, it brings quantum behaviour “closer to our daily life” in the words of the researchers.

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Dive into the subatomic world, into the heart of protons or neutrons, and you’ll find elementary particles known as quarks. Measuring the mass of these quarks can be challenging, but new results from the CMS collaboration reveal for the first time how the mass of the top quark – the heaviest of six types of quarks – varies depending on the energy scale used to measure the particle.

The theory of quantum chromodynamics, a component of the Standard Model, predicts this energy-scale variation, known as running, for the masses of all quarks and for the strong force acting between them. Observing the running masses of quarks can therefore provide a way of testing quantum chromodynamics and the Standard Model.

Experiments at CERN and other laboratories have already measured the running masses of the bottom and charm quarks, the second and third heaviest quarks, and the results were in agreement with quantum chromodynamics. Now, the CMS collaboration has used data from high-energy proton–proton collisions at the Large Hadron Collider to chase out the running mass of the top quark.

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Dark matter, which researchers believe make up about 80% of the universe’s mass, is one of the most elusive mysteries in modern physics. What exactly it is and how it came to be is a mystery, but a new Johns Hopkins University study now suggests that dark matter may have existed before the Big Bang.

The study, published August 7 in Physical Review Letters, presents a new idea of how was born and how to identify it with astronomical observations.

“The study revealed a new connection between particle physics and astronomy. If dark matter consists of new particles that were born before the Big Bang, they affect the way galaxies are distributed in the sky in a unique way. This connection may be used to reveal their identity and make conclusions about the times before the Big Bang too,” says Tommi Tenkanen, a postdoctoral fellow in Physics and Astronomy at the Johns Hopkins University and the study’s author.

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One of the fundamental challenges of physics is the reconciliation of Einstein’s theory of relativity and quantum mechanics. The necessity to critically question these two pillars of modern physics arises, for example, from extremely high-energy events in the cosmos, which so far can only ever be explained by one theory at a time, but not both theories in harmony. Researchers around the world are therefore searching for deviations from the laws of quantum mechanics and relativity that could open up insights into a new field of physics.

For a recent publication, scientists from Leibniz University Hannover and Ulm University have taken on the twin paradox known from Einstein’s special theory of relativity. This thought experiment revolves around a pair of twins: While one brother travels into space, the other remains on Earth. Consequently, for a certain period of time, the twins are moving in different orbits in space. The result when the pair meets again is quite astounding: The twin who has been travelling through space has aged much less than his brother who stayed at home. This phenomenon is explained by Einstein’s description of time dilation: Depending on the speed and where in the gravitational field two clocks move relative to each other, they tick at different speeds.

For the publication in Science Advances, the authors assumed a quantum-mechanical variant of the twin paradox with only one twin. Thanks to the superposition principle of , this twin can move along two paths at the same time. In the researchers’ , the twin is represented by an . “Such clocks use the quantum properties of atoms to measure time with high precision. The atomic clock itself is therefore a quantum-mechanical object and can move through space-time on two paths simultaneously due to the superposition principle. Together with colleagues from Hannover, we have investigated how this situation can be realised in an experiment,” explains Dr. Enno Giese, research assistant at the Institute of Quantum Physics in Ulm. To this end, the researchers have developed an experimental setup for this scenario on the basis of a quantum-physical model.

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The standard model of physics remains incomplete. Could supersymmetry fill the gaps? From whether supersymmetric particles could fix the mass of the Higgs Boson to what this would mean for string theory, the world’s leading thinkers explain all.

John Ellis is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King’s College London. He was Division Leader for the CERN theory division, a founding member of the LEPC and of the LHCC at CERN and currently chair of the committee to investigate physics opportunities for future proton accelerators.

Catherine Heymans is a Professor of Astrophysics and European Research Council Fellow at the University of Edinburgh. She is also the Director of the German Centre for Cosmological Lensing at the Ruhr-University Bochum, Germany.

Ben Allanach is a member of the Department of Applied Mathematics and Theoretical Physics High Energy Physics research group and The Cambridge SUSY Working Group based at the Cavendish Laboratory.

Subir Sarkar is a physicist at the University of Oxford, where he is head of the Particle Theory Group at the Rudolf Peierls Centre for Theoretical Physics. His research interests are at the interface between fundamental physics and astrophysics & cosmology — specifically theoretical aspects of dark matter, inflation and large-scale structure formation.

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When a single neutrino was detected by a neutrino detector in Antarctica in September 2017, it was the start of something amazing. It was to become the first-ever high-energy neutrino that astronomers could trace back to an origin — a blazar galaxy called TXS 0506+056, 3.8 billion light-years away.

But, in the manner of many great discoveries, that revelation opened up a whole new can of questions, including this: why, of all the galaxies with similar properties, has a neutrino only ever been traced to this one?

Now, astronomers have found a possible answer, pinpointing the source event that produced this neutrino. The relativistic jet blasting out of a supermassive black hole could have acted as a cosmic particle collider, producing a flurry of neutrinos that, due to the shape and wobble of the jet, ended up streaming through Earth.

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As quantum objects are susceptible to their surrounding environment, quantum coherence and quantum states can easily be destroyed due to the impact of external signals, which can include thermal noise and backscattered signals in the measurement circuit. Researchers have thus been trying to develop techniques to enable nonreciprocal signal propagation, which could help to block the undesired effects of backward noise.

In a recent study, members of the dynamic spintronics group at the University of Manitoba in Canada have proposed a new method to produce dissipative coupling in hybrid quantum systems. Their technique, presented in a paper published in Physical Review Letters, enables nonreciprocal signal propagation with a substantial isolation ratio and flexible controllability.

“Our recent work on nonreciprocity in cavity magnonics is grounded in a research area combining cavity spintronics and hybrid quantum systems, which holds promise for constructing new quantum information processing platforms,” Yi-Pu Wang, a postdoctoral researcher at the University of Manitoba who was involved in the study, told Phys.org.

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