Meet the glueball, the missing Standard Model particle

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Glueballs are the missing frontier of the Standard Model

There should be particles made entirely of gluons, but we don’t know how to find them

For Ars Technica:

The discovery of the Higgs boson was rightfully heralded as a triumph of particle physics, one that brought completion to the Standard Model, the collection of theories that describes particles and their interactions. Lost in the excitement, however, was the fact that we’re still missing a piece from the Standard Model—another type of particle that doesn’t resemble any other we’ve yet seen.

The particle is a glueball, but its goofy name doesn’t express how interesting it is. Glueballs are unique in that they don’t contain any matter at all: they have no quarks or electrons or neutrinos. Instead, they are made entirely of gluons, which are the particles that bind quarks together inside protons, neutrons, and related objects.

Particle physicists are sure they exist, but everything else about them is complicated, to say the least. Like so many other exotic particles (including the Higgs), glueballs are very unstable, decaying quickly into other, less massive particles. We don’t have any ideas about their masses, however, which is obviously kind of important to know if you want to find them. We also don’t know exactly how they decay, making it hard to know exactly how we’ll identify them in experiments. [Read the rest at Ars Technica….]

Traces of particles from the first second after the Big Bang

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Signs of neutrinos from the dawn of time, less than a second after the Big Bang

First unambiguous observation of the cosmic neutrino background

From Ars Technica:

The first 400,000 years after the Big Bang are inaccessible to us by using light; the material that filled the entire cosmos made it opaque. However, neutrinos interact very little with ordinary matter, so they could travel right through the opaque mess. Lots of these low-mass, fast-moving particles were formed in the first second after the Big Bang, so they could provide a sensitive probe of some of the very earliest moments in the Universe.

Unfortunately, these primordial neutrinos have never been detected directly, and they may have too little energy for us to ever detect them. But a new paper published in Physical Review Letters showed an unambiguous indirect detection using measurements of the cosmic microwave background light. This article marks the first clear measurement of the cosmic neutrino background, which is a significant confirmation of one of the major predictions of the Big Bang model. [Read the rest at Ars Technica…]

No quantum foam seen in the cosmic beer glass

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Light from distant black holes doesn’t surf on waves of quantum foam

Strongest check yet on quantum gravity effects in astronomy turns up nothing

For Ars Technica:

Quantum gravity is notoriously slippery. While the Standard Model successfully describes three forces of nature, it doesn’t include gravity, so gravity still has no consistent quantum theory. To make matters worse, gravity is so weak that it’s difficult to probe at the sorts of energies where any minuscule quantum effects would pop out. However, some researchers predict that those tiny effects could accumulate over cosmological distances: light traveling from far-off quasars would be changed by the “quantum foam” of spacetime, producing blurry images in our telescopes—or even making objects seem to disappear.

A new report by E. S. Perlman and colleagues examines the disappearance hypothesis using gamma-ray data from quasars. In particular, they investigated a possibility suggested by the holographic principle, the idea that all the information in the cosmos can be encoded on the two-dimensional boundary that encloses it. Disappointingly for fans of quantum foam, the gamma ray data did not show any measurable fading or blurring of the quasars.

As the authors point out, these results don’t rule out anything general regarding quantum gravity, quantum foam, or the holographic principle. But they do provide the tightest constraint yet on cumulative effects of quantum foam on light traveling across the Universe. [Read the rest at Ars Technica…]

A white dwarf murder mystery

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What killed the white dwarfs? (Aside from the giant explosion)

Merger or extra matter? Two papers come to opposite conclusions

For Ars Technica:

Type Ia supernovae are explosions that occur when white dwarfs strip matter off a companion star, exceed their maximum possible mass, and blow up.

No, wait: type Ia supernovae are the explosions caused when two white dwarfs collide.

While it’s reasonably certain that white dwarfs—the Earth-size remnant of stars similar to the Sun—are involved, the observational evidence for how these supernovae actually explode is messy. This week’s issue of Nature is a prime example: two back-to-back papers provide evidence for a white dwarf-companion star explosion and a two-white-dwarf collision scenario, respectively. Ultimately, these apparently contradictory results could mean there are two distinct types of white dwarf supernovae… or that we still don’t understand what’s going on.

The stakes are high. Unlike other supernovae, which involve the death of a star much more massive than the Sun, type Ia supernovae all explode in very similar ways. The pattern of light they emit during and after the explosion provides a reliable measurement of how far away they are. Since supernovae are bright enough to be visible from billions of light-years away, astronomers use them to measure the expansion and acceleration rate of the Universe, as recognized in the 2011 Nobel Prize in physics. Because they are so important to cosmology, researchers want to understand what objects are involved in the explosion and exactly how they blow up. [Read the rest at Ars Technica…]

Bathing asteroids with nuclear weapons

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A gentle nudge with a nuke: deflecting Earth-bound asteroids

From Ars Technica:

In 2013, a small asteroid exploded in the atmosphere over Chelyabinsk, Russia. The sonic boom from the event sent more than a thousand people to the hospital, mostly from flying glass from shattered windows. The Chelyabinsk meteor was a relatively small chunk of space rock—asteroid researchers think it was probably about 20 meters (66 feet) across—but exploding over a city made it a noteworthy event. It’s probable many similar asteroids hit Earth on a regular basis, but most don’t happen to fly over metropolitan areas; they fall into the ocean or over lightly populated regions.

However, Earth has played target in the cosmic darts tournament before. Meteor Crater in Arizona, the Tunguska impact in Siberia in 1908, and most famously the Chicxulub asteroid in Mexico (which played a part in the extinction of the dinosaurs) are just three of many known examples. That’s why many people are looking at viable options for planetary defense: destroying or turning asteroids aside before they can hit Earth. And planetary defense is one reason the United States’ National Nuclear Safety Administration (NNSA) has given for not destroying some of its surplus nuclear warheads. [Read the rest at Ars Technica…]

Captain Picard may be a little confused.

Today, researchers with the LHCb experiment at CERN announced the confirmation of a weird object that first appeared in detectors in 2008. This object is made up of four quarks, where other particles are made of two or three quarks (or zero, in the case of electrons, neutrinos, and the like). But what sort of beast is this? As is often the case, more work is needed before we can say for ccertain.

With that much data, physicists were able to determine the composition of the Z(4430): it consists of a charm quark, a charm anti-quark, a down quark, and an up antiquark. The “4430” part of the name indicates its mass: 4,430 million electron-volts, which a little more than four times the mass of a proton (938 million electron volts). The combination of quarks gives the Z(4430) a negative electric charge, hence the “-” in the label. The particle is highly unstable, so none of them are expected to be seen in nature. [Read more…]

Four quarks for Muster Mark!

The particles of the the Standard Model and its simplest supersymmetric version. [Credit:  Pauline Gagnon]

The particles of the the Standard Model and its simplest supersymmetric version. [Credit:
Pauline Gagnon]

Symmetry and elegance have proven to be a very successful way to think about the physical Universe. Arguably the greatest successes in 20th century particle physics came from translating mathematical symmetries into predictions about the results of particle collisions. However, not every symmetry thus far has led to a successful theory, and one of the frustrations is that a natural consequence of a symmetry in the theory of relativity hasn’t produced the predicted particles. The currently unfulfilled theory is known as supersymmetry (or SUSY), and so far none of its predictions have borne out experimentally.

However, a completely analogous version of SUSY could exist in certain exotic superconductors. This is not built out of elementary particles, but out of interactions between electrons and atoms, giving rise to a set of particle-like quantum excitations known as quasiparticles.

The new paper discussed the idea of emergent SUSY-like behavior in topological superconductors. In these systems (described in more detail in the sidebar story), the interior of the material conducts electricity without resistance, but the outside is an ordinary conductor. The authors argued that experimentally observed magnetic behavior on the conducting surface could be interpreted super symmetrically. It also exhibits a breaking of SUSY due to the fundamental difference in interior and surface behavior of the system.

In this view, the magnetic excitations (acting like bosons) on the surface are SUSY partners with the topological superconductor quasiparticles, which are fermions. [read more…]

Supersymmetry in…superconductors?